Semester 1

Question 1

What contains 2 fatty acids, a glycerol and a phosphdiester bond?

Answer 1

Phosphatidyl Serine

Question 2

What is NOT a key feature of cholesterol?

Answer 2

It is responsible for determination of ABO blood groups

Question 3

What are the key features of cholesterol?

Answer 3

It is utilised to synthesise bile acids involved in digestion
It contains a steroid ring
It anchors proteins within plasma membrane (lipid raft)
It is a precursor for steroid hormones

Question 4

What explains why cholesterol controls the fluidity of the plasma membrane?

Answer 4

Separates hydrocarbon chains of phospholipids in the plasma membrane so that they cannot interact and become more rigid.
Rigid structure works like bookends

Question 5

Which part of cholesterol might enable it to be considered as amphipathic?

Answer 5

Hydroxyl group

This group has unequal sharing of electrons so generates a slight + / - end to covalent bond leading to interaction with H20 molecules = soluble in water

Question 6

What effect does increasing cholesterol concentration within cell membrane have on membrane fluidity?

Answer 6

Increase in fluidity!

Because it immobilises the first 1/3 of phospholipid molecule due to interaction between FA tails and steroid ring structure.

Question 7

What are components of a cell membrane?

Answer 7

Phosphatidyl ethanolamine
Glycolipids
Glycoproteins

Question 8

What is the role of the plasma membrane?

Answer 8

Create a semi permeable and dynamic barrier

Question 9

What explains the meaning of ‘Cholesterol is amphipathic’?

Answer 9

Polar head and rings interact with similar phospholipid regions

OH group interacts with phospholipid heads and the rest of the molecule with fatty acid tails

Question 10

HMG CoA reductase is the rate limiting enzyme in cholesterol synthesis.
What affects its action?

Answer 10

High cellular cholesterol levels due to uptake of LDL from blood.

Cellular levels of LDL ^ after uptake by endocytosis leads to ^ HMG CoA reductase degradation.

Question 11

What is correct about lipid rafts?

Answer 11

They keep protein subunits together

Can also keep them apart to avoid overactivation

Question 12

Under what circumstances might something need to cross the cell membrane by diffusion?

Answer 12

Something produced in cell e.g steroid hormones and fat soluble vitamins

To get rid of waste products

If cell is infected by a pathogen / cancerous - need to get a drug across the membrane! (Needs to be lipophilic therefore, quickest method is diffusion)

Question 13

What principles govern free movement across the membrane?

Answer 13

Molecular weight - less than 500 Da
Needs to be lipid if moving by diffusion, if not lipid based then it needs a carrier or channel protein
High concentration outside and low concentration inside membrane for diffusion
No more than 5 hydrogen bond donors and no more than 10 acceptors
Low overall charge

Question 14

Why do bacteria such as E Coli do NOT have cholesterol in their cell membrane?

Answer 14

Because they have a cell wall! It is the first like of defence
It acts like a cell membrane does in mammalian cells - they need cholesterol for fluidity and rigidity otherwise membrane would be disrupted

Question 15

What is an antibody and what are the parts of it?

Which part of the antibody binds to Specific sequence?

Answer 15

A Y-shaped protein produced by B cells / B lymphocytes. The mature B lymphocytes called plasma cells.

The variable regions (heavy or light) are specific to the antigen -in every case will recognise a different protein.

Fab regions are specific

Question 16

What is fluorescence?

How do we detect fluorescence?

Answer 16

It’s a type of electromagnetic radiation usually in form of light that’s caused by exciting a source. You give it energy and it emits light at a slightly different frequency.
Needs a constant stimulation / energy.

Use detector at specific wavelength

Question 17

How do we visualise the binding of antibodies to their target?

Answer 17

Have spectrum from purple - red of visible light.
Dyes are used attached to end of antibody and are excited by specific wavelength
E.g Alexa 568 is excited at 568nm BUT it emits light closer to 580nm so detector will need to detect 580nm.

Question 18

What does amphipathic mean?

Answer 18

Part of the molecule is hydrophilic and another part is hydrophobic

Question 19

What does conjugation mean?

Answer 19

Formation of a link between an amino acid and a waste or toxic product

Question 20

What does emulsification mean?

Answer 20

The mixing of 2 liquids that are usually unmixable

Question 21

What does hydrophilic mean?

Answer 21

Attracted to Aqueous substances

Question 22

What does hydrophobic mean?

Answer 22

Attracted to fats

Question 23

What does hydrogen bond mean?

Answer 23

Intermolecular force that forms dipole dipole attraction when hydrogen atom bonded to strongly electronegative atom exists in vicinity of another electronegative atom with lone pair of electrons

Question 24

What does cholestasis mean?

Answer 24

Decreased flow of bile due to impaired secretion by hepatocytes or obstruction

Question 25

What does polar mean?

Answer 25

A molecule where the distribution of electrons between covalently bonded atoms is NOT even causing a slight negative and positive charge to that atom

Question 26

What is a steroid?

Answer 26

Lipid containing a 4 ringed ridged structure

Question 27

What is a disulphide bridge / bond?

Answer 27

A reaction between sulfhydryl side chains of 2 cysteine residues One S anion acts as a nucleophile attacking the side chain of a 2nd cysteine

Question 28

What is a lipoprotein?

Answer 28

Any group of soluble proteins that combine with and transport fat or other lipids in the blood plasma

Question 29

What is the log P value?

Answer 29

A measure of the preference of a compound to dissolve in either water or an organic solvent (such as Octanol) when uncharged

Question 30

What is a ligand?

Answer 30

A molecule or ion that binds to another (usually larger) molecule causing a change in function

Question 31

What does de novo mean?

Answer 31

Newly generated

Question 32

What is a lipid raft?

Answer 32

Dynamic assemblies of proteins and lipids that float freely within the bilayer of the plasma membrane

Question 33

What is a Michelle?

Answer 33

Roughly spherically shaped grouping of amphiphillic molecules contained in a liquid.

Question 34

How does cholesterol effect fluidity for saturated and unsaturated fatty acids?

Answer 34

Saturated - cholesterol decreases fluidity Unsaturated - cholesterol increases fluidity, pushes FA apart because of 30 degree kink in tail

Question 35

What type of secondary structure of protein are necessary for the generation of large channel proteins?

Answer 35

Beta pleated sheets

Question 36

Membrane proteins can be attached to the phospholipid bilayer by a fatty acid chain. What is the reason for this?

Answer 36

Maintain the presence of the protein close to a transmembrane protein within a lipid raft. This can enhance cellular signalling and the protein may be present on either side of the membrane.

Question 37

What properties does transmembrane proteins possess?

Answer 37

N- or C- terminal ends of the protein contain amino acids that mediate protein protein interactions that will allow the accessory protein to support ligand binding. Protein protein interactions will enable shape stabilisation or a change that enables ligand binding. Accessory proteins are usually tethered to the membrane by carbohydrate linkers.

Question 38

What is essential for the interaction with the extracellular matrix.

Answer 38

Glycoprotein E.g. proteoglycans

Question 39

Lipoproteins are a … molecule with a layer of phospholipids around the … also containing … In the centre you’ve got cholesterol esters and … In the outer membrane you’ve got an … which is essential for … to work.

Answer 39

Spherical Outside Cholesterol Triglycerides Apolipoprotein Lipases

Question 40

One of Lipinski’s rule of 5 is High lipophicility (expressed as p value less than 5) What is this an estimate of?

Answer 40

Used as an estimation of the molecules ability to passively diffuse across the lipid membrane.

Question 41

What causes the ‘kink’ in unsaturated fatty acids?

Answer 41

The carbon carbon double bond induces a 30 degree bend which is known as the kink.

Question 42

What are liver cells called? What organelles are important for metabolic activity? What organelles are important for removing waste products?

Answer 42

Hepatocytes Mitochondria Smooth ER - contains enzymes required for detoxification.

Question 43

The plasma membrane has a high fluidity and few van der waals forces, but why is it thin?

Answer 43

Saturated long chain fatty acid tails extend longer than unsaturated with the 30 degree kink, and therefore membrane is thinner.

Question 44

The … synthesis of cholesterol takes place in the … using acetyl CoA together with the enzyme … which serves as the rate limiting step

Answer 44

De novo Liver HMG CoA reductase

Question 45

Bile acids are integral to the metabolism of … Due to their … nature they can solubilise hydrophobic fats by forming small fat droplets known as … This is known as … and significantly increases the surface area that … can work on.

Answer 45

Dietary fats Amphiphilic Micelles Emulsification Intestinal lipases

Question 46

What are the differences between flow cytometry and confocal microscopy?

Answer 46

Cells going in the flow cytometer can be in a suspension WHEREAS those on the microscope slide need to be attached or squashed on to the microscope slide. Means blood cells are perfectly suited to analysis by flow cytometry: erythrocytes, leukocytes, lymphocytes. They are already in a suspension! Confocal microscope: much more detailed, can actually see the structures. But it is only qualitative. Confocal microscope can tell if target is on top, bottom, inside or outside cell. Can’t tell that with cytometer. In common: both need lasers and detectors Analysis of cells: slow process in microscope. With cytometer takes a few seconds to analyse a thousand cells! Much faster.

Question 47

How does the membrane change during apoptosis? And it’s integrity ad a result of this? Apoptosis = programmed cell death

Answer 47

Membrane blebbing - tiny accidental pinching off of the membrane (loss). Cytosol is in there too as well as some nuclear content maybe if nucleus isn’t functioning. Shrinking of the nucleus and organelles Phosphatidylserine on outside - would change charge of cell membrane Condensation of chromatin, nucleus Vast amount of calcium in cytoplasm, KEY as it turns on scramblase which allows phos. Serine to be on outside of cell. Scramblase only enzyme active at this point! Loss of integrity = disintegration

Question 48

What is flow cytometry?

Answer 48

A multi parametric analysis tool, uses lasers and detectors. Signals are converted into electrical signals. Computer analysis Uses a cell suspension

Question 49

What are the advantages / disadvantages of flow cytometry vs confocal microscopy?

Answer 49

Provides faster analysis, accurate (as long as it is a single cell at a time), quantitative, less human error Expensive, less detailed, prone to technical problems, can’t see qualitative picture of cell, needs specialised operator

Question 50

Examples of signalling pathways

Answer 50

Caspases cascade (proteolytic cascade) Any homeostatic mechanism - anything with a feedback mechanism

Question 51

How can we ensure transmission is effective for cell signalling?

Answer 51

Lipid raft to keep things close together and parts that are not needed separate Support around receptor to receive signalling: Scaffolding Complex formation Docking sites

Question 52

What are the 4 common intracellular secondary messengers?

Answer 52

Cyclic AMP - activates protein kinase A Cyclic GMP - activates protein kinase G and opens cation channels in rod cells DAG - activates protein kinase C IP3 - opens Ca2+ channels in ER > Ca2+ levels increase > nearby proteins activated

Question 53

To respond to a signal, a cell must have a… molecule that can defect the signal

Answer 53

Receptor

Question 54

A molecule that binds to the particular 3D structure of a receptor is known as what?

Answer 54

Ligand

Question 55

When a protein, amino acid or peptide ligand binds to its specific receptor…

Answer 55

A second messenger molecule is activated Intracellular proteins form a cascade of events that lead to generation of secondary messengers cAMP, cGMP, IP3 or DAG

Question 56

When are G proteins active?

Answer 56

When GTP is bound When GTP is bound there is a change in shape that enables the breakup of a, b and y subunits to disassemble from one another and be present in an active form

Question 57

What is FALSE about plasma membrane G protein receptor signalling?

Answer 57

G protein alpha subunit Ga is inactive when bound to GTP the binding of GTP to the a subunit needs to happen for it to become activated!

Question 58

Why do some ligands trigger a second message?

Answer 58

The first messenger cannot cross the membrane! For the message to be passed on there is a need for participants of the cascade on both sides of the membrane

Question 59

What type of receptor catalyses phosphorylation of target protein?

Answer 59

Kinase

Question 60

ALL cell signalling involves which of the following?

Answer 60

A change in receptor shape Shape change happens regardless of ligand, receptor type or otherwise

Question 61

Steroid hormones activate a cell by what mechanism?

Answer 61

Binding to a receptor within the cell CYTOPLASM Steroid hormones are synthesised from cholesterol, containing the ridged sterol ring structure So are able to move across the cell membrane WITHOUT needing to be transported by a protein or move through a channel

Question 62

Ligand gated ion channels are specific for which of the following?

Answer 62

The ligand and the ion type The ligand must bind specifically to the receptor and the channel will only allow specific ions through depending on the selectivity filter

Question 63

Not all cells respond to a given endocrine signal because…

Answer 63

They do not have a specific receptor for the signal The receptor as a detector is required otherwise the cell does not know what the signal means!

Question 64

Hormones cause multiple responses by…

Answer 64

Using multiple receptors Causing different cellular responses

Question 65

What hormone is NOT derived from cholesterol?

Answer 65

Adrenaline

Question 66

What is a primary bile acid example?

Answer 66

Cholic acid

Question 67

What is required for the movement of phospholipids between inner and outer leaflet of plasma membrane?

Answer 67

ATP Flippase and floppase use ATP to move phospholipids between leaflets

Question 68

What does Annexin V bind to?

Answer 68

Phosphatidyl serine

Question 69

Flow cytometry graph: cells in the lower right quadrant are in early apoptosis What does this tell you?

Answer 69

Annexin V staining indicates phosphatidyl serine is present on surface but ATP is still being generated so propidium iodide is still being exported from cell

Question 70

What is the role of Scramblase in programmed cell death known as apoptosis?

Answer 70

It is activated by Ca2+ and exports phosphatidyl serine to outer leaflet

Question 71

Which of the coloured coat proteins represents Clathrin?

Answer 71

Green Clathrin is used for bud formation from the Golgi moving to early endosome and lysosome

Question 72

What is the role of scramblase at the plasma membrane?

Answer 72

It moves phospholipids between the inner and outer leaflet of a phospholipid bilayer in an indiscriminate manner

Question 73

Propidium iodide is a vital step detected by fluorescence flow cytometry In live cells…

Answer 73

It is excluded in an ATP dependant manner by intact membrane

Question 74

What is cleavage?

Answer 74

The splitting or severing of something

Question 75

What are GTPases?

Answer 75

Enzymes that catalyse the hydrolysis of GTP guanosine triphosphate to GDP guanosine diphosphate

Question 76

What is a kinase?

Answer 76

Proteins that generally add a phosphate (PO42 also known as phosphoryl groups) to proteins at specific amino acids Eg. Serine kinases add phosphate groups at serine amino acids

Question 77

What are phosphatases?

Answer 77

An enzyme that removes a phosphate group from a protein

Question 78

What is phosphorylation?

Answer 78

The addition of a phosphate PO42- to molecules

Question 79

What is a receptor?

Answer 79

A molecule in the cell membrane which responds specifically to a particular signal (ligand)

Question 80

What is a structural motif?

Answer 80

Short segments of protein 3D structure which are spatially close but not necessarily adjacent in the sequence

Question 81

What methods could we use to fura 2 dye with?

Answer 81

Flow cytometry Fluorescence Confocal microscopy Spectrophotometry

Question 82

The liver has got large volumes of… not only because the ER is the place where you generate … but also because it is the house for all those metabolic enzymes that are going to start … components which is a key … of the liver

Answer 82

Endoplasmic reticulum Lipids Detoxifying Function

Question 83

Erythrocytes needs to be able to move around the body at high speeds, therefore they need strength in their … They have an ankyrin and spectrin … behind them and large volumes of … because they need to have lipid rafts for the mesh to … through those band 3 proteins into the membrane. Hepatocytes do not have large volumes of cholesterol in them because they need a nice … membrane as they don’t need to move fast around body. They require a lot more … in the membrane I.e. protein channels with a selectivity filter. Needs things in membrane that regulate …

Answer 83

Membrane Mesh Cholesterol Attach Fluid Proteins Movement

Question 84

Foregut metabolisers (eg cows) have bacteria in the foregut that convert glucose into volatile fatty acids. What are the potential advantages?

Answer 84

The bacteria produce vitamins and amino acids that the cow can utilise The cows foregut contains bacteria that secret Cellulase The bacteria can remove toxins

Question 85

What tissue stores Glycogen and uses it to maintain normal blood glucose levels in the fasting phase?

Answer 85

Liver

Question 86

Foregut metabolisers (eg cows) have bacteria in the foregut that metabolise cellulose and glucose. What is the main DISadvantage for the cow?

Answer 86

The cows have to convert the volatile fatty acid (products of the bacterial glucose metabolism) into glucose via gluconeogenesis

Question 87

The erythrocytes produce lactate. Why?

Answer 87

They lack mitochondria, therefore cannot undertake aerobic glycolysis

Question 88

The monosaccharide Sorbitol is converted into Fructose by the enzyme…

Answer 88

Sorbitol dehydrogenase

Question 89

What compounds contain alpha 1-6 glycosidic bonds?

Answer 89

Glycogen Amylopectin

Question 90

What is an example of an Antiport System?

Answer 90

Na+ K+ ATPase

Question 91

What glucose transporter is reversible?

Answer 91

GLUT 2

Question 92

Anaerobic metabolism of glucose is important under what conditions?

Answer 92

Anaerobic bacteria Exercising muscle (oxygen limitation) Hypoxia (humna, eg heart attack) Ethanol metabolism (yeast) Some cancers

Question 93

Uptake of glucose from the intestinal lumen (under conditions where glucose concentrations in the lumen are low) requires energy. What drives this process?

Answer 93

Electrical potential Na+ K+ ATPase Chemical potential

Question 94

What glucose transporter is found in the endoplasmic reticulum?

Answer 94

GLUT 7

Question 95

What glucose transporter is activated by Insulin action?

Answer 95

GLUT 4

Question 96

Humans CANNOT digest cellulose because…

Answer 96

The intra molecular hydrogen bonds in cellulose make it water insoluble Cellulose contains Beta 1-4 glycosidic bonds They lack Cellulase

Question 97

What tissues can store glycogen?

Answer 97

Liver Skeletal muscle

Question 98

The enzyme pyruvate kinase is the FINAL control point in glycolysis. Why is this beneficial?

Answer 98

Want to prevent a futile cycle because it utilises energy! (Useless) Cycle: pyruvate > oxaolacetate, activated by hormone glucagon. Oxaloacetate > PEP is activated by hormone glucagon. PEP > pyruvate controlled by hormone insulin! If we REMOVE this step, we remove the futile cycle! Which is why pyruvate kinase is the final control point!

Question 99

Pathophysiology of type 1 diabetes mellitus

Answer 99

Autoimmune insulitis Inflammation more aggressive in young children than adults

Question 100

Epidemiology of type 1 diabetes mellitus

Answer 100

Most common form of diabetes in children Continues to present through decades but submerged by incidence of type 2 diabetes

Question 101

How can you differentiate between the major types of diabetes mellitus?

Answer 101

Clinical features Islet cell antigen autoantibody titres gradually wane Type 1 diabetes genetic risk score Assess endogenous insulin secretion by testing C peptide in people using insulin therapy

Question 102

What are symptoms of new onset Type 1 diabetes mellitus?

Answer 102

Collapsed, previously well Severely dehydrated Confused Short of breath but normal arterial pO2 K+ levels increased Glucose levels increased = diabetic B OH butyrate levels increased = keto pH levels decreased = acidosis

Question 103

Pathophysiology of type 2 diabetes

Answer 103

Insulin resistance Pancreatic beta cells respond but not enough… And high blood glucose gradually damages them!

Question 104

Autoimmune insulitis in type 1 diabetes differs with …

Answer 104

age of onset

Question 105

What is diabetes mellitus?

Answer 105

Osmotic diuresis secondary to excessive blood glucose concentration

Question 106

What is type 1 diabetes mellitus?

Answer 106

Autoimmune destruction of pancreatic beta cells

Question 107

What is type 2 diabetes mellitus?

Answer 107

Insulin resistance leading to beta cell fatigue and gradual failure

Question 108

Islet cell antigen auto antibody positivity … gradually

Answer 108

Wanes

Question 109

Normal and abnormal blood glucose concentrations are…

Answer 109

Tightly controlled Insulin secretion responds rapidly to requirements in healthy individuals

Question 110

Endogenous vs exogenous insulin

Answer 110

Modifications to alter absorption and clearance allow approximately physiological replacement

Question 111

Diabetic keto acidosis pathophysiology

Answer 111

Absolutely insulin deficiency = profound lipolysis, gluconeogenesis and glycogenolysis Oxaloacetate consumed by gluconeogenesis, Acetyl CoA diverted from Krebs cycle Osmotic diuresis and metabolic acidosis induced gastrointestinal loss cause dehydration

Question 112

Hypoglycaemia

Answer 112

Whipple’s triad definition stretches beyond diabetes mellitus Much higher risk of hypoglycaemia in type 1 diabetes compared with other types of diabetes No endogenous insulin to switch off, glucagon response lost! Frequent exposure lowers threshold for adrenaline release = impaired awareness

Question 113

What is the level 1 hypoglycaemia definition?

Answer 113

Glucose < 4 mmol/ L = usually no need to report

Question 114

What is the level 2 hypoglycaemia definition?

Answer 114

Glucose <3 mmol/L = serious, clinically important hypoglycaemia

Question 115

What is the level 3 hypoglycaemia definition?

Answer 115

SEVERE hypoglycaemia = severe cognitive impairment requiring external assistance for recovery

Question 116

Basal secretion

Answer 116

Low concentration Persists during fasting

Question 117

Prandial secretion

Answer 117

Rapid Proportional to requirements Change in concentration sometimes order of magnitude or greater

Question 118

Endogenous insulin forms a hexamer around a Zn2+ ion

Answer 118

Hexamers dissociate into dimers Dimers dissociate into monomers Monomers are the active form

Question 119

Endogenous insulin secretion enters the liver …

Answer 119

Directly

Question 120

Exogenous insulin is … before entering target organs

Answer 120

Diluted

Question 121

In type 1 diabetes, mimicking … insulin secretion is difficult

Answer 121

Normal

Question 122

What are the rapid acting insulin analogues?

Answer 122

Insulin lispro Insulin aspart Insulin glulisine

Question 123

What is neutral protamine hagedorn (NPH)?

Answer 123

5:1 human sequence insulin: protamine and zinc Protamine stabilises insulin crystals Injected as a suspension Thorough mixing essential prior to administration Absorbed slowly from subcutaneous depot High dose to dose variability

Question 124

What is the long acting insulin analogue that precipitates?

Answer 124

Insulin glargine

Question 125

What are the long acting insulin agonists that bind to albumin?

Answer 125

Insulin detemir Insulin degludec

Question 126

What is the route of endogenous insulin?

Answer 126

Hepatic portal vein > liver > ACTION

Question 127

What is the route of exogenous insulin?

Answer 127

Systemic veins > pulmonary circulation > dilution > liver > ACTION

Question 128

Human insulin forms:

Answer 128

Hexamers > dimers > monomers

Question 129

Rapid acting insulin analogues are …

Answer 129

Monomeric

Question 130

Long acting insulin’s exhibit delayed … and + or - clearance from blood

Answer 130

Absorption

Question 131

Dose to dose variation in effect is …

Answer 131

Undesirable

Question 132

Diagnosing diabetic keto acidosis : symptoms?

Answer 132

Lethargy Weakness Vomiting Abdominal pain Confusion Coma Kussmaul respiration

Question 133

Diagnosing diabetic keto acidosis:

Answer 133

Ketonaemia >3 mmol/L or significant ketonuria (more than 2+ on standard urine sticks) Blood glucose > 11 mmol/L or known diabetes mellitus Serum bicarbonate <15 mmol/L and or venous pH <7.3

Question 134

Diabetic keto acidosis treatment priorities:

Answer 134

1. Correct dehydration - intravenous fluids 2. Switch off keto genesis - intravenous insulin 3. Prevent life threatening hypokalaemia - add potassium to intravenous fluid 4. Prevent it happening again - identify cause, correct and educate

Question 135

What is whipples triad?

Answer 135

Characteristic symptoms and / or signs occur in fasting state Confirmation of low blood glucose by reliable assay Resolution with administration of glucose

Question 136

In type 1 diabetes, hypoglycaemia is an … occurrence There is an impaired … response There is an impaired … of hypoglycaemia

Answer 136

Everyday Counter regulatory hormone Awareness

Question 137

What is gluconeogenesis?

Answer 137

The synthesis of glucose from NON carbohydrate substrates It’s a fasting response pathway (4-6 hours after meal) Driven by hormone glucagon

Question 138

What is the first effect of glucagon?

Answer 138

It initiates the breakdown of the Liver glycogen to release glucose into bloodstream Main purpose of that is to prevent hypoglycaemia Allows neural tissues and RBCs to function normally

Question 139

How much glycogen is in the liver?

Answer 139

200g - so the secondary response is gluconeogenesis!

Question 140

What cells is glucagon secreted by?

Answer 140

Pancreatic alpha cells

Question 141

What is the initial substrate for gluconeogenesis?

Answer 141

Pyruvate Some will be formed from lactate. Lactate dehydrogenase converts lactate > pyruvate

Question 142

What are glucogenic amino acids?

Answer 142

Once amino acids have been broken down the amino group has been removed, they can then be utilised as intermediates or substrates for gluconeogenesis

Question 143

What 2 tissues is glucose released from in gluconeogenesis?

Answer 143

The liver and kidneys Both of these have the GLUT 2 transporter which is bi directional - can take up or release glucose

Question 144

Glycerol is another substrate for gluconeogenesis. What is it produced by?

Answer 144

Hydrolysis of triglycerides in adipose tissue Hydrolysis releases 2 products: glycerol and unesterified fatty acids (free FA)

Question 145

What happens under starvation conditions?

Answer 145

Fatty acids are taken up by the liver and kidneys and they are beta oxidised to Acetyl CoA.

Question 146

What is the advantage of beta oxidation?

Answer 146

Produces NADH and FADH2 - both of which can be used to make ATP in oxidative phosphorylation

Question 147

What happens when there is a surplus of Acetyl CoA?

Answer 147

Converted into ketone bodies - a secondary source of energy for brain / RBC / muscle tissues

Question 148

What is glycolysis?

Answer 148

Glucose > pyruvate Driven by insulin

Question 149

What is gluconeogenesis?

Answer 149

Pyruvate > glucose Driven by glucagon

Question 150

What are the 3 control points / uni directional enzymes in glycolysis?

Answer 150

Hexokinases PFK1 Pyruvate kinase

Question 151

The 3 uni directional steps in glycolysis need to be … in gluconeogenesis by specific enzymes

Answer 151

Bypassed

Question 152

When can gluconeogenesis take place?

Answer 152

When there’s an energy rich environment Utilises ATP and GTP from krebs. Oxidative phosphorylation is the main pathway for ATP generation

Question 153

What are precursors for gluconeogenesis?

Answer 153

Pyruvate Lactate Oxoaloacetate Amino acids

Question 154

Animals CANNOT convert fatty acids into … Plants, yeast and many bacteria can convert … into glucose

Answer 154

Glucose Fatty acids

Question 155

Why are fatty acids required in gluconeogenesis?

Answer 155

Their breakdown provides the energy to drive the process

Question 156

What is anoplerisis?

Answer 156

Infusion of amino acids that is used to make new compounds

Question 157

What 3 locations does gluconeogenesis take place?

Answer 157

Mitochondria ER Cytosol

Question 158

Glycolysis only takes place in the …

Answer 158

Cytosol

Question 159

What is the co factor biotin derived from?

Answer 159

A B vitamin

Question 160

Oxaloacetate is the … in gluconeogenesis

Answer 160

1st intermediate

Question 161

Oxaloacetate CANNOT be exported from mitochondrion. How do cells deal with this?

Answer 161

They convert oxaloacetate to Malate and then in the cytosol, convert malate back to oxaloacetate

Question 162

What is the advantage of converting oxaloacetate to malate?

Answer 162

Can transfer reducing equivalents (electrons) from inside mitochondrion to the outside Electron donor in mitochondrion is NADH and electron acceptor in cytosol is NAD+ So can make NADH in cytosol using oxaloacetate as a starting point

Question 163

The 2nd regulated step in gluconeogenesis is the …

Answer 163

Start point of gluconeogenesis in the cytosol

Question 164

How is F26BP a regulator?

Answer 164

It is an allosteric activator of PFK1 and an inhibitor of FBPase 1

Question 165

What is F26BP formed by?

Answer 165

The enzyme / bi functional protein PFK2 / FBPase 2

Question 166

What is the PFK2 / FBPASE 2 bi functional protein?

Answer 166

Has a serine in regulatory region that can be phosphorylated or de phosphorylated - either activating a kinase or phosphatase domain Serine regulation controlled by glucagon or insulin

Question 167

How is AMP an allosteric inhibitor of FBPase 1?

Answer 167

High levels of AMP indicate low energy status of the cell - need to replenish ATP levels before gluconeogenesis can continue One way ATP levels can be replenished is by beta oxidation of fatty acids

Question 168

What happens when there’s high levels of F26BP?

Answer 168

Insulin Stimulates glycolysis, inhibits gluconeogenesis PFK2 active FBPase 2 inactive

Question 169

What happens when there’s low levels of F26BP?

Answer 169

Glucagon - ^ [cAMP] Inhibits glycolysis, stimulates gluconeogenesis PFK2 inactive FBPase2 active

Question 170

PKK 1 converts F6P into … It is allosteric ally activated by F26BP

Answer 170

F16BP

Question 171

What happens to the produced glucose?

Answer 171

Goes back into cytosol and can get transported out of the cell using GLUT 2 transporter found in plasma membrane

Question 172

Glucose 6 phosphate CANNOT get out of the cell, why?

Answer 172

Because the GLUT transporters are specific for monosaccharides and G6P is not one! This is the reason for phosphorylating glucose > G6P, to trap it inside the cell

Question 173

How is G6P transported out of the cell?

Answer 173

The glucogenic tissues, the liver and kidneys, both have the reversible GLUT 2 transporter It CANNOT transport G6P, only glucose So G6P is converted to glucose to transport it out

Question 174

How is G6P transported into ER lumen?

Answer 174

Via a specific G6P transporter

Question 175

Glucose 6 phosphate is the enzyme that … the Hexokinase step in glycolysis It is inside the … lumen

Answer 175

Bypasses ER

Question 176

Where does the Cori Cycle take place?

Answer 176

In vigorously exercising muscle tissues that produce lactate. Lactate converted to pyruvate by lactate dehydrogenase Pyruvate converted to glucose by gluconeogenesis Glucose then exported back to muscle tissue for utilisation Gl

Question 177

How does adrenaline control the cori cycle?

Answer 177

Fight or flight hormone It induces glycolysis in muscle tissue and gluconeogenesis in liver tissue

Question 178

What is the glucose alanine cycle?

Answer 178

Decreasing the formation of lactate through the conversion of pyruvate to the amino acid Alanine. Alanine is transported to the liver where amino group is removed to become pyruvate Pyruvate then used to make glucose in gluconeogenesis

Question 179

What are the 2 glucose sparing pathways?

Answer 179

Cori Cycle Glucose Alanine Cycle

Question 180

What is the purpose of the 2 glucose sparing cycles?

Answer 180

Used by skeletal muscle and liver to spare glucose for the brain and red blood cells

Question 181

The Cori Cycle: Muscle

Answer 181

ATP produced by glycolysis for rapid contraction

Question 182

The Cori Cycle: Liver

Answer 182

ATP used in gluconeogenesis during recovery

Question 183

What are normal blood glucose levels?

Answer 183

4-6 MM

Question 184

What are the 2 amino acids that are unable to furnish carbon for net glucose synthesis?

Answer 184

Leucine and lysine

Question 185

The first gluconeogenic steps travel through the …

Answer 185

Mitochondrion

Question 186

What are the 4 regulated steps that bypass the 3 irreversible enzymes in glycolysis?

Answer 186

1. Carboxylation of pyruvate > oxaloacetate OAA 2. Decarboxylation of cytosolic OAS > PEP 3. De phosphorylation of F16BP > F6P 4. De phosphorylation of G6P > glucose

Question 187

What does a reversible enzyme mean?

Answer 187

The direction of the reaction is driven by the relative amount of substrate and product

Question 188

What are control points?

Answer 188

They affect the rate of the WHOLE pathway but they are NOT rate limiting steps

Question 189

What is the Preparatory Phase of Glycolysis?

Answer 189

The phase that utilises ATP, it requires energy

Question 190

What direction do reversible reactions go in?

Answer 190

High - low

Question 191

How does the Payoff Phase in glycolysis generate energy?

Answer 191

ATP by substrate level phosphorylation Reduction of NAD+ to NADH

Question 192

How do we know that Galactose (converted to glucose) requires energy?

Answer 192

There’s an intermediate called UDP galactose which is derived from UTP - and UTP is an energy molecule

Question 193

Trehalase is a plant based 2 glucose molecule. How is it different to Maltose?

Answer 193

Difference is in the carbons bonded together to make glycosidic bond

Question 194

What are the 2 ways that Fructose can enter Glycolysis?

Answer 194

By being converted to F6P or by being converted to glyceraldehyde and dihyoxyacetone phosphate DHAP

Question 195

What is the full conversion of glucose > CO2

Answer 195

Respiration Aerobic conditions

Question 196

What are the fates of pyruvate?

Answer 196

Alanine VFA Acetyl CoA (citric acid cycle) Oxaloacetate (krebs / gluconeogenesis) Ethanol + CO2 - the CO2 used in food production for carbonated drinks and making bread Lactate

Question 197

What are the 2 conditions where oxaloacetate is produced from pyruvate?

Answer 197

Under conditions of gluconeogenesis - substrate lactate > pyruvate > oxaloacetate Under conditions of high insulin (glycolysis) - pyruvate > oxaloacetate which can be used to make citrate for TCA cycle

Question 198

How do we control how much pyruvate is converted to Acetyl CoA and how much is converted to oxaloacetate?

Answer 198

A build of Acetyl CoA inhibits further formation of it from pyruvate and activates the conversion of pyruvate > oxaloacetate So inhibition or activation controls the amounts of Acetyl coa or oxaloacetate - helps drive the cycle!

Question 199

What is Acetyl CoA used for?

Answer 199

Intermediate in TCA cycle Replenishes ATP stores in cell Then used for synthesis in the cytosol - fatty acid and cholesterol synthesis (the two endpoints for Acetyl CoA)

Question 200

What conditions can Acetyl CoA build up occur? Ie. Start inhibiting pyruvate dehydrogenase complex

Answer 200

Anaerobic conditions (low oxygen) - inhibits oxidative phosphorylation, build up of NADH and FADH2, inhibits Krebs, get build up of Acetyl CoA Fasting conditions (more than 8 hours after last substantial meal) - lipolysis releases fatty acids, transported to liver where they are beta oxidised, an end product is Acetyl CoA. Acetyl CoA allosteric ally activates pyruvate carboxylate - ^ oxaloacetate, which is used for gluconeogenesis

Question 201

Could argue that we Need … amounts of oxaloacetate and acetyl CoA to allow … to be formed and for TCA cycle to …

Answer 201

Equivalent Citrate Continue

Question 202

Why is MORE Acetyl CoA made in the Citric acid / Krebs cycle than oxaloacetate?

Answer 202

Due to Anabolic compounds - they replenish intermediates in the Krebs cycle

Question 203

What is the glucose sparing effect in the Cori Cycle?

Answer 203

Glucose can be exported back to muscle tissue and be reused / re utilised

Question 204

How much glucose does the brain need to keep it going?

Answer 204

130g in 24 hours

Question 205

Why is glucose needed for vigorous exercise?

Answer 205

As glucose is metabolised much faster than fatty acids, although energy output is lower

Question 206

Why can’t humans sprint long distances?

Answer 206

They’ve used up all their glycogen and glucose

Question 207

Can blood cells oxidise fatty acids?

Answer 207

No!

Question 208

Cori Cycle: Intra muscular glycogen is the … source of glucose under vigorous exercise / rapid contraction … Glycogen broken down to glucose by hormone … Glucose converted to … through glycolysis Oxygen is … Almost all pyruvate is converted to …

Answer 208

Initial Conditions Adrenaline Pyruvate Limiting Lactate

Question 209

What is the advantage of the glucose alanine cycle?

Answer 209

Reduces the production of lactate, decreases pH of tissues, decreases the output of that tissue that may cause damage

Question 210

Acetaldehyde is the compound that causes …

Answer 210

Hangovers

Question 211

How is Disulfiram used to treat alcoholics?

Answer 211

It inhibits the enzyme acetaldehyde dehydrogenase > build up of acetaldehyde So if an alcoholic is treated with this and they drink alcohol > build up of acetaldehyde > semi permanent hangover Meant to stop them drinking

Question 212

Humans, ethanol fermentation: we do NOT have the pyruvate carboxylase enzyme, so what happens?

Answer 212

If theres an excess of ethanol, it is converted into acetaldehyde using enzyme in liver called alcohol dehydrogenase Acetaldehyde converted into Acetyl CoA using 2nd enzyme called acetaldehyde dehydrogenase

Question 213

In healthy individuals, there’s a peak in plasma glucose concentration after each meal. How is this mediated by Insulin?

Answer 213

Insulin is secreted from pancreatic beta cells. Function is to remove glucose from blood > preventing glycation of blood vessels, haemoglobin and proteins in eyes

Question 214

What are the 3 metabolic control points in Glycolysis?

Answer 214

Phosphorylation of glucose Formation of F16BP Formation of pyruvate

Question 215

What are the roles of ATP?

Answer 215

Donate an inorganic phosphate Provide energy to drive reactions from left to right - energy is provided by hydrolysis of phosphodiester bond in ATP

Question 216

What are Isoenzymes?

Answer 216

Enzymes with an identical function that are produced from different gene products Have different tissue expression snd different kinetic properties

Question 217

Hexokinase 1

Answer 217

Most tissues (ubiquitous) Broad specificity - in terms of 6 carbon monosaccharides Low Km - high affinity for monosaccharides Product inhibition - glucose 6 phosphate is an inhibitor of enzyme Hyperbolic kinetics - Michaelis Menten

Question 218

Hexokinase 4 (glucokinase)

Answer 218

Liver, pancreas Biosensor in Beta cells Broad specificity High km, low affinity High Vmax Sigmoidal kinetics - cooperativity - different active sites work together Allosteric control - glucose and F6P REGULATION by Insulin

Question 219

How does glucokinase act as biosensor?

Answer 219

Acts as a glucose sensor for high blood glucose concentrations - > 6 MM which would = Hyperglycemia Glucokinase phosphorylates the glucose taken up to cause the secretion of insulin

Question 220

The liver is the 1st tissue that dietary sugars will reach. What are those blood sugars used for?

Answer 220

Replenish ATP levels Replenish glycogen Convert into FA and cholesterol

Question 221

What is the purpose of glucokinase in reacting to hyperglycemia?

Answer 221

Decreases the high glucose concentration by insulin secretion and metabolism

Question 222

At what glucose concentration is Hexokinase 1 fully saturated due to its low km?

Answer 222

5MM - means it is always saturated under feeding or fasting conditions! It is working at full capacity

Question 223

Hexokinase 1 is fully saturated at normal glycemic concentrations and above but has a relatively low vmax. What does this mean?

Answer 223

It is active all the time but only takes up a small amount of glucose at 1 time. Takes up enough for brain to function but doesn’t take up excess!

Question 224

How is glucokinase regulated by Glucose Kinase Regulatory Protein GKRP?

Answer 224

It transports Hexokinase 4 from cytosol into nucleus where it is INACTIVE > glycolysis is inhibited

Question 225

How does the regulation of glucokinase by by F6P and glucose affect glycolysis?

Answer 225

F6P - allosteric inhibitor of glycolysis in terms of this enzyme Glucose - allosteric activator of glycolysis

Question 226

What are the group of isoenzymes that catalyse glycolysis control point 2?

Answer 226

Phosphofructokinases - PFK

Question 227

Why is glycolysis control point 2 an important control step?

Answer 227

The product F16BP is the 1st dedicated product in glycolysis, means that G6P can be converted into other pathways (glycogen synthesis, pentode phosphate pathway)

Question 228

What is PFK1 regulated by?

Answer 228

Substrate concentration of ATP, F6P Energy levels of ATP, citrate, ADP, AMP F26BP

Question 229

PFK 1 has 4 different subunits, each with a catalytic site and an allosteric site. What is the function of the catalytic sites?

Answer 229

Converts F6P into F16BP

Question 230

What isoenzyme is F26BP made by?

Answer 230

PFK 2 - it preferentially converts F6P into F26BP

Question 231

F26BP is hydrolysed back to F6P by…

Answer 231

FBPase 2 - fructobisphosphatase

Question 232

What does High ADP (low ATP) do to the activity of PFK 1?

Answer 232

It competitively displaces ATP from allosteric site. When ADP binds to site, it causes a conformational change that increases the activity of PFK 1

Question 233

F26BP is not used for any other purpose other than regulating the 2 enzymes…

Answer 233

PFK 1 and FBPase 1

Question 234

Why do cells make F26BP, as it has no direct metabolic advantage?

Answer 234

Insulin > PFK2 > increased F26BP > PFK1 > increased glycolysis

Question 235

What is anaerobic glycolysis and why is it beneficial?

Answer 235

Using up NADH to make NAD+ again Beneficial as it allows glycolysis to continue, can continue making ATP

Question 236

Step 10 in glycolysis

Answer 236

Uni directional Bypassed in red blood cells Net outcome is 2NADH and 2 ATP under aerobic conditions

Question 237

What are the allosteric inhibitors of pyruvate kinase?

Answer 237

Alanine - skeletal muscle, liver High levels of ATP - don’t need glycolysis to take place High levels of Acetyl CoA - fasting response - inhibits glycolysis Long chain fatty acids

Question 238

What is an allosteric activator of pyruvate kinase?

Answer 238

F16BP - an example of Feed forward control as it is made 6 steps prior to conversion to PEP

Question 239

What is pyruvate kinase deficiency? (Haemolytic anaemia)

Answer 239

Form of anaemia due to abnormal breakdown of red blood cells PK deficiency is the 2nd most common cause of enzymatic related haemolytic anaemia

Question 240

PK deficiency characteristics

Answer 240

Affects allosteric control and protein levels Abnormal Km or vmax Abnormal response to F16BP ALTERED enzyme activity, stability or concentration

Question 241

What is PK deficiency caused by?

Answer 241

Mutations at the gene levels - ie the DNA sequence

Question 242

What is the Warburg effect?

Answer 242

Where glycolysis takes place under anaerobic conditions. Found in some tumour cells

Question 243

What happens in tumours under the Warburg effect?

Answer 243

Do NOT have pyruvate going into mitochondria due to lack of oxygen Pyruvate is converted into lactate Uses up NADH produced in glycolysis and oxidises it back to NAD+

Question 244

What is the benefit of Warburg effect to the tumour cells?

Answer 244

They can use glucose as an energy source due to the substrate NAD+ which can be re utilised = glycolysis occurs at elevated rate

Question 245

What is the downside of the warburg effect in tumour cells?

Answer 245

Produce a lot less ATP per unit glucose

Question 246

The Warburg effect - the inhibition of glycolysis has been used to treat tumours. Examples?

Answer 246

Transcription factor HIF1 - hypoxia inducible factor It regulates gene transcription under low oxygen conditions (hypoxia)

Question 247

18F FDG is used in clinical conditions to detect … It contains 18F stable … and can use instruments to detect higher levels called …

Answer 247

Tumours Isotope PET scanners - positron emission tomography

Question 248

What are PET scanners and how do they work?

Answer 248

An analogue of glucose. Cells take it up thinking it’s glucose > converts it to G6P analogue > gets trapped in cells Glycolysis takes place at faster rate in tumours so there’s increased uptake of that compound > detected via PET scanner > red = high levels > eg in Brain

Question 249

What is the irreversible oxidative phase of pentose phosphate pathway?

Answer 249

Contains the controlling enzyme for PPP - there is only 1 control point!

Question 250

What is the reversible NON oxidative phase in pentose phosphate pathway?

Answer 250

Where unusual sugars are inter converted Controlled by insulin at level of transcription Utilises G6P as the starting substrate

Question 251

What are the 3 endpoints that glucose can enter a cell?

Answer 251

Pyruvate through glycolysis Glycogen storage (liver) Pentose phosphate pathway - synthesis / protection

Question 252

Pentose phosphate pathway

Answer 252

NOT for energy production - NO ATP or NADH produced Occurs in cytosol

Question 253

What specialised metabolic needs does pentose phosphate pathway cater for?

Answer 253

NADPH Ribose 5 phosphate Dietary pentose sugar metabolism Synthesis of aromatic amino acids

Question 254

What happens in the oxidative phase of the PPP?

Answer 254

G6P is oxidised and 2NADP+ is reduced to 2NADPH Catalysed by G6P dehydrogenase - the control point in ppp!

Question 255

Where does the PPP cycle take place?

Answer 255

Liver and adipose (fat) tissue

Question 256

What is the role of glucose 6 phosphate dehydrogenase in the PPP?

Answer 256

Primary point of regulation - it is the CONTROL POINT in ppp Converts NADPH to NADP+ NADPH: NADP+ ratio is 100:1 in the cell - high ratio! Insulin

Question 257

How is G6P dehydrogenase regulated in ppp?

Answer 257

By amount of NADPH that is formed relative to NADP+ in the cell. NADPH is product inhibitor of G6P D enzyme = high ratio in the cell Insulin - it regulates amount of G6P D enzyme at the level of transcription

Question 258

What is the metabolic effect of the NADPH : NADP+ 100:1 ratio?

Answer 258

It will only activate G6P D enzyme when NADPH levels are low! Normal conditions, will inhibit the enzyme and so PPP. This is so that energy is generated first so synthesis can proceed!

Question 259

What is the reason for the difference in structure between NADPH and NADH? (NADPH has extra phosphate group)

Answer 259

Means NADH is utilised by specific enzymes - eg in oxidative phosphorylation The phosphate group makes a difference in terms of binding to enzymes as there is stereo specific binding of ligand to enzyme active sites!

Question 260

What is the non oxidative phase in ppp?

Answer 260

The regeneration of G6P from R6P that occurs in the liver and adipose tissue

Question 261

Why does non oxidative phase of ppp take place in liver and adipose tissue?

Answer 261

Liver utilises NADPH for lipogenesis - fatty acid and cholesterol synthesis Adipose tissue utilises NADPH to synthesise FA which are converted to triglycerides = biggest storage form of energy from the diet!

Question 262

What is ribose 5 phosphate used for?

Answer 262

Synthesis of nucleic acids / nucleotides Specifically DNA / RNA as they are only made when cells divide - which requires high energy status

Question 263

What is erythrose 4 phosphate used for? (Ppp)

Answer 263

To make the aromatic amino acids - eg phenylalanine, tyrosine, tryptophan (Benzene ring like structures)

Question 264

What happens in FA synthesis and what do you need?

Answer 264

Add 2 carbons for every cycle taking place Need 2 NADPH to provide e- Acetyl CoA as a starting point

Question 265

What are the roles of NADPH?

Answer 265

Reductive biosynthesis (fatty acids) Reduction of hydrogen peroxide (GSH / GSSG) Cytochromes p450 Phagocytosis Synthesis of nitric oxide

Question 266

What are the 2 pathways where NADPH donating e- is important?

Answer 266

Fatty acid synthesis Cholesterol synthesis

Question 267

What is the role of NADPH in reductive biosynthesis?

Answer 267

Supplies reducing equivalents (donates electrons)

Question 268

Reduction of hydrogen peroxide: why can oxygen be a poison?

Answer 268

It can be reduced (addition of e-) to highly reactive intermediates - superoxide, hydrogen peroxide, hydroxyl radicals

Question 269

Humans have protective mechanisms to reduce the effect of oxygen radicals but they decline with age. What is the effect of the radicals?

Answer 269

Can modify proteins, lipids, nucleic acids Modified FA can change functionality of membranes Oxidised FA and cholesterol can cause Atherosclerosis - formation of atherosclerotic plaques - blockage of blood vessels that cause heart attacks!

Question 270

What are the 2 diseases that can be directly affected by oxygen free radicals?

Answer 270

Cancer and ageing

Question 271

What is oxidative stress?

Answer 271

When there is increased levels of free radicals Causes cancer and ageing

Question 272

What are the 2 protective me chains for oxidative stress?

Answer 272

1. Enzyme systems - superoxide dismutase SOD, catalase, glutathione peroxidase 2. Anti oxidant chemicals- Ascorbate, vitamin E, b carotene Vitamin C (ascorbate) is water soluble and vitamin E is hydrophobic B carotene is converted into vitamin A

Question 273

What does catalase do?

Answer 273

Breaks down H202 to oxygen and hydrogen (Metals as cofactors)

Question 274

What does superoxide dismutase do?

Answer 274

Breaks down superoxide intermediate into oxygen and hydrogen peroxide

Question 275

What is glutathione (GSH) peroxidase and what does it do?

Answer 275

A tri peptide made up of 3 AA Breaks down H202 to water. In the process it oxidises GSH (reduced glutathione) into the oxidised version GSSG

Question 276

Biologically active form: GSH - reduced glutathione

Answer 276

It has 3 AA: gammaglutamyl, cysts yk and glycine. IMPORTANT: it has a cysteine which has a reduced sulfhydryl group SH. 2 reduced GSH form 1 oxidised GSSG

Question 277

Biologically intert form: GSSG - oxidised glutathione

Answer 277

Oxidised glutathione is characterised by a disulphide bridge. The ratio of GSSG : GSH is an indicator of oxidative stress, the higher the ratio, the stronger the OS in the cell!

Question 278

How do we recycle GSSG back to GSH?

Answer 278

GSH reductase can reduce the disulphide bond in the GSSG to form 2 molecules of GSH GSH reductase requires NADPH as the cofactors that donates e-. Main source of that NADPH is the ppp!

Question 279

What is the main reason we need Selenium in the diet?

Answer 279

To decrease the levels of oxygen free radicals using the glutathione (GSH) peroxidase enzyme

Question 280

What is the Microsomal System?

Answer 280

Microsomes are purified ER Small vesicles that contain cytochrome p450 enzymes Used in drug metabolism (Xenobiotics)

Question 281

What are the 2 functions of cytochrome p450 in drug metabolism?

Answer 281

Convert hydrophobic drugs into hydrophilic products - to increase excretion of these compounds To specifically convert pro drugs into ACTIVE drugs - ie cancer drugs

Question 282

What are the 3 examples of the Mitochondrial System? (That use cholesterol as the substrate)

Answer 282

Steroids - hormones eg oestrogen, testosterone Bile acids - amphipathic, have a hydrophilic and hydrophobic component. Vitamin D - made in liver, skin and kidney

Question 283

What are the 2 roles of bile salts in the body?

Answer 283

Small intestine - act as biological detergents, help to solubilise dietary fats. This allows lipases to break down fats for them to be absorbed Main mechanism for getting rid of excess cholesterol - converted into bile salts which is excreted in small intestine through faeces

Question 284

What is the misconception regarding vitamin D?

Answer 284

The body started shutting down vitamin D synthesis after half an hour! So no point sitting in the sun all day

Question 285

What are the cytochrome p450 enzymes?

Answer 285

Group of enzymes that have a colour - they absorb light in the visible range All of them have a metal cofactors that provides the colour. Depends on the metal Eg if cytochrome p450 has iron in it, then it is normally a red colour

Question 286

What does the p450 part of cytochrome p450 mean?

Answer 286

Means that in the presence of carbon monoxide, this group of enzymes shows an absorbance peak at 450nm CO binds tightly to Fe containing proteins eg haemoglobin

Question 287

What 2 cofactors does cytochrome p450 utilise?

Answer 287

Oxygen NADPH - donates electrons

Question 288

Why is ROH much more reactive than RH?

Answer 288

Contains the nucleophile O2

Question 289

What is phagocytosis?

Answer 289

Breakdown of foreign compounds by macrophages, phagocytes etc Cell engulfs particle, digests it and expels the waste products

Question 290

What is the process of phagocytosis? (Oxygen independent system)

Answer 290

1. Lysosome mediated process - intracellular recycling plants, they fuse with vesicle. Have an acidic ph 2. Acidic ph - around 4.5. Specific enzymes. Acidic environment helps breakdown foreign compounds. 3. Proteolytic enzymes - break down proteins. + lipases and nucleases

Question 291

Process of phagocytosis/ oxygen dependant system

Answer 291

1. Oxygen dependant degradation depends on NADPH and production of reactive oxygen species 2. NADPH dependant oxidase generated hydrogen peroxide H202 3. Myeloperoxidase then generates hypochlorite OCL-. This is the active component of bleach

Question 292

The oxygen dependant process of phagocytosis actively forms oxygen free … in terms of …

Answer 292

Radicals Protection

Question 293

Why is nitric oxide required and why does it need to be made continuously?

Answer 293

Required for proper functioning of blood vessels Has a very short half life of around 3-10 seconds

Question 294

What does nitric oxide synthase do? Why does it need arginine and NADPH?

Answer 294

Converts oxygen to nitric oxide Arginine - donates the nitrogen NADPH - provides the e-

Question 295

What are the functions of nitric oxide?

Answer 295

Vasodilator - blood vessel dilation Protection against ischaemic damage Cardiovascular signalling molecule Neurotransmitter Prevents platelet aggregation - linked to Atherosclerosis Bactericidal - NO combine with a further oxygen to form anti bacterial compounds

Question 296

What is Wernicke Korsakoff Syndrome?

Answer 296

Memory disorder due to vitamin B1 (thiamine) deficiency (beriberi) - decreases uptake to lower than 10% of normal in the intestine Associated with alcoholism, malnutrition and thiamine transporter variants Damaged nerve cells Transletolase is a thiamine / vitamin B1 dependant enzyme in the PPP - requires it for full activity!

Question 297

What are inborn errors of metabolism due to?

Answer 297

Genetic modifications

Question 298

Why is transketolase important? (Wernicke korsakoff syndrome and PPP)

Answer 298

Need the enzyme to convert R5P back to G6P in the liver. This increases production of NADPH If we have a deficiency of thiamine cofactor, enzyme cannot function properly and NADPH production decreases. Effects nerve and neuro function

Question 299

Glucose 6 phosphate dehydrogenase deficiency:

Answer 299

Common - more than 209 million affected > 300 different mutations (polymorphisms) Characterised by haemolytic anaemia - RBCs break down faster than normal Small effect on life expectancy But gives resistance to malaria!

Question 300

What are polymorphisms?

Answer 300

Mutations at the gene level Can be silent (nothing happens), conservative (small effect), NON conservative (large effect, or truncation (stop codons etc)

Question 301

What is the main effect of G6PD deficiency?

Answer 301

At the level of erythrocytes, RBCs Leads to a lowered recycling of GSSG back to GSH - means individuals are susceptible to OS

Question 302

What are the 2 endpoints of G6PD deficiency in the RBCs?

Answer 302

Haemoglobin is denatured - as it contains reduced sulphydryls, can be detected in RBCs in the form of Heintz Bodies Oxidation of phospholipids - leads to haemolysis - breakdown of RBCs, releasing haemoglobin

Question 303

Why is G6P D deficiency common in RBCs?

Answer 303

In normal cells, there is the GSH peroxidase system that protects against O2 free radicals. People with the deficiency in G6P can only use the enzyme in PPP to convert NADP+ back to NADPH. If that level is decreased, the response is decreased. All other cells EXCEPT for erythrocytes have a backup enzyme system called NADP+ dependant malate dehydrogenase system

Question 304

What is the main function of the NADP+ dependant malate dehydrogenase system? Why do RBCs not have this system?

Answer 304

To transport pyruvate across the mitochondrial membrane RBCs do NOT have mitochondria so do NOT have this system

Question 305

Most individuals with G6PD deficiency are … There is no effect unless they are triggers called … They convert someone from asymptomatic to …

Answer 305

Asymptomatic Precipitating factors Symptomatic

Question 306

What are the precipitating factors in G6PD deficiency?

Answer 306

Oxidant drugs - antibiotics, antimalarials, antipyretics. They all increase oxidative potential in a cell. They can trigger haemolysis Favism - fava bean. Induces haemolysis Infection - phagocytosis produces H202 and hypochlorite. Both have high oxidative potential

Question 307

G6PD deficiency causes neonatal jaundice. What is this?

Answer 307

In babies liver has NOT fully developed, they struggle to breakdown haem, leads to increased levels of Bilirubin Causes neonatal jaundice, yellow colour due to high levels of haem Treatment is UV light - hydrolysis bilirubin and allows for excretion

Question 308

What does the phosphorylation of tyrosine residues within the kinase domain do?

Answer 308

Enhances kinase activity

Question 309

What does phosphorylation of tyrosine residues OUTSIDE of the domain do?

Answer 309

Generates high affinity docking sites for intracellular signalling molecules

Question 310

What is RAS GEF needed for? And what is GEF?

Answer 310

Needed for GTP or GDP exchange GEF = guanosine nucleotide exchange factor - GEF can activate RAS which is important for lots of activity

Question 311

What do activated signalling proteins do?

Answer 311

Relay signal downstream

Question 312

Ras family of monomeric GTPases function as a …

Answer 312

Molecular switch

Question 313

What do Ras GTPase activating proteins do?

Answer 313

Increase the rate of GDP hydrolysis by Ras itself (which will inactivate RAS)

Question 314

Why can active RAS induce the phosphorylation cascade?

Answer 314

As ras is a kinase

Question 315

RTKs can activate…

Answer 315

Ras

Question 316

Ras activates a cascade of mitogen activated kinases which includes:

Answer 316

RAF - MAP kinase kinase kinase (MAPKKK) Mek - MAP kinase kinase (MAPKK) Erk - MAP kinase (MAPK)

Question 317

What does a MAP kinase do?

Answer 317

Something that induces growth

Question 318

What happens as a result of tyrosine kinase receptor activation?

Answer 318

Transcriptional effects - changes in gene expression etc Changes in protein activity - could change properties of cell

Question 319

Why so downstream signals activated by RTKs and GPCRs overlap?

Answer 319

So they can end up in target proteins that are turned on Or can induce transcriptional changes / regulation

Question 320

Why do cells normally have a combination of G protein coupled receptors GPCRs and receptor tyrosine kinases RTKs?

Answer 320

So that Ligands binding to receptors can converge

Question 321

What are the 4 basic mechanisms for cellular communication?

Answer 321

Contact dependant (direct contact) Paracrine signalling Synaptic signalling Endocrine signalling

Question 322

What is contact dependant signalling?

Answer 322

Where 1 cell has a protein, glycoprotein or glycolipid on surface that is going to act as a ligand for receptor on cell next to it! Need to be physically next to eachother to send that signal

Question 323

What is paracrine signalling?

Answer 323

Send messages to cells immediately near them - short lived signals

Question 324

What is synaptic signalling?

Answer 324

From nerve to target cell Neurotransmitters in axon, are already packaged in synaptic cleft, ready to be released When released > very small diffusion distance, can respond quickly!

Question 325

What is endocrine signalling?

Answer 325

Signals designed to travel furthest, go in blood to other sites in body Act wherever the target cell has got a corresponding receptor

Question 326

Why is cell communication / signalling so important?

Answer 326

Regulates cell behaviour - depends on multiple extracellular signal molecules Allows cells to: survive, grow and divide (proliferate) and differentiate (more specialised cells eg monocytes

Question 327

What would happen to a cell if there was NO stimulus / cell communication?

Answer 327

Cell would die! Apoptotic cell

Question 328

What is KEY about contact dependant signalling?

Answer 328

Cell can’t exist / survive unless they have contact dependant communication from cells around them

Question 329

What type of cells don’t need contact dependant signalling?

Answer 329

Blood cells - leukocytes, erythrocytes As they are in suspension

Question 330

What are examples of paracrine signalling?

Answer 330

Fibroblast growth factor FGF - proliferation and differentiation Transforming growth factor beta TGFB Wnt signalling - embryo development Chemotaxis

Question 331

What is chemotaxis? (Paracrine signalling)

Answer 331

Motility in the direction of a localised mediator Bacterial toxins - formyl peptides Chemokines - ILB

Question 332

Why do phagocytes follow around bacteria and engulf it?

Answer 332

Because chemokines are being released The higher the concentration of them, the easier it is for leukocyte or phagocyte to follow it

Question 333

What are the steps of Cholinergic transmission?

Answer 333

1. Synthesis of acetylcholine 2. Uptake into storage vesicles 3. Release of neurotransmitter 4. Binding to receptor 5. Degradation of acetylcholine 6. Recycling of choline

Question 334

Why is endocrine signalling different to the others?

Answer 334

Longer lasting signals because they need to travel far or need to be constantly in contact with cell next to them Taken everywhere by the blood ONLY works if you have receptor and the signal

Question 335

Extracellular signals can act slowly or rapidly. Examples of these?

Answer 335

Slowly - growth, cell division, transcription Rapidly - cell movement

Question 336

Different cell types respond differently to the … extracellular signal molecule Eg acetylcholine

Answer 336

Same

Question 337

How is calcium signalling detected?

Answer 337

Fura 2 am An aminopolycarboxylic acid which binds to free calcium It is a ratiometric fluorescent dye - changes intensity of signal with calcium concentration It is excited at 340nm and 380nm light Ratio of emissions at those wavelengths is directly related to the amount of intracellular calcium Ie. If there’s a high concentration of calcium = high signal intensity and vice versa

Question 338

What are the common disaccharides that are linked by glycosidic bonds? (Composed of 2 monosaccharides)

Answer 338

Sucrose - glucose and fructose Lactose - galactose and glucose Maltose - glucose and glucose

Question 339

Why do dietary carbohydrates have to be broken into monosaccharides in humans?

Answer 339

We have transporters specific to monosaccharides. So have to be broken down to facilitate entry into the small intestine

Question 340

What is sucrose intolerance due to?

Answer 340

Sucrase enzyme deficiency High in Icelandic population

Question 341

What is lactose intolerance due to?

Answer 341

Lactase enzyme deficiency - most common!

Question 342

What is sorbitol intolerance due to?

Answer 342

Sorbitol dehydrogenase enzyme deficiency - converts sorbitol into fructose which can then enter glycolysis Sorbitol found in pears, avocados and is used as a low calorie sweetener Sorbitol is metabolised very slowly by most humans

Question 343

What are homopolysaccharides and what are some examples?

Answer 343

Consist of 1 type of monosaccharide Best examples are glycogen, Starch - both homopolysaccharides consisting of glucose

Question 344

What are heteropolysaccharides and some examples?

Answer 344

Contain different types of sugars / quite often linked to proteins (glycoproteins) and the glycoproteins are important in viral infections etc

Question 345

What is glycogen?

Answer 345

Major storage form of glucose in humans and other animals

Question 346

How much glycogen can the liver store?

Answer 346

200g

Question 347

What enzymes are required to break the bonds in glycogen?

Answer 347

A1-4 : glycogen phosphorylase A1-6 : debranching enzyme

Question 348

What 2 organs store glycogen?

Answer 348

Liver - to provide glucose in fasting phase 6-8hrs after last meal. To prevent hypoglycaemia Skeletal muscle - can store up to 300g glycogen depending on exercise level

Question 349

What is the difference between skeletal muscle and liver glycogen?

Answer 349

In skeletal muscle, glycogen has to be utilised during exercise to make ATP Skeletal muscle DOES NOT have glucose transporter to transport glucose out!

Question 350

Glycogen

Answer 350

Branched homopolysaccharide of glucose Glucose monomers form a1-4 linked chains Branch points with a1-6 linkers every 8-12 residues Molecular weight reaches several millions MAIN storage polysaccharide in a animals

Question 351

Starch

Answer 351

A mixture of 2 homopolysaccharides of glucose: Amylose - unbranded, a1-4 Amylopectin - branched, a1-6 every 24-30 residues Starch is the main storage polysaccharide in plants

Question 352

Cellulose

Answer 352

Most common polysaccharide in the world! B1-4 glucose units Hydrogen bonding between chains Water insoluble Cellulases: bacteria in ruminants and termites

Question 353

Why can humans NOT digest cellulose?

Answer 353

1. Cellulose contains B1-4 bonds and we do not have the enzymes (cellulases) required to break them down 2. Hydrogen bonding means cellulose is water insoluble and we need things to be water soluble to digest them

Question 354

How is energy generated when two pyruvates are produced per glucose?

Answer 354

By reducing NAD+ to NADH By phosphorylation of ADP to ATP

Question 355

What is the net yield of NADH and ATP from 1 glucose?

Answer 355

2NADH 2ATP

Question 356

When does anaerobic metabolism take place?

Answer 356

Takes place in conditions of oxygen deficiency

Question 357

Why do we get the conversion of glucose > pyruvate > lactate?

Answer 357

Due to inhibition of oxidative phosphorylation due to LACK of oxygen This inhibits krebs > inhibits conversion of pyruvate to Acetyl CoA

Question 358

Under what conditions does lactate production take place?

Answer 358

Oxygen depletion - eg when you train Hypoxia - lactate used as a bio marker for how much hypoxia there is Red blood cells - don’t have mitochondria Warburg effect - cancer cells / tumours use anaerobic metabolism as they have low level of oxygen transport

Question 359

Cows have bacteria in their forgut that secrete cellulases What do these do and how are they metabolised?

Answer 359

Cellulases break down cellulose to glucose Glucose 1st metabolised by the bacteria to pyruvate. In the anaerobic environment of the forgut, pyruvate is converted into volatile fatty acids!

Question 360

Cows DONT take up glucose, they take up…

Answer 360

Volatile fatty acids

Question 361

What are the volatile fatty acids?

Answer 361

Acetate - 2C Propionate - 3C Butyrate - 4C

Question 362

How is acetate utilised by the cow?

Answer 362

Feeds into Krebs cycle as a 2 carbon donor - forms Acetyl CoA

Question 363

How is butyrate utilised by the cow?

Answer 363

Forms a B- hydroxybutyrate which is a ketone body and can be broken down into Acetyl CoA Used as an energy source

Question 364

How is propionate utilised by the cow?

Answer 364

Converted into lactate in the liver Lactate > pyruvate and pyruvate > glucose via gluconeogeneis

Question 365

When cows eat grass, the bacteria produce the glucose but the cows DO NOT take up the glucose, they take up … to then make the glucose! Cows get the glucose from… Disadvantage?

Answer 365

Volatile fatty acids Gluconeogenesis

Question 366

What is a Uniport glucose transporter?

Answer 366

Transports 1 compound across the membrane and is driven by diffusion - high to low concentration

Question 367

What is a Symport cotransporter?

Answer 367

Transports 2 compounds across membrane

Question 368

What is an Antiport cotransporter?

Answer 368

Transports 1 compound into the cell and another out of the cell!

Question 369

Uniport transporter amino acid is in the membrane. What are its 2 confirmations? Eg GLUT1 - erythrocytes

Answer 369

T1 - confirmation that opens to outside and will bind glucose T2 - conformation that opens to other side of membrane

Question 370

How do the Uniport Energy Independent Transporters work?

Answer 370

Binding glucose causes a conformational change that converts T1 into T2. T1 had a high affinity for glucose T2 has a low affinity for glucose so releases it into the cell! This changes conformation back to T1, opening up outside of cell and allowing another glucose to bind

Question 371

GLUT = glucose transporter What type of transporters are GLUT 1,3,4 and 5?

Answer 371

High affinity glucose transporters, so bind glucose at very low concentrations So can transport glucose even under fasting conditions! Are uni - directional: only transport glucose in 1 direction

Question 372

The different GLUT transporters

Answer 372

GLUT1: erythrocytes and brain GLUT2: liver, kidney, intestine, pancreatic B cells (bi directional) GLUT3: neurons GLUT4: adipose tissue, skeletal muscle (the ONLY one regulated by insulin and glycogen) GLUT5: small intestine, testes, muscle GLUT6: gluconeogenic tissues

Question 373

What is special about GLUT5?

Answer 373

Specific / has a high affinity for fructose, found in small intestine Fructose intolerance linked to low expression of GLUT5 in small intestine

Question 374

What is special about GLUT7?

Answer 374

Only expressed in ER! Specifically required during gluconeogenesis

Question 375

What is special about GLUT 1,3 and 4?

Answer 375

Glucose uptake form blood (high affinity)

Question 376

What is special about GLUT2?

Answer 376

Bi directional (low affinity)

Question 377

GLUT 4 in fasting conditions is stored in vesicles inside the cell. Insulin is secreted in healthy individuals when blood glucose concentrations are ABOVE 6MM. What does binding of insulin trigger?

Answer 377

Triggers a set of enzymes (signalling cascade) to initiate phosphorylation or de phosphorylation actions This leads to transfer of GLUT4 vesicles to plasma membrane Vesicles fuse with membrane and GLUT4 transporters are expressed on membrane = biologically active! When glucose concentrations are reduced, there’s a reduction of Insulin and inactivation of this cascade

Question 378

What are some potential negative effects of glucose in the blood?

Answer 378

Glycation of proteins - means theres a NON enzymatic modification of proteins in the blood Eg glycated haemoglobin transports LESS oxygen and is used as a bio marker For long term high blood glucose Proteins in the eyes can get glycated - can lead to blindness!

Question 379

How is adipose tissue important for metabolism?

Answer 379

Adipose tissue is there to store energy Glucose is transported into the tissue where it is stored in the form of triglycerides!

Question 380

Sodium dependant monosaccharide co transport system

Answer 380

Transports glucose AGAINST concentration gradient Energy requiring process: Chemical + electrical potential / Na+K+ ATPase Co transport of Na+ Epithelial cells of intestine, renal tubules

Question 381

What is the Kt / Kd?

Answer 381

The dissociation constant The lower the kt, the higher the affinity for that ligand!!

Question 382

What does the initial velocity of glucose mean?

Answer 382

The rate at which glucose is transported into the cell!

Question 383

What is a function of epithelial cells?

Answer 383

To transport dietary carbohydrates into the blood

Question 384

How does glucose get from intestinal lumen into epithelial cells?

Answer 384

Using a Symport protein - a sodium DEPENDANT co transporter The sodium provides the energy to transport glucose against CG Can do this because concen of sodium outside cell in intestinal lumen is HIGHER than inside And sodium is + charged whereas inside of the cell is - charged

Question 385

How does glucose get out of the cell into the blood?

Answer 385

Using a GLUT 2 transporter as it is bi directional It is expressed on the basal surface It transports glucose out of the cell when there’s HIGH concentrations inside

Question 386

Intestinal lumen: Na+ glucose Symporter on apical surface is driven by…

Answer 386

High extracellular na+ concentration

Question 387

Blood: Glucose uniporter GLUT2 on basal surface facilitates…

Answer 387

Downhill efflux of glucose

Question 388

What does the sodium potassium ATPase Antiport protein do? Inside and outside of the cell?

Answer 388

It transports Na+ out of the cell to help maintain low sodium concentration Inside cell: maintains - charge inside cell and can drive glucose uptake through Na+ glucose symporter K+ is also driven into the cell at the same time!

Question 389

What does guanylyl Cyclase do?

Answer 389

Converts GTP into cyclic GMP - cGMP

Question 390

How is guanylyl Cyclase different to adenyl Cyclase?

Answer 390

Receptor associated (not membrane associated) Soluble - can be activated by things like nitric oxide

Question 391

What do all the mechanisms of decreases signalling do?

Answer 391

They ALL decrease the output from the signalling pathway!

Question 392

What is receptor sequestration?

Answer 392

Receptor associated with signal and get internalised in an Endosome Ph drops + ligand is released from receptor - ligand then degraded by proteins in endosome Receptor will get recycled back out to membrane ^ in endocytosis will decrease amount of receptors on cell surface

Question 393

What is receptor down regulation?

Answer 393

Further drop in ph and endosome becomes LATE endosome + then lysosome by fusion! Degrades ALL components and receptor NOT allowed back onto cell surface Permanently reduces no of receptors on cell surface. Less receptors = less response

Question 394

What is receptor in activation?

Answer 394

While receptor bound to ligand, it causes some intra cellular processes that cause inhibition May modify receptor - stops it receiving signals Or methylation or acetylation may cover phosphorylation site = stops proteins associating with receptor when activists = self limiting!

Question 395

What is inactivating of signalling protein?

Answer 395

Inhibition may inactivate the down stream enzyme = inactivation of signalling proteins

Question 396

What is production of inhibitory protein?

Answer 396

When there’s activation of enzymes with enzyme associated receptors, we get an inhibitory process A protein can inhibit activation of receptor Does this through physical binding

Question 397

What are the mechanisms of decreased signalling?

Answer 397

Receptor sequestration Receptor down regulation Receptor inactivation Inactivation of signalling protein Production of inhibitory protein

Question 398

What is the role of B arrestin in GPCR desensitisation?

Answer 398

B arrestin binds to phosphorylated GPCR Which prevents the re association of the trimeric G protein (GRK) with receptor = preventing further signals! Only works if there are multiple phosphorylation sites (hyper phosphorylation)

Question 399

B arrestin prevents further signalling in GPCR. So can’t activate downstream things like:

Answer 399

Adenyl Cyclase Can’t generate IP3 Can’t release calcium Can’t produce diasolglycerol

Question 400

What can scaffolding proteins do?

Answer 400

Control the signalling cascade

Question 401

Scaffold protein 1 has a very specific binding / docking site for kinase A,B and C Why is it essential?

Answer 401

Only lets them sit in that order! They have to bind in that order to receive the signal = specific response

Question 402

What does docking / scaffolding ensure?

Answer 402

Ensures that everything is kept close together in the membrane for rapid transmission of the signal!

Question 403

Sev RTK activates Ras in the fly eye What is the equivalent of the adapter protein Drk in humans?

Answer 403

Grb2 and Ras GEF (also called seven less SOS)

Question 404

How does the Sev RTK in fly eye bind? How is it similar to humans?

Answer 404

The adaptor protein (Drk) binds through SH3 and SH2 domains to the Ras GEF (SOS) - same as humans! As it is a guanine exchange factor it swaps out GDP and inactive Ras binds instead to GTP! Can only do that in the presence of GEF. Now it is active > shape change > downstream signalling

Question 405

What is the difference between Drk in fly eye and humans?

Answer 405

IGF1 is binding to soluble peptides that are travelling around the body Here, we’ve got Contact Dependent Signalling as a result of engagement of 2 membrane bound components

Question 406

What do the interaction domains - Src homology - do?

Answer 406

Src homology domains bind to phosphotyrosine residues in tyrosine kinases - acting as a scaffold to recruit further signalling components

Question 407

Proteins have lots of domains - what are they?

Answer 407

Patterns of amino acids that make a particular shape and allow something to bind to it Complementary to a particular protein

Question 408

Jack of all trades has … interaction domains

Answer 408

Many

Question 409

What is an interaction domain?

Answer 409

Means there is a platform for a protein to interact with another protein

Question 410

Ras family GTPases activate a MAP kinase signalling molecule:

Answer 410

MAP kinase kinase kinase - Raf is important in cell proliferation and induces a phosphorylation cascade 1 molecule of Ras may be enough to phosphorylate thousands of the MAP kinase kinase - Mek! The cascade exponentially ^ the number of the final output Map kinase - Erk, which can cause 2 effects

Question 411

What are the 2 effects that MAP kinase - Erk can induce?

Answer 411

Changes in protein activity - eg protein kinase A can phosphorylate something in the nucleus Takes seconds or minutes Changes in gene expression - takes hours or days = SLOW

Question 412

What does the PI 3 / PKB (Akt) signalling pathway stimulate? What is Akt activated by?

Answer 412

Animal cells to survive and grow By mTOR in complex 2 with rictor

Question 413

What happens if we get dissociation of Akt from its complex?

Answer 413

It can associate with mTOR in a separate complex - complex 1. This can induce cell growth If it stays there - it is able to phosphorylate Bad - a protein that sits in mitochondrial membrane

Question 414

What happens to the Bad protein if Akt is present?

Answer 414

Akt will act as a kinase and phosphorylate Bad. This inactivates it and it binds to a 14 3 3 protein = signal for degradation! (Ubiquitin ligase signal) Also get release of an active form = induces inhibition of apoptosis = sign for cell survival! (When Akt is NOT present, Bad is associated with its inhibitory complex)

Question 415

What is mTOR and what protein complex is it in?

Answer 415

mTOR = mammalian target of rapamycin Either in protein complex 1 or 2, NOT both!

Question 416

What does mTOR in complex 2 contain?

Answer 416

Rictor protein Insensitive to rapamycin, activates Akt / PKB

Question 417

What does mTOR in complex 1 contain?

Answer 417

Riptor protein Sensitive to rapamycin Promotes ribosome production and protein synthesis and inhibits protein degradation Complex 1 stimulates cell growth and survival through nutrient uptake and metabolism

Question 418

What happens when mTOR in complex 1 DOES NOT have growth factor?

Answer 418

Active Tsc2 > inactive Rheb > inactive mTOR = NO CELL GROWTH

Question 419

What happens to mTOR in complex 1 when it has growth factor present?

Answer 419

Active PI 3 kinase > active Akt > active Tsc2 > active Rheb > active mTOR= Cell growth!

Question 420

What is the role of JAK in regards to cytokines?

Answer 420

When a Cytokine binds to its receptor and JAK is there - you get cross phosphorylation and a dimer forms It activates the kinase associated with the receptor!

Question 421

What is the role of STAT in regards to cytokines?

Answer 421

Forms a dimer - only if phosphorylated by JAK Dimer form =‘effective nucleur localisation signal = can pass through nucleur pore complex and associate with specific sequence Associate with GTFs > forms mediator complex > turns ON gene transcription Eg - BCL2 containing proteins that either induce or protect from apoptosis

Question 422

Phosphorylated tyrosines on RTKs serve as … for intracellular signalling proteins

Answer 422

Docking sites

Question 423

What is a mutant tyrosine kinase domain?

Answer 423

Means that despite getting the signal and the 2 molecules coming together, it CAN’T become activated! Means there no phosphorylation and no docking sites are generated

Question 424

How do mutant tyrosine domains work in a dominant negative manner? How is this problematic?

Answer 424

One copy stops the receptor from being activated at all, so cannot pass on ANY signal from this receptor! Problematic: failure to induce proliferation to fight off infections etc Problematic: receptor could be constantly turned on > induces lots of proliferation > could generate cancer etc

Question 425

What is cholesterol?

Answer 425

A versatile molecule with a rigid steroid ring structure, a tail and a hydroxyl group

Question 426

What does uptake of all lipids from the diet require?

Answer 426

Requires emulsification (which needs bile acids) and formation of chylomicrons for transport to the liver for processing

Question 427

What is the effect to the liver of bile acids that are NOT bound to lipid droplets?

Answer 427

Can be toxic to the liver Their binding to nuclear hormone receptors enables them to increase expression of enzymes that will degrade them through a transcriptional mechanism

Question 428

What do lipoproteins generated by the liver do?

Answer 428

Enable transport of lipids around the body to tissues where it can be stored or used. They use the amphipathic nature of some lipids to envelop those without this property

Question 429

What does the contents of outside the lipoproteins dictate?

Answer 429

Where the particles are destined for

Question 430

Why are interactions between the components of the cell membrane essential?

Answer 430

Essential to maintain its integrity and prevent the cell from dying

Question 431

What are the components of the cell membrane?

Answer 431

Phospholipids - polar head and long fatty acid tails Cholesterol - important for maintaining fluidity of membrane Protein Glycoprotein Glycolipid

Question 432

Components of the cell membrane are amphipathic What does this mean?

Answer 432

Both lipid loving and water loving > lipophilic and hydrophilic

Question 433

What do unsaturated fatty acids contain?

Answer 433

A 30 degree kink - means other FA can’t be next to it > means solution is more fluid!

Question 434

Why are phos. Serine and phos. Amine on the INSIDE of the membrane? What’s on the outside of the lipid bilayer?

Answer 434

They are negatively charged! There’s an overall electron negative charge on inside of membrane Phos.choline and sphingomylein are on outside

Question 435

Some cells have more cholesterol than others. Why do erythrocytes have a ratio of phospholipids: cholesterol of 1:1?

Answer 435

Need to have a concave shape > so need to be good at maintaining shape > strong, resilient So needs a LESS fluid membrane than hepatocytes of liver etc

Question 436

Properties of cholesterol (sterol)?

Answer 436

4 ring ridged structure at the centre - makes molecule inflexible! Saturated hydrocarbon tail - Van der Waals forces with phospholipids around it

Question 437

Cholesterol is used to generate Bile acids Why is this important?

Answer 437

Important in digestion > in encouraging the breakdown of lipids

Question 438

What is the rate limiting step in production of cholesterol? What happens is there’s a single base change ( a variant) in HMG reductase?

Answer 438

HMG CoA reductase - controls how quickly cholesterol is generated and therefore things like steroid hormones, fat soluble vitamins and bile acids HMG reductase will work faster than normal! Generates excess amount of cholesterol > eg in people that have hypocholesterolaemia

Question 439

Properties of bile acids / salts?

Answer 439

Synthesised from cholesterol Essential for lipid digestion Increase solubility Increase surface area - increase rate of reaction + rate of digestion

Question 440

Primary bile acids are quite reactive and very toxic so are converted to to less reactive and less toxic secondary bile acids. What is the effect of this conversion / conjugation? What problems could highly toxic primary bile acids cause in the liver?

Answer 440

Additions / conjugation increases solubility > need things to be hydrophilic to get rid of them from body Could cause Colistasis in the liver - bile build up

Question 441

Myocyte? Adipocyte?

Answer 441

Cardiac cells > need lots of energy Storage

Question 442

The gallbladder stores bile ready for release. How does it do this?

Answer 442

First it concentrates it for storage and then dilutes it in response to fats detected in the small intestine through release of cholecystokinin CKK

Question 443

Bile acids can be modified by conjugation. What is this? It makes the original product…

Answer 443

The formation of a link between an amino acid with a waste or toxic product Less toxic More hydrophilic + soluble Easier to excrete

Question 444

What is the effect of cholesterol + saturated fatty acid tails?

Answer 444

It will make the phospholipid bilayer more rigid = stiffening effect

Question 445

What happens in bilayers where there are lots of UN- saturated fatty acid tails in phospholipids?

Answer 445

Cholesterol will make the bilayer more fluid

Question 446

What are the main ways for phospholipids to be dynamic in the membrane?

Answer 446

Lateral diffusion, flexion, rotation - occur without enzyme activity > most frequent Flip flop - rarely occurs unless it is enabled by an enzyme / channel

Question 447

Saturated FA tails + phospholipids =

Answer 447

Thicker membrane > more stability > rigid

Question 448

Un saturated FA tails + phospholipids =

Answer 448

Slightly thinner membrane > less stable > more fluid

Question 449

Why is there lots of phos. Choline in the liver?

Answer 449

There’s a large surface area there > hepatocytes have lots of exchange > so need fluid membranes to have fast transport over membrane

Question 450

Why is phos. Serine relatively low in all cells and organelles?

Answer 450

As it is negatively charged on inside of membrane > maintains electrostatic interaction May appear on the outside of membrane if platelets are activated

Question 451

Why does Myelin have lots of phos. Ethanolamine and cholesterol?

Answer 451

It insulates nerves and allows Saltatory conduction > needs to be thick

Question 452

Why do mitochondria and ER have different ratios of lipid components?

Answer 452

Cholesterol increases as move out towards cell membrane > mitochondria doesn’t have much > doesn’t need to be rigid, just needs to form barrier RER needs to be more rigid as ribosomes will be making proteins and transporting

Question 453

What are lipid rafts?

Answer 453

Collections of lipids brought together by cholesterol

Question 454

Properties of lipid rafts? When are they used?

Answer 454

Acts as an anchor for proteins Prevent movement of membrane components around ‘fluid mosaic’ membrane > reducing movement and diffusion Require location specific functions - eg receptors need to be in synapse Contain specific protein subunits - eg associate in membrane to be activated Makes sure membrane components are physically close to interact - otherwise won’t be functional!

Question 455

What is cell polarity? (Affects lateral diffusion)

Answer 455

Essential that the cell knows where up/down and inside / outside is Needs to be some kind of barrier to stop too much diffusion otherwise they will mix up areas of the membrane > eg Tight Junctions - rigid structures that are a big obstacle to any movement

Question 456

Confocal microscope

Answer 456

Can start to focus at lots of different places throughout the cell! Can see whole of the cell in little segments Can make a 3D rendition

Question 457

What’s happens to propidium iodide (lipophilic dye) when it moves into cell and the cell is alive? When the cell is struggling to survive?

Answer 457

Alive - immediately kicked out by ATPases Struggling to survive - prop iodide can’t exit cell > flipase and flopase are turned off so can’t get rid of it > cell death!

Question 458

Annexin V (binds phospatidylserine) only has access to the outside of membrane > can’t move across as it is NOT lipophilic What does it show in early vs late apoptosis?

Answer 458

Early - still some phos. Serine on the outside > Sramblase turned on > still some ATP as low concentration of prop iodide > flipase and flopase control levels Late - large volumes of prop iodide and phos. Serine (lots of dye stained) > BAD > ATP no longer abundant > cells definitely going to die > phos. Serine in the outside and prop Iodide NOT kicked out!

Question 459

Modification changes enable the activation of enzymatic function or recognition by another protein. Methods include:

Answer 459

Phosphorylation - negative charge changes properties of + charged AA Acetylation - prevents other things activating protein Methylation - same as acetylation Cleavage - cutting longer AA sequence into shorter one to = activated protein

Question 460

Protein … and … are employed in virtually all signalling pathways

Answer 460

Kinases Phosphatases

Question 461

What is the process of a simple signalling cascade? (1 kinase and 1 target protein)

Answer 461

Ligand will only bind receptor if BOTH parts of binding sites are present When it binds ligand there is shake change in receptor Kinase domains are now closer together =ACTIVE. Are able to start phosphorylating things It can phosphorylate a protein > changes the proteins shape > can dimerise with 1 other protein Go into nucleus as proteins have nuclear localisation signal > can activate gene expression > bind DNA > stimulate transcription Nuclear phosphatase in nucleus will de phosphorylate proteins = INACTIVE Moves out into cytoplasm to repeat process

Question 462

What are the 3 methods to ensure transmission of a signal?

Answer 462

Scaffolding Docking sites Complex formation

Question 463

The domino effect amplifies extracellular signals - what does it enable?

Answer 463

Activation of multiple pathways to induce multiple effects simultaneously Convergence of multiple pathways on a single target

Question 464

Ion channel receptors

Answer 464

Form a pore in membrane Only open when it’s signal particle is bound to protein Restrict movement of ions from one side of membrane to another

Question 465

G protein receptors

Answer 465

7 transmembrane domain containing proteins embedded in membrane 4 flavours

Question 466

Enzyme coupled receptors

Answer 466

Single pass transmembrane receptors that ‘dimerise’ in membrane in response to ligand binding Activate eachother to recruit intracellular proteins Often result in use of secondary messengers

Question 467

Ion channel receptor examples

Answer 467

Nicotinic Acetyl choline receptors - cation channels, mostly K+ and Na+ GABA receptors - inhibitory NT (nerve terminus), chloride channel, hyper polarises cell

Question 468

What do trimeric G proteins do?

Answer 468

Relay signals from GPCRs

Question 469

How are G proteins activated by activated GPCRs?

Answer 469

Binding of ligand to GPRC leads to displacement of GDP from the inactive trimeric G protein complex Binding of GTP to the trimeric G protein leads to its activation and dissociation into a, b and y subunits

Question 470

What does phospholipase C metabolise?

Answer 470

Phosphorylated lipids such as PIP2 PIP2 is needed for adaptor proteins to bind so we can get Clathrin binding Needed for things that associate with Dynamin

Question 471

What is PIP2 hydrolysed into?

Answer 471

IP3 - releases Ca2+ from the ER DAG - activates protein kinase C

Question 472

How are adenylyl Cyclase, cAMP and protein kinase A (PKA) related?

Answer 472

When low levels of cAMP are present, protein kinase A is inactivated by binding of regulatory subunit When adenyl Cyclase activated and produces cAMP, [cAMP] increases PKA has greater affinity for cAMP than the regulatory subunit so cAMP binding then releases inhibitory subunit and PKA becomes active! Activated PKA can move into nucleus and phosphorylate CREB etc which controls transcriptional activation of gene promoters

Question 473

What are receptor tyrosine kinases?

Answer 473

Directly phosphorylate specific tyrosine residues on receptor itself and on other intracellular proteins

Question 474

When a protein , amino acid or peptide ligand binds to its receptor a …

Answer 474

Second messenger molecule is activated

Question 475

G proteins are active when …

Answer 475

GTP is bound

Question 476

What uses local signalling methods?

Answer 476

Neurotransmitters

Question 477

A hormone released from a cell into the blood is found in what type of signalling?

Answer 477

Endocrine

Question 478

Water soluble hormones act on…

Answer 478

Cell surface receptors

Question 479

Hormones cause multiple responses by…

Answer 479

Using multiple receptors Causing different cellular responses

Question 480

Hormone pairs with opposite effects are called…

Answer 480

Antagonistic pairs

Question 481

Ligand gated ion channels are specific for …

Answer 481

The ligand and the ion type

Question 482

Synaptic signalling involves …

Answer 482

Releasing hormones form a neuron

Question 483

Steroid hormones are located…

Answer 483

Inside the cell

Question 484

Membrane is synthesised in the …

Answer 484

SER

Question 485

New membrane is …

Answer 485

Symmetrical

Question 486

Vesicles are used to transport new membrane to the Golgi What do they use as a coat protein?

Answer 486

COP2

Question 487

Membrane moving OUT to the plasma membrane uses what as a coat protein?

Answer 487

Clathrin

Question 488

The PLASMA membrane is…

Answer 488

Asymmetrical

Question 489

In the OUTER leaflet you find…

Answer 489

Phos. Choline and Sphingomyelin

Question 490

In the inner leaflet you find…

Answer 490

Phos. Serine and phos. Ethanolamine

Question 491

Scramblase is a protein that moves phospholipids between layers. What ion is it dependant on?

Answer 491

Ca2+

Question 492

During activation of Apoptosis, phospholipids move in the membrane because …

Answer 492

Calcium release activated scramblase action

Question 493

Anaerobic metabolism of glucose is important under the following conditions / situations?

Answer 493

Anaerobic bacteria Exercising muscle (oxygen limitation) Ethanol metabolism (yeast) Hypoxia (humna eg heart attack) Some cancers

Question 494

What tissues can store glycogen?

Answer 494

Liver - up to 200g Skeletal muscle - up to 300g

Question 495

The erythrocytes produce lactate. Why?

Answer 495

The LACK mitochondria, therefore cannot undertake aerobic glycolysis

Question 496

Forgut metabolisers eg cows have bacteria in the foregut that metabolise cellulose and glucose. What is the main disadvantage for the cow?

Answer 496

The cows have to convert the volatile fatty acids (products of bacterial glucose metabolism) into glucose via gluconeogenesis

Question 497

Foregut metabolisers eg cows have bacteria in the forgut that convert glucose into volatile fatty acids. What are the potential advantages?

Answer 497

The cows forgut contains bacteria that secrete Cellulase The bacteria produce vitamins and amino acids that the cow can utilise The bacteria remove toxins

Question 498

Glycolysis: what phase A) provides 2 net ATP molecules B) utilises 2 ATP molecules C) provides 4 ATP molecules

Answer 498

A) the overall pathway B) the preparatory phase C) the pay off phase

Question 499

The enzyme pyruvate kinase is INHIBITED by Acetyl CoA. What is Acetyl CoA a product of?

Answer 499

Fatty acid beta oxidation pathway

Question 500

The metabolic fate of pyruvate can include the following DIRECT products:

Answer 500

Lactate under anaerobic conditions Lactate under hypoxia conditions Volatile fatty acids by bacteria in the rumen of cows Oxaloacetate under gluconeogenic conditions Ethanol in yeast under anaerobic conditions Acetyl CoA under aerobic respiration conditions

Question 501

Identify the glucose sparing pathways

Answer 501

Glucose alanine cycle Cori cycle

Question 502

The Hexokinase enzyme utilises ATP as a co substrate. Identify the functions of ATP in this reaction:

Answer 502

Donates an inorganic phosphate Pi Hydrolysis of ATP to ADP provides energy to drive the reaction from glucose to glucose 6 phosphate

Question 503

The Hexokinase enzymes utilise Mg2+ as a co substrate. Identify the functions of Mg2+ in this reaction

Answer 503

It helps correctly orientate the substrates It helps to reduce electrostatic charge, thus electrostatic repulsion

Question 504

In anaerobic glycolysis (lactate production), no NADH is produced. Why?

Answer 504

NADH is produced in the conversion of glucose to pyruvate But NADH is utilised in the conversion of pyruvate to lactate

Question 505

What characteristics apply to Hexokinase 1?

Answer 505

Ubiquitous expression Broad specificity for hexose monosaccharides Product inhibition Hyperbolic kinetics Low km and vmax for glucose Catalyses an irreversible reaction - ie uni directional Is a control point in glycolysis!

Question 506

Identify metabolic indicators of high energy status in the cell

Answer 506

ATP Citrate - utilised in TCA cycle

Question 507

Conversion of fructose 6 phosphate to fructose 2,6 bisphosphate is catalysed by what enzyme?

Answer 507

Phosphofructokinase 2 - PFK2

Question 508

Allosteric compounds can be identified by…

Answer 508

Sigmoidal kinetics

Question 509

Identify the enzyme products that are controlled directly by the insulin / glucagon ratio

Answer 509

Fructose 2,6 bisphosphate Pyruvate

Question 510

What ONLY applies to liver pyruvate kinase? L PK

Answer 510

Activation by insulin action

Question 511

The 2nd most common form of enzyme linked haemolytic anaemia is caused by deficiency in the … enzyme

Answer 511

Pyruvate kinase

Question 512

What metabolites are NOT substrates for gluconeogenesis in humans?

Answer 512

Long chain fatty acids Acetyl CoA

Question 513

In glycolysis there are 3 uni directional (irreversible) enzyme catalysed reactions that are bypassed by … in gluconeogenesis

Answer 513

4

Question 514

What proteins and enzymes are involved in the hydrolysis of glucose 6 phosphate to glucose, and the transport of the latter out of the cell?

Answer 514

Glucose 6 phosphate Glucose 6 phosphate transporter GLUT 2 GLUT 7

Question 515

Pyruvate is a substrate for gluconeogensis. During this is is NOT derived from…

Answer 515

Glucose Beta oxidation of fatty acids

Question 516

What statement relating to pentose phosphate pathway is NOT correct?

Answer 516

The ppp provides NADPH for energy production

Question 517

The primary point of regulation in the pentose phosphate pathway is…

Answer 517

The glucose 6 phosphate dehydrogenase enzyme

Question 518

What intermediate in the pentose phosphate pathway is utilised for the synthesis of aromatic amino acids?

Answer 518

Erythrose 4 phosphate

Question 519

What molecule is a free radical?

Answer 519

O2 -

Question 520

What are the protective mechanisms against oxidative stress?

Answer 520

Glutathione peroxidase Superoxide dismutase SOD Vitamin C Vitamin E

Question 521

GSH reduced glutathione is oxidised to GSSG oxidised glutathione by…

Answer 521

Glutathione peroxidase

Question 522

The cytochromes P450 are …

Answer 522

Phase 1 drug metabolising enzymes

Question 523

Glucose 6 phosphate dehydrogenase deficiency…

Answer 523

Is linked to haemolytic anaemia Provides resistance to malaria Is the most common form of enzyme linked haemolytic anaemia Causes neonatal jaundice

Question 524

What are the 8 mechanisms of membrane insertion?

Answer 524

Single pass proteins Multi pass proteins Channel Not membrane spanning but embedded in the membrane Lipid anchored Glycolipid anchored Adaptor proteins Accessory proteins

Question 525

What are lipid anchors?

Answer 525

Rely on interactions between FA chain and phospholipid tails Raft formation ensures proximity to transmembrane proteins All have LONG CHAIN fatty acid tails > easily integrates into membrane next to FA tails of phospholipids > longer they are, better the anchor > more van der waals forces

Question 526

Myristoyl anchor

Answer 526

Large number of carbons Amide linkage > attaches lipid to N terminus (NH group)

Question 527

Palmitoyl anchor

Answer 527

Attached by a thioester linkage to sulphur group (present on cysteine AA) Benefit: can be anywhere! N or C terminus, OR in the middle > versatile

Question 528

Farmesyl anchor

Answer 528

Thioester linkage to C terminus C=O group Unsaturated FA > fits in better than saturated

Question 529

How are proteins inserted into the membrane?

Answer 529

Polypeptide chain needs to form cylindrical structure allowing charged / polar AA to be hidden from hydrophobic middle of the bilayer > otherwise helix can’t be embedded in membrane Uncharged / NON polar AA on outside of cylinder enable interaction with fatty acid tails ER will check that all hydrophobic AA are on outside and hydrophilic on inside!

Question 530

What is the Hydropathy Index?

Answer 530

The measure of how hydrophobic (or not) something is! The further up on the scale > the MORE hydrophobic it is and the further down > the least hydrophobic it is! Below the line on the index > in the cytoplasm OR outside of the cell > aqueous environment > very hydrophilic

Question 531

What is the function of a selectivity filter?

Answer 531

Charges and polarity in the centre of the pore in the channel makes it selective for its ligand!

Question 532

What gives membranes strength?

Answer 532

Spectrin heterodimers form a mesh using junctional complexes Junctional complexes formed from short actin filaments Cytoskeleton is linked to membrane through 2 transmembrane proteins, band 3 and glycophorin > provide way of keeping membrane in certain orientation + give the ability to stand up to some flexion > scaffold!

Question 533

How is membrane movement controlled?

Answer 533

A domain is formed if there is a physical blockage to movement Lateral diffusion is possible within a domain of the membrane Tight junctions are an example as they restrict movement within the bilayer > they require multiple proteins > makes sure there’s a mono-layer of plasma membrane > enables diffusion within the domain at the top but DOESN’T allow diffusion down the sides

Question 534

How is diffusion limited in the membrane?

Answer 534

The cortical cytoskeleton network restricts diffusion of plasma membrane proteins directly anchored to it Cytoskeletal filaments form mechanical barriers that obstruct free diffusion > partitioning them into small domains Proteins diffuse rapidly but are confined within an individual domain Transmembrane proteins associated with many other proteins are limited in their diffusion depending on interactions between them and size of its cytoplasmic domain

Question 535

What is the benefit of the formation of domains?

Answer 535

Helps concentrate signalling complexes, increasing the speed and efficiency of the signalling process Domains can be permanent (spermatozoa) or transient In cells with several structurally and functionally distinct parts, rafts enable domains of the membrane to form that contain specific proteins - eg in spermatozoa

Question 536

Glycolipids

Answer 536

Made of a diglyceride attached to a carbohydrate Diglyercide acts as the anchor Immune recognition Involved in determination of self / blood groups Important in surveillance of cells and tissues by macrophages + T cells > checking there aren’t any foreign particles like bacteria or viruses

Question 537

Glycoproteins

Answer 537

Usually part of complex, multi subunit receptors Carbohydrate chain acts to restrict movement or scaffold structures Eg - proteoglycans > essential for interaction with extracellular matrix

Question 538

What are the functions of glyco-additions?

Answer 538

Support interactions of a receptor with its ligand Can act as part of ligand recognition site

Question 539

Exocytosis

Answer 539

Vesicle moves to membrane and releases its contents

Question 540

Endocytosis

Answer 540

Sampling the extracellular environment > takes something up > ‘budding’ process in reverse > invagination of membrane > takes things up from outside

Question 541

What is the donor compartment?

Answer 541

Where cargo is and receptors that are needed to package vesicle Cargo associates with receptors > signals that there should be a bud forming ‘Budding’ process leads to production of vesicle

Question 542

Vesicle transport

Answer 542

Donor compartment first Vesicle is going towards target membrane Knows where it needs to go based on coat and snare proteins Vesicle fuses with membrane and fusion happens Contents of vesicles get released out into target compartment

Question 543

What do glyco additions like Mannose enable?

Answer 543

Receptor binding and direct transport to specific compartments

Question 544

Directions of movement for coat proteins: COPI, COPII and Clathrin

Answer 544

COPI - goes from Golgi to ER COPII - goes from ER to Golgi Clathrin - involved in uptake of things from outside of cell by endocytosis from plasma membrane into early endosome OR from some parts of Golgi out to endosome

Question 545

Lipids and compartments SUMMARY

Answer 545

Contents of membrane can be regulated by endocytosis and exocytosis Membrane components made in ER contain LOW levels of cholesterol, increasing as membrane matures through Golgi to plasma membrane Membrane bound proteins generated in ER can act as cargo receptors Vesicular transport enables secretory proteins and membrane bound proteins to be transported to plasma membrane while also allowing Retrograde Transport into the cell of extracellular environment, membrane recycling and receptor recycling and degradation

Question 546

Structure of Clathrin coats (Only recruited to receptors associated with plasma membrane)

Answer 546

Each Triskelion is composed of 3 Clathrin heavy chains and 3 light chains Light chains attach to cytoskeleton and is how the bending process starts! Because it requires an adaptor protein to bind to cytoskeleton that’s inside and helps generate a force due to its shape! Triskelion made of proteins > some AA in these will be charged > charge will help to bend membrane

Question 547

Coat formation steps

Answer 547

Coat assembly and cargo selection - proteins in ER membrane act as receptors to keep cargo in specific place. Binding leads to conformational change that enables adaptor proteins to be recruited Bud formation - adaptor proteins (eg AP2) bind to Clathrin Triskelions. Bar domain containing proteins aid the bending of membrane to increase access to adaptor proteins to Clathrin Vesicle formation - continuation of formation of a vesicle and generation of a stalk > then recruits Dynamin and accessory proteins to pinch off vesicle Uncoating - after vesicle released, there is NO longer need for coat proteins and associated proteins, so they are disassembled and recycled. This leaves the vesicle with cargo bound receptors on vesicle surface > and snare proteins to direct the vesicle to its destination

Question 548

Initiation of coat formation

Answer 548

Adaptor protein AP2 is made up of different subunits: B2, u2, o2. Binding of u2 and o2 needs to bind PIP2 to initiate cargo receptor binding PIP2 binds > changes shape > flips subunit around > unlocks it > AP2 now open Change in receptor conformation leads to membrane deformation, making it more accessible for coat proteins

Question 549

Coat proteins need help to bend the membrane

Answer 549

Membrane bending proteins that contain BAR domains cause a shape change to membrane via electrostatic interactions with lipid head groups BAR domain proteins are thought to help AP2 recruit Clathrin by shaping the plasma membrane to allow Clathrin costed bud to form Some proteins contain Amphiphilic helices that causes membrane bending when inserted into cytoplasmic leaflet These are essential to shaping the neck of budding vesicle through stabilisation of sharp membrane bends Clathrin machinery recruits local assembly of actin filaments that introduce tension to help pinch off and propel the forming vesicle away from the membrane

Question 550

Vesicle release

Answer 550

Dynamin recruits a protein complex to initiate vesicle release Inner leaflet of the bilayer merge, then the vesicles pinches off

Question 551

Dynamin

Answer 551

GTPase domain > will cleave GTP to GDP. If associated with GDP = relaxed structure. If exchanged to GTP > squeezes the neck of budding vesicle as it contracts > which hydrolyses GTP into GDP again. GDP will fall off, Dynamin relaxes and process repeats Dynamin had PIP2 binding site as well! So PIP2 used for recruitment of Dynamin and to allow adaptor proteins to bind to Triskelion

Question 552

Rab proteins and their role

Answer 552

Single protein monomeric GTPases > associate with GDP when not active and GTP when ACTIVE As vesicles approaches, there is tethering > Rab recognises Rab effector and guides it in Rab effector then changes shape to guide it to where snare is T snare and V snare are complementary to eachother = Trans snare complex. Bring the membranes close together to cause fusion. Rab GDP is then recycled, binds to Rab GDP inhibitor that stops it from working until it becomes associated with vesicles again! Cargo then released into target compartments

Question 553

Lipid droplets

Answer 553

Triaglycerols and cholesterol esters Generation of cholesterol through HMG CoA reductase > resident in the ER Products are NOT amphipathic > therefore need to be coated in membrane to enable transport through the aqueous cytosol Lipids are NOT hydrophilic so only need a single coating of membrane

Question 554

LDL uptake Excess LDL can control cholesterol synthesis in the liver. The detection system is as follows:

Answer 554

Endocytosis of LDL particles using Clathrin coated pits Recycling of LDL receptors to plasma membrane Formulation of a vesicle containing cholesterol esters which is integrated into ER High cholesterol levels in ER results in a decrease in the synthesis of HMG CoA reductase and LDL receptors

Question 555

Vesicle transport SUMMARY

Answer 555

Organelle and membrane makeup can be regulated by endocytosis and exocytosis Donor compartments require specific lipids (PIP2) to encourage recruitment of adaptor proteins to loaded cargo receptors during bud formation Recruitment of cost protein and associated BAR domain containing proteins bends the membrane to generate a vesicle which is released with the help of Dynamin Monomeric GTPases such as Rab hell to ensure the vesicles reaches its target. With its complementary Rab effector enables docking on target membrane to enable SNARE proteins to cause membrane fusion Endocytosis and exocytosis can be observed in the regulation of lipoprotein and cholesterol levels in the body through the LDL receptor feedback system

Question 556

Membrane asymmetry

Answer 556

Incoming vesicles to cell surface are randomly sorted = problem At cell surface there is phos ethanolamine and phos serine on the inner leaflet Scramblase is in the ER and ensures that there is the same number of phospholipids on outer leaflet as the inner leaflet Glycolipids are on outer leaflet for cell recognition

Question 557

Dealing with membrane asymmetry

Answer 557

Enzymes are required to ensure that membrane phospholipid addition occurs EQUALLY on both leaflets of the bilayer

Question 558

Scramblases

Answer 558

Calcium dependant enzymes Enables movement of phospholipids from inner to outer leaflet of plasma membrane Calcium will activate enzyme > allow it to change shape so it can move things from 1 side to the other Lots of Calcium in the ER > means scramblase is turned ON most of the time! Calcium concentration in plasma membrane is low > is not turned on under normal circumstances

Question 559

Scramblase action

Answer 559

Important in apoptosis Maintains mitochondrial membrane function In apoptosis, ER is compromised in integrity. So releases large volumes of calcium from ER into cytoplasm. When calcium levels increase in cell, it activates scramblase. Problematic as it allows phos serine to move to outer leaflet > it is negatively charged > means -ve charge is on outside of membrane instead! Problematic for mitochondria, cells can’t survive in this environment, no ATP etc

Question 560

Flippase and floppase

Answer 560

A helical structure Part of flippase family of proteins ATP binding cassette transporter protein

Question 561

Flippase and floppase action (Very specific)

Answer 561

Flippase - moves anything that is phos serine and phos ethanolamine onto the inner leaflet Floppase - moves other 2 phospholipids out to the outer leaflet / external surface So creates membrane asymmetry! ATP is essential for their function > problem if there’s no ATP, means flippase and floppase can’t correct Scramblase action > disrupts membrane symmetry > membrane compromised > disrupts cell function > APOPTOSIS

Question 562

What is the compound Fluorodeoxyglucose used for?

Answer 562

Detection of cancer tumours, using positron emission tomography PET

Question 563

List the characteristics of Hexokinase 4

Answer 563

Catalyses an irreversible reaction (uni directional) Is a control point in glycolysis Fructose 6 phosphate is an allosteric inhibitor Broad specificity for hexose monosaccharides Sigmoidal kinetics Activity is controlled by a regulator protein High KM and vmax for glucose Expressed in the liver and pancreas

Question 564

What hormone is linked to the feeding response and increases utilisation of glucose?

Answer 564

Insulin

Question 565

What products are produced during the pay off phase of glycolysis?

Answer 565

2x pyruvate 4x ATP 2x NADH

Question 566

What are the products of the reaction catalysed by PFK1?

Answer 566

Fructose 1,6 bisphosphate

Question 567

The conversion of fructose 6 phosphate to fructose 2,6 bisphosphate is catalysed by what enzyme?

Answer 567

PFK2

Question 568

Elevated levels of glycolysis in tumour cells are due to the …

Answer 568

Warburg effect

Question 569

Allosteric compounds can be identified by …

Answer 569

Sigmoidal kinetics

Question 570

Glucagon activates the … enzyme

Answer 570

FBPase 2

Question 571

What are the metabolic roles for NADPH

Answer 571

NADPH oxidase (phagocytosis) Reductive biosynthesis Phase 1 drug metabolism Reduction of hydrogen peroxide Nitric oxide synthesis

Question 572

In the synthesis of fatty acids, the addition of a 2 carbon unit requires …

Answer 572

2 NADPH

Question 573

What are the protective mechanisms against oxidative stress?

Answer 573

Superoxide dismutase SOD Vitamin C Glutathione peroxidase Vitamin E

Question 574

Regarding the G6PD enzyme, NADPH is a…

Answer 574

Product and product inhibitor!

Question 575

What intermediate in the PPP is utilised for synthesis of nucleic acids?

Answer 575

Ribose 5 phosphate

Question 576

When fats are ingested in the diet …

Answer 576

Bile salts emulsify dietary fats in the small intestine, forming mixed micelles Intestinal lipases degrade triaglycerols Fatty acids and other breakdown products are taken up by the intestinal mucosa and converted into triaglycerols Triaglycerols are incorporated with cholesterol and apolipoproteins into chylomicrons Chylomicrons move through the lymphatic system and bloodstream to tissues Lipoprotein lipase activated by apoC II in the capillary, converting triaglycerols to fatty acids and glycerol Fatty acids enter cells Fatty acids are oxidised as fuel or re esterified for storage