Metabolism Flashcards
(278 cards)
1
Q
Define the first law of thermodynamics.
A
The total energy within a system is constant. It can neither be created nor destroyed, but is converted from one form to another.
2
Q
In which forms do we store energy in the body?
A
TAGs
Glycogen
3
Q
What is the difference between anabolism and catabolism?
A
Anabolism= synthesising compounds, requires energy input by ATP hydrolysis Catabolism= breaking down compounds to obtain their stored energy (ADP phosphorylation)
4
Q
What is the basis of metabolism?
A
Carbon compounds in food are oxidised to form ATP.
5
Q
Give three examples of energy units.
A
Joule= energy required to push against 1N of force for 1m
cal (1cal = 4.184 J)
Cal (1Cal = 4.184 kJ)
6
Q
How is the energy content of foods measured?
A
Calorimetry gives Atwater factors: the energy value of a food in kJ/g
7
Q
Which foods’ energy can’t we access?
A
Fibre (cellulose) is lost in faeces
Nitrogen is not oxidised, excreted in urine
8
Q
How do we measure energy expenditure?
A
Direct calorimetry: measure heat output from an individual to determine BMR
Indirect calorimetry: measure O2 consumption and CO2 production using a respirometer
9
Q
How does measuring O2 consumption allow us to calculate energy expenditure?
A
A certain amount of energy is associated with every litre of O2 consumed.
We use the respiration exchange ratio:
RER= CO2 produced / O2 consumed
10
Q
What things do we spend energy on at rest?
A
Muscle contractions Nerve conduction Ion transport Macromolecule synthesis Maintenance of body heat
11
Q
Name four classes of macronutrients that provide energy, and what they are broken down into.
A
Carbohydrates- monosaccharides
Protein- amino acids
Fat- free fatty acids, MAG (monoacylglycerol), cholesterol
Nucleic acids- nucleotides
12
Q
How is carbohydrate chemical digestion initiated?
A
Salivary amylase produced by salivary glands.
13
Q
What do the chief cells of the gastric glands secrete?
A
Pepsinogen –> pepsin for protein digestion
14
Q
What are the functions of the pancreas and liver?
A
Pancreas- secretes digestive enzymes (amylase, lipase and proteases)
Liver- synthesises bile for fat digestion
15
Q
Describe the two main phases of digestion.
A
Hydrolysis of covalent bonds connecting monomer units in food macromolecules.
- glycosidic bonds (starch to disaccharides)
- peptide bonds (to smaller peptides)
- triacylglycerol ester bonds (to fatty acids)
Absorption of products from GI tract into the body.
16
Q
Describe the structure of cellulose, and why we cannot digest it.
A
Repeating cellobiose units. We don’t have an enzyme that can hydrolyse the beta (1 to 4) glycosidic bonds between cellobiose units.
17
Q
Why are some people lactose intolerant? Why do they get bloating symptoms?
A
They don’t have the enzyme lactase to hydrolyse the beta (1 to 4) glycosidic linkages between lactose units.
Fermentation of lactose by intestinal bacteria.
18
Q
What is sucrose made up of?
A
Glucose and fructose
19
Q
Name six enzymes involved in carbohydrate digestion, and where they are synthesised.
A
Salivary amylase- salivary glands Pancreatic amylase- pancreas Maltase- small intestine Lactase- small intestine Sucrase- small intestine Isomaltase- small intestine
20
Q
Describe the structure of starch.
A
Made up of amylose- linear polymer of alpha (1 to 4) linked glucose units
and amylopectin- branched polymer of alpha (1 to 4) linked glucose units, and alpha (1 to 6) linked glucose units
21
Q
Describe the molecule animals synthesise which is similar to starch.
A
Glycogen- has similar branched structure to amylopectin
Synthesised from glucose and stored in liver and muscle, then broken down when the body needs energy.
22
Q
How is starch chemically digested in the body?
A
Amylase in the mouth and stomach hydrolyses the alpha (1 to 4) glycosidic bonds until the starch is broken down into maltose and isomaltose disaccharides.
Intestinal epithelium secretes maltase and isomaltase to break glycosidic linkages of maltose and isomaltose into glucose monomers.
23
Q
What does lactose get digested into?
A
Galactose and glucose
24
Q
What are dextrins?
A
Small hydrolysed fragments of starch (mid-digestion).
25
Name three functions of protein digestion.
Supplies essential amino acids that the body doesn't make.
Supplies nitrogen for purines, pyrimidines and haem units.
Can use carbon skeletons for fuel.
26
Describe Kwashiorkor.
Swelling of the abdomen due to lack of dietary protein, osmotic imbalance in the GI system, and water retention. Also affects molecule transport.
27
How are proteases secreted and activated?
Secreted as inactive forms (zymogens/ proenzymes), and activated by cleavage of peptides from their structure
28
How do pepsin, trypsin and chymotrypsin show specificity?
Pepsin and chymotrypsin bind aromatic side chains.
Trypsin binds positively charged side chains.
The side chain they bind is the one next to the oxygen of the peptide bond to be cleaved.
29
Describe the two stages of protein digestion.
Endopeptidases attack peptide bonds within the protein polymer: pepsin, trypsin, chymotrypsin
Exopeptidases attack peptide bonds at the end of the protein polymer: aminopeptidases (from N-terminal) and carboxypeptidases (from C-terminal)
30
Name six enzymes involved in protein digestion, where they are synthesised, and what they cleave.
Pepsin- stomach mucosa- proteins, pepsinogen
Trypsin- pancreas- polypeptides, chymotrypsin
Chymotrypsin- pancreas- polypeptides
Carboxypeptidase- pancreas, polypeptides
Aminopeptidase- small intestine, polypeptides
Dipeptidase- small intestine, dipeptides
31
Pepsin acts in the stomach, where do the other proteases act?
Small intestine
32
Describe the two ways pepsinogen is activated to pepsin.
Autolytic activation: Being exposed to the acidic environment of the stomach, pepsinogen partially unfolds and is hydrolysed.
Catalytic activation: Pepsin hydrolyses other pepsinogen molecules to activate them to pepsin.
33
Name the zymogen forms of carboxypeptidase, chymotrypsin, and trypsin. Where are they secreted?
Procarboxypeptidase
Chymotrypsinogen
Trypsinogen
Through the pancreatic duct into the intestinal lumen.
34
Give two examples of molecules associated with fat metabolism.
Triacylglycerol
| Cholesterol
35
Describe bile salts.
Acids synthesised from cholesterol in the liver and stored in the gallbladder as bile. Secreted into the small intestine in response to cholecystokinin.
36
What do bile salts do for triacylglycerols?
Solubilise them- as they are hydrophobic- by forming micelles with them. This also increases surface area for their digestion.
37
What does bile contain?
- water
- bile acids
- electrolytes
- phospholipids
- cholesterol
- bile pigments
38
How do the bile salts glycocholic acid and taurocholic acid differ from cholesterol structurally?
They have a modified functional group.
39
What are gallstones caused by?
High concentration of bile and cholesterol in the gallbladder.
40
What stimulates gastrin release, and what does it stimulate?
Stimulated by the presence of protein-containing food in the stomach. Stimulates secretion of gastric juices.
41
What stimulates secretin release, and what does it stimulate?
Stimulated by HCl in the duodenum. Stimulates secretion of alkaline bile and pancreatic fluids.
42
What stimulates cholecystokinin release, and what does it stimulate?
Stimulated by fats and amino acids in the duodenum. Stimulates release of pancreatic enzymes and release of bile from the gallbladder.
43
Describe digestion of lipids from arrival in the duodenum to absorption.
1. Emulsified by bile salts to form micelles.
2. Pancreatic lipase/ colipase enzyme complex binds to lipid/aqueous interface.
3. Pancreatic lipase hydrolyses TAG to free fatty acids at 1 and 3 positions, and 2-monoacylglycerol
4. Smaller micelles form, containing bile salts, free fatty acids, monoacylglycerol and cholesterol.
5. Micelles are absorbed across intestinal cell membrane.
44
Does the pancreatic lipase enter the micelle?
Just the catalytic part extends inside to carry out hydrolysis.
45
How is absorption increased in the small intestine?
Villi and microvilli brush border.
46
What is fat malabsorption? What's it caused by?
Decreased intestinal absorption of fat, leading to excess of fat and fat soluble vitamins in the faeces. Caused by conditions that interfere with pancreatic lipase or bile secretion.
47
What is Xenical/Orlistat, and its consequence?
A potent inhibitor of pancreatic lipase- forms a covalent bond. This leads to less uptake of fats as fatty acids and monoacylglycerol (fat malabsorption).
48
Once lipids are absorbed into the epithelial cell, what further processing occurs?
sER converts fatty acids and monoacylglycerol back into triacylglycerol. rER produces apoB. Golgi processes these into chylomicrons, which are excreted into the lymph and then carry TAGs through the bloodstream.
49
What are lipoproteins and apoproteins?
Lipoproteins solubilise lipids for transport in blood to tissues. They provide a delivery system for transporting lipids into and out of cells. Apoproteins are the protein components associated with the particular lipoprotein.
50
Name three functions of apoproteins.
Assembly of lipoprotein: apoB
Act as ligands for receptors: apoE and apoB
Enzyme cofactors: apoCII for lipoprotein lipase
51
Describe the general structure of a lipoprotein.
Layer of phospholipids forming amphipathic wall of giant micelle. TAGs and cholesterol inside. Apoproteins form part of the wall.
52
Name the four lipoprotein classes in order of lowest to highest density. Which has the highest proportion of lipid?
Chylomicrons (highest lipid proportion)
Very low density lipoproteins VLDL
Low density lipoproteins LDL
High density lipoproteins HDL
53
How is lipoprotein composition clinically analysed?
By non-denaturing/ native electrophoresis.
54
Name the two major lipid transport pathways.
Exogenous chylomicron pathway (dietary fat)
| Endogenous VLDL/LDL pathway (synthesised fat)
55
How do chylomicrons affect the appearance of the blood?
Give it a milky colour after a fat-rich meal.
56
Describe the endogenous VLDL/LDL pathway.
Lipoprotein lipase in peripheral tissues releases the fatty acids for use in tissue, leaving the remnants of the chylomicrons circulating in the bloodstream. ApoE receptor in liver cells picks up these remnants and repurposes them to form VLDL, then again for LDL.
57
Where are the highest activities of lipoprotein lipase? What is it activated by?
Heart and skeletal muscle. apoCII
58
What do defects in apoCII (familial Apo CII deficiency) and lipoprotein lipase lead to?
Elevated levels of chylomicrons and plasma triacylglycerol.
59
How do we estimate VLDL and LDL in the lab?
VLDL=TAG/5
| LDL=Total cholesterol - HDL - VLDL
60
What is familial hypercholesterolemia? What is it caused by?
High level of fat in the blood, resulting in premature atherosclerosis (fat building up in artery walls). Caused by dominant mutation in LDL receptor gene- makes LDL levels 2 to 3x higher than normal.
61
What are xanthomas?
Fatty growths under the skin in people with familial hypercholesterolemia.
62
What do sugars require to travel across cell membranes, and why?
Specific transporter proteins that form pores/ channels in the membrane. They can't just diffuse across the membrane because they are highly water soluble.
63
Name the two types of sugar transport across a cell membrane. Name a transporter for each type that moves glucose across the intestinal epithelia.
Active transport- requires ATP to move sugar down its concentration gradient.
- SGLT 1
Facilitative transport- passage down the concentration gradient.
- GLUT 2
64
Describe SGLT 1.
A membrane protein on intestinal epithelial cells that allows glucose/ Na+ symport. It transports Na+ down its concentration gradient, while co-transporting glucose. No energy required.
65
Describe GLUT 2.
Facilitative transporter which allows glucose to move down its concentration gradient out of the intestinal cell, across the basal membrane and into the bloodstream.
66
Why is Na+/K+ ATPase also required for glucose transport? Describe its process.
Na+/K+ ATPase maintains low intracellular Na+ so SGLT 1 can function. ATP is hydrolysed and the protein is phosphorylated, leading to conformational change and transport of 3 Na+ out of the cell. Protein is dephosphorylated, changes conformation and transports 2 K+ into the cell.
67
Name two other glucose transporters in the body, and their locations.
GLUT 3- transports glucose in the brain
| GLUT 4- transports glucose in muscle and adipose
68
In which forms are proteins absorbed by the intestinal epithelia?
Di- and tri-peptides (no longer than four aa's)
| Individual amino acids
69
Describe absorption of di- and tri-peptides from the small intestine.
Membrane transporter PepT1 co-transports the peptides with H+ ions. They are further digested into amino acids by cytoplasmic peptidases, then exported into the blood circulation.
70
Describe absorption of individual amino acids from the small intestine.
Na+-dependent carriers transport Na+ and an amino acid across the brush border. There are at least six different carriers (for acidic aa's, basic, neutral etc.). Na+/K+ ATPase maintains low intracellular Na+. Amino acids diffuse into blood circulation through facilitated transporter.
71
When are full proteins absorbed from the GI tract?
In newborns- uptake of immunoglobulins gives passive immunity.
72
Describe the cause of pancreatitis.
Inappropriate activation of zymogens, resulting in self-digestion- degrading proteins of the pancreas.
73
Describe the cause of stomach/ peptic ulcers.
Breakdown of the mucosa which normally protects against protease action.
74
Describe how cystic fibrosis causes pancreatic issues.
Thick mucous secretions block the pancreatic duct and secretion of pancreatic enzymes. (can be aided by taking supplements containing those enzymes)
75
Describe the cause of coeliac disease, and how this affects the GI tract.
Antibodies react with transglutaminase, and body reacts against gluten protein. Villi are flattened and nutrients aren't absorbed as efficiently.
76
Describe the digestion of nucleic acid polymers.
DNA and RNA are hydrolysed in the stomach by HCl. In the intestine, endonucleases hydrolyse the phosphodiester bonds, and exonucleases release individual nucleotides (nucleoside monophosphates).
77
What are four ways we can test if we get enough vitamins and minerals?
Clinical examination/ look for symptoms
Anthropometry/ energy balance and growth
Biochemical tests (blood test)
Dietary assessment
78
How do vitamins and minerals differ?
Vitamins are essential organic molecules, while minerals are essential inorganic molecules. If vitamins are low in the diet, symptoms of deficiency appear, whereas they might not appear with low minerals.
79
What is bioavailability in terms of vitamins and minerals?
The amount of the molecule ingested that can be absorbed and used.
80
Name the groups of vitamins.
```
Fat soluble (A, D, E, K)
Water soluble (C, B group)
- B group: 1, 2, 3, 5, 6, 7, 9, 12
```
81
Define fortification.
Addition of nutrients (vitamins or minerals) to food.
82
Where do we source vitamin D?
From food (egg yolks, fatty fish) and we produce it ourselves when exposed to sunlight.
83
What is the key role of vitamins and minerals in the body?
Coenzymes and cofactors.
84
What does a thiamin (B1) deficiency cause?
Buildup of lactate and subsequent venous pooling.
85
What are calcium and vitamin K important for?
Blood clotting
86
Magnesium is an essential cofactor for which enzymes?
Kinases
87
Tryptophan undergoes a series of reactions before reacting with which B-vitamin to form NAD?
Niacin/ nicotinic acid (B3)
88
What is NAD involved in within the body?
Carries out oxidation and reduction reactions, involved with synthesis and breakdowns of carbohydrates, lipids, and amino acids.
89
Describe pellagra.
The result of a cellular deficiency of niacin (B3), due to inadequate intake of either tryptophan or niacin. Four D symptoms: dermatitis, diarrhea, dementia, and death.
90
Which three minerals are low in NZ soils?
Iodine, fluoride, and selenium.
91
Name an example of a structural role of minerals.
Hydroxyapatite crystal in dental enamel: calcium and phosphorus
92
What is the role of magnesium in the body?
It is a cofactor for >300 enzymes e.g. kinases
Stabilises proteins, nucleic acids and membranes
Electrolyte
Bone metabolism and remodelling
Nerve impulse and muscle contraction
93
What is the role of ATP in cell?
The energy intermediate/ currency
94
Explain the Gibb's energies of ATP hydrolysis and synthesis. Which component of metabolism are the associated with?
G(hydrolysis)= -30kJ/mol
- energetically favourable, releases energy (anabolism)
G(synthesis)= +30kJ/mol
- energetically unfavourable, requires energy (catabolism)
95
What does ΔG°' mean?
Gibbs energy under standard conditions (all reactants at 1M, except H+ because pH=7)
96
How do enzymes drive necessary, yet unfavourable reactions? Give an example.
By coupling them to favourable reactions.
Glycolysis (+14) coupled to ATP hydrolysis (-30)
- driven by hexokinase, adds phosphate to glucose
97
Name the two key types of reactions in food processing pathways.
```
Those involving ATP and ADP
Redox reactions (fuel molecules are oxidised)
```
98
What is the basis of a redox reaction?
Reducing agent is oxidised- loses electrons
| Oxidising agent is reduced- gains electrons
99
What kind of oxidation occurs in food processing pathways?
Stepwise oxidation of fuel molecules- releasing lots of energy for production of ATP.
100
What is reduced in the redox reactions of the food processing pathways?
Coenzymes: NAD+ and FAD
101
How is hydrogen involved in biological redox reactions?
They often involve the transfer of hydrogen atoms (which includes the electron).
H = H+ + e-
Hydrogen is a 'reducing equivalent'
102
Which enzymes often catalyse biological redox reactions?
Dehydrogenases
103
Describe coenzymes.
Small organic molecules that exist in two forms.
Subclass of co-factors, often derived from vitamins.
Low concentration in the cell, act as carriers.
104
What does NAD stand for? Which vitamin is it derived from?
Nicotinamide adenine dinucleotide
| Niacin (B3)
105
How does NAD+ turn into NADH?
Undergoes a two electron reduction. Accepts two electrons, and one H+.
106
What does FAD stand for? Which vitamin is it derived from?
Flavin adenine dinucleotide
| RIboflavin (B2)
107
Where are FAD and NAD located in relation to their associated enzymes?
NAD interacts with the enzyme during the reaction, then is released into solution.
FAD is tightly bound to the enzyme with which it interacts- it stays there after the reaction.
108
How does FAD turn into FADH2?
It undergoes a two electron reduction. Accepts two electrons, and two H+.
109
Describe CoA.
Coenzyme A is an important coenzyme in the metabolic pathways. Derived from pantothenic acid (B5), and carries acyl groups. It is not reduced or oxidised (doesn't carry electrons). Has two forms: CoASH (free CoA), and Acyl-CoA.
110
How does CoASH turn into acyl-CoA?
Acyl group attaches to coenzyme via the sulfur atom- so there is no longer a free SH group.
111
What happens to glucose in glycolysis? Where and in which cells does it occur?
It's oxidised.
In the cytoplasm (in eukaryotes), unlike the other metabolic pathways. All cells use glucose as fuel, but some depend on it:
- RBCs (no mitochondria)
- brain cells (easier to supply/ safer)
- eye (anaerobic because blood vessels needed which would refract the light)
- white muscle cells (anaerobic)
112
Describe the basis of glycolysis (what do we end up with?).
The splitting of glucose (6C) into two pyruvate molecules (3C). Energy is released and conserved in ATP and NADH.
113
Describe the two phases of glycolysis.
Energy investment phase- activating glucose by putting energy in
Energy payoff phase- making an ATP profit
114
When does splitting of the glucose molecule occur in glycolysis, in relation to the two phases?
At the end of the investment phase.
115
In the first step of glucose activation from glucose to glucose-6-phosphate, why do we use ATP?
Because this reaction is energetically unfavourable without coupling it to ATP hydrolysis.
116
From G-6-P to fructose-6-phosphate, the ΔG˚'= +1.6 . How can this reaction proceed without the help of ATP?
This is the delta G under standard conditions. Under cellular conditions, the reaction is energetically favourable.
117
What is the aldolase reaction of glycolysis?
The 'splitting' reaction.
| FBP into DHAP and G-3-P
118
How do the structures of dihydroxyacetone
| phosphate (DHAP) and glyceraldehyde 3-phosphate (G-3-P) resemble each other?
They each have three carbons, and one phosphate.
119
What are two types of reactions that can synthesise ATP?
```
Those involving ADP and ATP (substrate-level phosphorylation, and oxidative phosphorylation)
Redox reactions (fuel is oxidised)
```
120
What kind of ATP/ADP reactions occur in glycolysis?
Substrate-level phosphorylation, where the energy comes from cleaving the phosphoanhydride bond on the substrate, and ADP goes to ATP.
121
Which non-ATP step in glycolysis is key for making an ATP profit and why?
G-3-P to 1,3-BPG (oxidised)
- a phosphate is added, powered by oxidation- no ATP required
NAD+ is reduced to NADH
122
How does arsenic poison glycolysis?
Arsenate substitutes for phosphate in G-3-P (similar molecules). It is very unstable, so the energy isn't captured when it's hydrolysed, and ATP isn't synthesised- no net gain of ATP. This is crucial for cells relying on glycolysis e.g. RBCs
123
Under aerobic conditions, what pathway can pyruvate feed? Describe the reaction occurring in between.
Citric acid cycle.
Oxidised to acetyl-CoA by pyruvate dehydrogenase in the mitochondrial matrix. Reaction is called an oxidative decarboxylation.
- the energy from oxidation is captured in NADH and used to add CoA
124
Under anaerobic conditions, which pathways can pyruvate feed?
```
Anaerobic glycolysis (mammals)
- pyruvate is converted into lactate, NADH is oxidised to NAD+
Anaerobic alcoholic fermentation (yeast)
```
125
What benefit does anaerobic glycolysis have for the cell?
The cell has a low concentration of coenzymes. Lactate formation allows for the regeneration of NAD+ after glycolysis has used it in the redox reaction (G-3-P to 1,3-BPG).
- in fact, all pyruvate pathways do this
126
What is the preferred fuel for most tissues?
Fatty acids
127
How much of our body weight does fat make up and why?
5-25%
| Because it is our primary energy reserve- any excess fats or glucose consumed is stored as TAGs.
128
Why do we store fuels as fats instead of glycogen?
Glycogen is approximately 2/3rds water, so takes up more space than TAGs. Fatty acids are more reduced than carbohydrates- more potential energy to be released when oxidised in metabolic pathways.
129
How do we mobilise stored TAGs for use as fuel? Which proteins are required?
Lipase cleaves it into free fatty acid and glycerol, which passively diffuse into the blood. Glycerol travels to the liver.
Albumin transports the FFA in its hydrophobic pocket to the tissues. Fatty acid binding protein FABP (beta sheets form a barrel with a hydrophobic core) transports the FFA across the cell membrane.
130
Describe fatty acid activation (before fatty acid oxidation).
Occurs before the fatty acid enters the mitochondria.
| Acyl-CoA synthetase attaches CoA to the fatty acid to make fatty acyl-CoA. Requires hydrolysis of ATP to AMP.
131
What is the difference between fatty acyl-CoA and acetyl-CoA?
A fatty acyl-CoA includes a carbon chain of any length. Acetyl-CoA is a type of fatty acyl-CoA with a two-carbon chain.
132
How are fatty acids transported into the mitochondrial matrix?
1. Diffuses through fatty acyl-CoA carrier on outer membrane into intermembrane space.
2. Carnitine acyltransferase converts it to fatty acyl-carnitine by swapping CoA for a carnitine.
3. Diffuses through carrier protein on inner membrane to the matrix.
4. Carnitine acyltransferase carries out the reverse reaction, converting it back into fatty acyl-CoA.
133
Which fatty acids undergo beta-oxidation?
Ones with an even number of carbons- saturated (no double bonds).
134
Where does the released energy go in beta-oxidation?
Transferred to coenzymes NAD and FAD.
135
What is the basis of beta-oxidation?
Cut the carbon chain into two pieces- acetyl-CoA goes into citric acid cycle, and other piece goes back into the cycle to be cut at the next place.
136
Describe the first three steps of beta-oxidation.
1. Oxidation--> form double bond between alpha- and beta-carbons, reduce FAD to FADH2
2. Hydration --> add OH to beta-carbon, and H to alpha-carbon
3. Oxidation--> form double C=O bond on beta-carbon, reduce NAD+ to NADH, H+
137
What is the purpose of steps 1-3 in beta-oxidation?
Rearranging the molecule to allow the bond to be cleaved, capturing energy in coenzymes.
138
Describe the fourth step of beta-oxidation.
Acetyl-CoA is released to go into the citric acid cycle. A free CoASH is added to the carbon chain (which is 2C shorter), and it undergoes beta-oxidation again.
139
How do we calculate the amount of NADH, FADH2 and acetyl-CoA produced from all the rounds of beta-oxidation?
(no. of C/2) - 1 for NADH and FADH2
| (no. of C/2) for acetyl CoA
140
Where does the citric acid cycle occur? Where are all the enzymes and substrates?
In the mitochondria
| In the mitochondrial matrix (except for one enzyme- succinate dehydrogenase)
141
For each acetyl-CoA that enters the CAC, how much energy is captured, and in what forms?
1 ATP, 3 NADH, 1 FADH2
142
In which forms does carbon enter and leave the CAC?
Enters as acetyl-CoA (2C)
| Leaves as 2CO2
143
Name the two parts of the CAC.
Release of carbon.
| Regeneration of the starting molecule (oxaloacetate).
144
When acetyl-CoA enters the CAC, citrate synthase adds the acetyl to oxaloacetate to form citrate. Where does this enzyme get the energy for this reaction?
From the hydrolysis of CoA from acetyl-CoA.
145
What is the purpose of the converting citrate to isocitrate?
It makes the molecule more susceptible to decarboxylation (we need to get rid of the 2 carbons that entered- since it's a cycle).
146
How does fluoroacetate (1080) poison the CAC?
Citrate synthase can't tell fluoroacetyl-CoA apart from acetyl-CoA, and forms fluorocitrate. When aconitase tries to rearrange fluorocitrate, it binds tightly to the enzyme, deactivating it.
Deactivating this enzyme not only inhibits further steps of the CAC from occurring, but causes a buildup of acetyl-CoA, inhibiting previous pathways (beta-oxidation and glycolysis).
147
What is the name of reaction that isocitrate dehydrogenase performs in the CAC? Name the two steps.
Oxidative decarboxylation
Oxidation- form double C=O bond and reduce NAD+ to NADH
Decarboxylation- remove carboxyl group (CO2)
148
How does alpha-ketoglutarate dehydrogenase add CoA to alpha-ketoglutarate? What have we achieved by this stage in the CAC?
Uses the energy released from the cleavage of the carboxylic acid group to give CO2 (oxidation).
Removal of 2C and regeneration of a 4C molecule (first part completed).
149
What is the energy from the removal of CoA used for in the succinyl-CoA synthetase step of CAC? What kind of reaction is this?
To drive synthesis of GTP.
Substrate-level phosphorylation
150
In substrate-level phosphorylation, what needs to come from the substrate: phosphate, or energy?
Energy
151
What are the reactions used to convert succinate to oxaloacetate (CAC) similar to?
1,2,3 of beta-oxidation
152
Describe the reactions used to convert succinate to oxaloacetate in the CAC.
1. Oxidation- lose 2H from succinate and form double C=C bond, reducing FAD to FADH2
2. Hydration- add OH to one carbon and H to the other of the double bond (becoming single bond) of fumarate
3. Oxidation- lose 2H from malate and form double C=O bond, reducing NAD to NADH, H+
153
Why is succinate dehydrogenase SDH not in the mitochondrial matrix?
It uses FAD as a coenzyme- remains tightly bound to SDH. FADH2 needs to be oxidised back to FAD, so SDH needs to be a part of the electron transport chain as well- hence why it's bound to the inner mitochondrial membrane.
154
What process must amino acids undergo before they can be used as fuel?
Deamination
155
Describe deamination of an amino acid.
Removes amino group, generating a carbon skeleton to be used for energy, and a free amino group/ ammonium ion to be excreted.
156
Name two ways an amino acid can deaminated.
Release of amino group to solution, catalysed by an enzyme (e.g. glutamate dehydrogenase for glutamate).
Transamination- transfer of amino group to a keto acid.
157
Which enzymes and coenzyme are required for transamination reactions?
```
Aminotransferase enzyme/ transaminase
Pyridoxal phosphate (pyridoxamine phosphate with amino group)
```
158
What is pyridoxal phosphate derived from?
Vitamin B6
159
How does pyridoxal phosphate facilitate transamination reactions (2 steps)?
1. Amino group is transferred from amino acid to pyridoxal phosphate.
2. Amino group is transferred from pyridoxamine phosphate to the keto acid.
160
What is the amino acid converted to after a transamination reaction?
Keto acid
161
What do keto acids have to do with metabolic pathways?
They can be fed directly into them, or some require modification first. Keto acid = carbon skeleton of amino acid.
162
Apart from preparing carbon skeletons for use as fuel, what else are aminotransferases required for in the body?
Removing excess (toxic) nitrogen (NH4+ ammonium) via the liver.
163
Describe how aminotransferases allow NH4+ to be transported to the liver.
1. Form glutamate by adding NH4+ to alpha-ketoglutarate.
2. Form alanine by transamination of glutamate, adding NH4+ onto pyruvate.
3. Transport alanine in bloodstream which is picked up by liver cells.
4. Form glutamate by transamination of alanine, adding NH4+ onto alpha-ketoglutarate.
5. Deamination of glutamate into NH4+ and alpha-ketoglutarate.
(then NH4+ is detoxified into urea for excretion)
164
Which two reactions are coupled to carry out oxidative phosphorylation? What allows their coupling?
Electron transport through the ETC
Phosphorylation by ATP-synthase of ADP to ATP
Proton gradient- ETC makes it, ATP-synthase uses it.
165
Where is the ETC and why (2)?
Inner mitochondrial membrane, to provide a barrier for proton gradient- membrane is impermeable to H+. Also has access to reduced coenzymes of metabolic pathways in the matrix.
166
Describe the experiment that proved the ETC is in the inner mitochondrial membrane.
1. Cells homogenised in buffered sucrose.
2. Homogenate centrifuged at 1000 xg to separate debris and nuclei from lighter supernatant.
3. Supernatant centrifuged at 700 xg to separate mitochondria from lighter parts.
4. Treat mitochondria with mild detergent to remove outer membrane.
And ETC still works without the outer membrane.
167
Where do electrons for the ETC come from, and what do they ultimately reduce?
Reduced coenzymes NADH and FADH2 ultimately reduce O2 to H2O.
168
Describe the structure of the ETC.
Four complexes: I, II, III, IV
- all except II are transmembranous, II is partially inserted from matrix side
Two mobile carriers: ubiquinone UQ/ coenzyme Q CoQ, and cytochrome c cyt c
169
How are electrons shuttled through the ETC between carriers?
Each carrier accepts electrons/ is reduced in one redox reaction. And in the next redox reaction it donates electrons to/ is oxidised by a carrier with a higher reduction potential.
170
How is energy released via redox reactions between carrier in the ETC?
Each carrier has a lower delta G than the previous carrier, so energy is released in each redox reaction.
171
What is the energy released in redox reactions of the ETC used for?
Pumping protons across the inner membrane into the intermembrane space. (done by I, III, and IV)
172
Describe flow of electrons through the ETC from NADH.
NADH --> Complex I --> CoQ/UQ --> Complex III --> cyt c --> Complex IV --> O2
173
Describe flow of electrons through the ETC from FADH2.
FADH2 --> Complex II --> CoQ/UQ --> Complex III --> cyt c --> Complex IV --> O2
174
Name three inhibitors of electron flow through the ETC, and which part they inhibit.
- rotenone- inhibits e- transfer from I to CoQ
- cyanide- binds to a carrier in IV
- carbon monoxide- binds to O2 binding site on IV
175
What effects does stopping electron flow in ETC have?
- no proton gradient formed- no ATP made
- build-up of reduced coenzymes- providing no oxidising power for metabolic pathways
- reactive oxygen species produced (partially reduced O2) by reduced carriers passing electrons on in an uncontrolled manner- cause damage to membranes, DNA etc.
176
Where can UQ/CoQ move?
Within the inner mitochondrial membrane.
177
Does UQ/CoQ move one or two electrons?
Accepts two electrons from complexes I and II, and releases one electron at a time to complex III (called the Q-cycle).
178
Where can cytochrome c move?
On the outer surface of the inner mitochondrial membrane.
179
Does cyt c move one or two electrons?
One- from complex III to IV
180
How do UQ/CoQ and cyt c differ in how they carry electrons?
UQ/CoQ undergoes two-electron redox reactions, while cyt c contains a haem group that undergoes reversible Fe2+/Fe3+ redox reactions (one electron).
181
How many protons are pumped by each complex in the ETC for each coenzyme?
```
I= 4H+
II= 0
III= 4H+
IV= 2H+
```
(NADH 10H+, FADH2 6H+)
182
For each coenzyme in the ETC, how many O2 are reduced, and how many H2O are made? Biologically, what occurs?
1/2O2 + 2H+ --> H2O
Complex IV waits until it has four electrons- two coenzymes have been oxidised:
O2 + 4H+ --> 2H2O
- because O2 can't be 1/2
183
Define the pmf, and what creates it.
Proton-motive force is an electrochemical gradient that drives ATP synthesis. It is a result of:
- chemical/ pH gradient as a result of different H+ concentrations on either side of the membrane
- electrical gradients as a result of the charge difference across the membrane (more H3O+ in intermembrane space)
184
When mitochondria is isolated from cells and treated with detergent, what can we deduce about ATP synthesis?
Mild detergent removes outer membrane. Even though the ETC still works, ATP synthesis doesn't, because it needs the outer membrane to use the proton gradient.
185
Give two examples (other than treating mitochondria with mild detergent) that prove ATP synthesis requires a proton gradient/ pmf.
- use of bacteriorhodopsin (light inducible proton pump) in an artificial liposome- ATP is made when light is switched on (doesn't need ETC)
- no ATP is made when DTP (uncoupler- shuttles H+ back to the matrix) is present
186
How does the presence of DNP cause overheating of the internal organs?
Inhibits ATP synthesis, because it gets rid of the proton gradient, resulting in no pmf. The cell detects it's not making any ATP, so it feeds more fuel molecules through the pathways. It ends up burning lots of fuel molecules, and the energy can't be converted to ATP, so is released as heat.
187
Name the two components of ATP synthase, and their locations.
F1- matrix
| Fo- inner mitochondrial membrane
188
What does linking fluorescent actin to an immobilised ATP-synthase show?
Rotation of filament displays rotary mechanism of enzyme.
189
Define the two groups of subunits in ATP synthase.
Rotor subunits- ones that spin (c subunits and gamma stalk)
| Stator subunits- ones that stay stationary
190
What drives rotor movement of ATP synthase?
Protons flow from intermembrane space, through a proton channel to interact with c-subunits. This interaction causes a conformational change, which causes the rotor to spin. This exposes another proton (interacting with a different c-subunit) to the other end of the proton channel so it can move down its concentration gradient into the matrix.
191
How does the rotor movement drive ATP synthesis in the stator of ATP synthase?
The gamma-stalk rotates with the motor, which connects to the three alpha and beta subunit pairs, inducing a conformational change (they don't rotate).
192
Describe the conformational changes in alpha beta dimers caused by the rotor in ATP synthase.
Each dimer changes to the next state with each turn of the rotor.
- O open leads to release of ATP/ binding of ADP + P
- L loose holds ADP + P in preparation for catalysis
- T tight leads to ATP formation
193
How many protons need to be pumped to produce 1 ATP? How much ATP is made from proton pumping due to oxidation of NADH, and FADH2?
4
NADH (10 H+) = 2.5 ATP
FADH2 (6H+) = 1.5 ATP
194
How does alcohol (mechanically) affect the nervous system?
Binds to the GABAa receptor (ligand-gated Cl- channel), activating it. The channel selectively conducts Cl- ions causing an inhibitory effect on neurotransmission (dampens responses to other stimuli).
195
What other molecules bind to the GABAa receptor? (2)
GABA (gamma-aminobutyrate)- neurotransmitter derived from glutamate
Sedatives (benzodiazepines, barbiturates)
196
How much energy can be derived from ethanol?
29 kJ/g
197
Name the steps of alcohol metabolism (3), the enzymes catalysing them, and the coenzymes required.
1. Ethanol --> acetaldehyde (alcohol dehydrogenase)
- NAD oxidises
2. Acetaldehyde --> acetate (aldehyde dehydrogenase)
- NAD oxidises
3. Acetate --> acetyl-CoA (acetyl CoA synthetase)
- ATP and CoA required
198
Which step of alcohol metabolism is the fastest, and why?
Acetaldehyde --> acetate (catalysed by aldehyde dehydrogenase), because acetaldehyde is toxic.
199
What differs between the two forms of aldehyde dehydrogenase?
Their location: cytosol, and (most in) mitochondria
200
What does a red facial flush indicate (when drinking alcohol)?
A variant in the gene coding for the mitochondrial aldehyde dehydrogenase, which makes the enzyme work more slowly. Flush is caused by the buildup of acetaldehyde.
201
What occurs if we don't need the extra acetyl-CoA produced from alcohol metabolism?
Liver cells convert it into 16C fatty acids--> too much leads to steatosis (fatty liver disease)
202
When we add alcohol metabolism to the other pathways, what changes in our products?
More ATP, more NADH compared to NAD+
| Extra acetyl-CoA converted to fatty acids- esterified to TAGs- high cholesterol and TAGs in the blood, and fatty liver
203
What are the consequences of more NADH to NAD+?
```
All pathways slowed down.
Pyruvate converted to lactate (using up NADH + H+ --> NAD+)
- makes blood acidic
Inhibits gluconeogenesis of the liver
- hypoglycaemia
- coma
```
204
Describe the microsomal ethanol oxidising system. What else can it do (2)?
The alternative way to metabolise alcohol. Uses oxidase of the rER. Converts ethanol --> acetaldehyde by reducing NADPH + O2
- also metabolises other drugs
- can give rise to reactive oxygen species
205
What is alcoholic hepatitis, and what does it cause?
Excess inflammation in the liver due to fatty acids from alcohol metabolism. Liver dies --> can't produce urea --> NH3 builds up --> coma and death
206
Why do we need to store fuel from meals? What are three circumstances where we mobilise it?
The body cannot store ATP- it must be synthesised at the time and rate that it's needed, by oxidising stored fuels.
- between meals
- for immediate fuel for increased activity
- for long periods where food intake is inadequate
207
Name the main types (2) of fuel storage in the body, and their weights in a normal 70kg person.
Triacylglycerol- 15kg (equivalent to 590 000 kJ)
| Glycerol- 0.223kg
208
What gets stored as fat in the body?
Excess dietary fat and carbohydrate (and alcohol).
209
How can fatty acid chains differ?
By length, and by saturation (saturated or unsaturated).
210
Where do the components for stored TAGs come from?
Fatty acids- chylomicrons circulating in the blood
| Glycerol backbone- glucose circulating in the blood
211
How are fatty acids activated before they can be attached to the glycerol backbone to form a TAG? What stimulates this activation?
Fatty acid + acetyl-CoA --> fatty acyl CoA
| Insulin
212
Which kind of reaction occurs when fatty acyl-CoA is attached to the glycerol backbone to form a TAG? What stimulates it?
Esterification
| Insulin
213
Which enzyme releases fatty acids from the chylomicron? Where does this occur for fat storage? What stimulates this reaction?
Lipoprotein lipase
Capillaries of adipose tissue
Insulin
214
Describe the insulin receptor.
Insulin binds to alpha subunits on cell surface, which causes conformational change and cross-phosphorylation of internal subunits, which activates the tyrosine kinase to phosphorylate downstream targets in the cell.
215
Which enzyme catalyses the fatty acid --> fatty acyl CoA reaction, and where does the energy come from?
```
Fatty acyl CoA synthetase
ATP bonds (cleaved to AMP + PPi)
```
216
The glycerol in triacylglycerol originally comes from dietary glucose. How does glucose form glycerol?
The glucose molecule enters glycolysis. After the splitting reaction, DHAP undergoes a series of reactions to become glycerol.
217
Which enzyme mobilises fat stores in adipose for energy? What stimulates it? Where do the products go?
Hormone-sensitive lipase
Glucagon (hungry) and adrenaline (frightened, exercising)
- glycerol to the liver to be converted back into glucose
- fatty acids in fatty-acid albumin complexes to cells for beta-oxidation
218
Where is glycogen stored?
In granules in cytoplasm of liver and muscle cells.
219
Why is glycogen synthesised into a branched pattern?
It's optimal for maximum storage of glucose units in a small volume (~ 60 000 per molecule).
220
Which two enzymes are required for glycogen synthesis?
Glycogen synthase- 1,4 glycosidic linkages
| Branching enzyme- 1,6 glycosidic linkages
221
When and how does glucose diverge from glycolysis for glycogen synthesis?
After the hexokinase (first) reaction: glucose --> glucose-6-phosphate (using ATP --> ADP)
Mutase converts glucose-6-phosphate to glucose-1-phosphate, diverting from the glycolysis pathway.
222
What is the high-energy precursor of glycogen? Describe the reaction.
UDP-glucose
glucose-1-phosphate + UTP --> UDP-glucose + PPi
- catalysed by UDP-glucose pyrophosphorylase
223
What is the role of inorganic pyrophosphatase in glycogen formation?
Breaks PPi (diphosphate) into 2Pi, lowering the energy barrier so the reaction can't go backwards. Makes formation of UDP-glucose irreversible- needs a different enzyme to mobilise stored glycogen- carefully controlling storage vs. mobilisation.
224
Why can't excess glucose be converted into glycogen? What happens to it?
Glycogen is a large molecule- only so much space for it. Excess glucose --> acetyl-CoA --> fatty acids
- by the FA synthase complex in the liver cytosol
- exported as TAGs in VLDL- uptake by adipose cells stimulated by insulin
225
What happens to glucose mobilised by glycogenolysis in the liver, and in the brain?
Liver- released into the blood for the brain
| Muscle- released for glycolysis within muscle cells
226
What does the fatty acid synthase complex require, and which kind of fatty acids does it make?
```
NADPH
Palmitic acid (C16)
```
227
Which fuels do the brain, RBCs, liver, heart, and muscle use?
```
Brain- glucose
RBCs- glucose
Liver- mostly FAs
Heart- mostly FAs
Muscle- mostly FAs unless exercising- mix of FAs and glucose
```
228
How much glucose does the brain need per day?
120g
229
Which hormone stimulates processes for fuel supply during starvation? Name the processes (4).
```
Glucagon (because blood glucose drops)
Glycogenolysis
Gluconeogenesis
Ketogenesis
TAG mobilisation
```
230
How many days can we survive on TAG stores in adipose tissue? Why aren't TAG stores enough?
40 days of energy to our aerobic tissues except:
| Brain can't use fatty acids because they can't cross the blood-brain barrier.
231
TAGs are split into glycerol and FFAs when mobilised. How much glucose do we get from that glycerol per day?
~20g
232
Define glycogenolysis.
Mobilisation of glycogen (in liver and muscle) into glucose for energy.
233
How much glycogen is stored in the liver? How long can the brain survive on glucose from mobilisation of this glycogen?
90-120g
| One day
234
Name the steps of glycogenolysis (3).
1. glycogen + Pi --> glucose-1-phosphate
- glycogen phosphorylase
2. glucose-1-phosphate <=> glucose-6-phosphate
- mutase
3. glucose-6-phosphate + H2O --> glucose + Pi
- glucose-6-phosphatase
235
Which three substrates can be used for gluconeogenesis, and where are they sourced?
Lactate- muscle glycogen
Alanine- muscle proteins
Glycerol- TAGs
(all C3 backbones)
236
Where does the energy used for gluconeogenesis come from? In which two forms is this energy?
Fatty acid oxidation- fatty acids sourced from TAG mobilisation
ATP and NADH
237
Why do we need to avoid using body proteins for energy?
We have no protein stores, so we would be degrading proteins we need for functional processes in the body, which can cause damage.
238
Name two ketone bodies, and how they're synthesised.
Acetoacetate
Beta-hydroxybutyrate
Synthesised from acetyl-CoA from fatty acids in the liver (ketogenesis).
239
Why do we produce ketone bodies?
They can pass through the blood-brain barrier, where they're converted back to acetyl-CoA and used for energy. Slows down muscle degradation when starving because we don't need as much energy from amino acids for gluconeogenesis.
240
Define the two types of exercise.
```
Aerobic = low intensity, sustained period
Anaerobic = high intensity, shorter period
```
241
Name the ways ATP is generated in aerobic and anaerobic exercise.
Aerobic- glucose and fatty acid oxidation, requires O2
| Anaerobic- glycogen mobilisation and phosphocreatine dephosphorylation
242
How much phosphocreatine do we have per gram of muscle?
20 micromols
243
Which amino acids make up phosphocreatine?
Glycine and arginine
244
How does phosphocreatine produce ATP? Which enzyme is used?
Creatine kinase catalyses:
| Phosphocreatine + ADP <=> Creatine + ATP
245
What reaction does creatine kinase catalyse in recovering muscle fibres?
Creatine + ATP --> phosphocreatine + ADP
246
How many seconds of anaerobic exercise can be fuelled by ATP generation from phosphocreatine?
~10 s
247
How is muscle glycogen mobilised (2 reactions)?
1. glycogen --> glucose-1-phosphate by glycogen phosphorylase enzyme
2. glucose-1-phosphate --> glucose-6-phosphate by mutase
(G6P enters anaerobic glycolysis)
248
What is preventing glucose-6-phosphate in muscle being converted to glucose for use in the brain (like in liver glycogenolysis)? Why is this important?
Muscle cells don't have the phosphatase enzyme to remove the phosphate. So the G6P can continue down the glycolytic pathway to provide ATP for muscle cells.
249
Which hormone binds to muscle cell receptors to initiate glycogen mobilisation? Describe the signal transduction pathway. What other molecule stimulates this?
Adrenaline binds to beta-adregenic receptors.
- activates G-protein
- build up cyclic AMP
- activates kinases
- activates glycogen phosphorylase to convert glycogen --> glucose-1-phosphate
Ca2+ (also stimulates muscle contraction)
250
How is NAD+ regenerated during anaerobic glycolysis? How does this cause fatigue?
Pyruvate is reduced to lactate, NADH is oxidised to NAD+. Build up of lactate lowers muscle pH, causing fatigue.
251
How is glycolysis in exercising muscle regulated?
- adrenaline and Ca2+ stimulate it
| - AMP and inorganic phosphate are allosteric regulators of phosphofructokinase (increase its activity)
252
Describe the role of adenylate kinase in exercising muscle cells.
Converts 2ADP --> ATP + AMP
| ATP used for energy, and AMP increases (allosterically) phosphofructokinase activity
253
How does carnitine help generation of ATP? In which form of exercise is it helpful?
Allows fatty acid transport across the IMM into the matrix. Aerobic exercise- when fatty acid oxidation can take place.
254
How do type I muscle fibres differ to type II muscle fibres?
- more capillaries per fibre
- more myoglobin
- increased size and no. of mitochondria (more capacity to generate ATP via oxidative phosphorylation)
255
Name 7 symptoms of diabetes.
```
Intense thirst
Glucosuria
Hyperglycaemia
Ketones
Weight loss
Fatigue
Frequent urination
```
256
How do type I and II diabetes differ?
Type I is caused by lack of insulin from the auto-immune destruction of pancreatic beta cells. Treated with recombinant human insulin, <25 years old at onset.
Type II is caused by resistance to insulin as a result of lifestyle factors. Treated with change to lifestyle and hypoglycaemic drugs, >40 years old at onset.
257
What symptoms occur if blood glucose is too low (4)?
Sweating
Increased heartbeat
SNS may induce vomiting
Cognitive impairment because brain doesn't get glucose (aggressive mood, coma)
258
What happens if blood glucose is too high?
Proteins get glycated (non-enzymatic reaction)
- collagen in basement membranes of capillaries
- protein in the eye makes lens go opaque
Constriction of blood vessels --> gangrene, limb amputation
259
Describe insulin.
A peptide hormone synthesised in pancreatic beta cells. It's secreted in response to high blood glucose and acts on liver, muscle, and adipose cells.
260
What metabolic processes does insulin inhibit (5)?
```
Gluconeogenesis
Glycogenolysis
Proteolysis
Lipolysis
Ketogenesis
```
261
What metabolic processes does insulin activate (4)?
Uptake of glucose into muscle and adipose tissue
Glycogen synthesis
Protein synthesis
TAG uptake + fatty acid synthesis
262
How does blood glucose fall in type I diabetics with no insulin?
It's being used up by the brain, heart, and lungs.
263
Name the metabolic consequences of lack of insulin (7).
```
Impaired uptake of glucose in muscle and adipose cells (so decreased glycogen and muscle synthesis)
Increased proteolysis
Increased lipolysis
Increased glycogenolysis
Increased ketone body synthesis
Increased gluconeogenesis
Reduced removal of TAGs from the blood
```
The body starts to mimic starvation, because there is no fed signal.
264
How does decreased glucose uptake into tissues, and increased gluconeogenesis, lead to dehydration?
These cause hyperglycaemia and glycosuria. There is >10 mmol/L glucose in the kidney, causing osmotic diuresis (pulling water from tissue into the urine). This leads to electrolyte loss --> dehydration --> coma.
265
What effects do increased lipolysis and proteolysis have on the body?
Increased lipolysis --> excess fatty acids --> ketone bodies --> acidosis --> vomiting (contributes to dehydration)
Increased proteolysis --> muscle breakdown --> weight loss --> wasting and weakness
266
How do diabetic blood glucose levels when using injected insulin compare to normal levels?
About the same, but diabetic blood glucose still takes longer to decline.
267
Define obesity.
BMI > 30
| taking body composition into account
268
Which part of the obese state may contribute to insulin resistance?
Abnormal TAG storage in muscle and liver.
269
How much fat storage can we burn a day?
200g
270
Name the three components of metabolic rate.
BMR: obligatory energy expenditure
Physical activity
Adaptive thermogenesis
271
What regulates adaptive thermogenesis?
SNS
| Responds to temperature and diet
272
What occurs in the mitochondria of brown adipose tissue?
Uncoupling of respiration from oxidative phosphorylation
Proton gradient is dissipated by UCP uncoupling protein- regulated proton channel in IMM
Production of heat instead of ATP
273
What regulates the UCP uncoupling protein in brown adipose?
SNS/ noradrenaline
| Opens channel in cold, closes in warm temperature
274
Name three strategies we might use brown adipose tissue to combat obesity.
Stimulate existing BAT using drugs
Switch on brown fat differentiation from undifferentiated cells (pre-adipocytes and myoblast progenitor cells)
Transplantation of engineered BAT
275
How much of obesity is genetic?
Yes- 30-80% can be attributed to genes
276
Define leptin.
A hormone secreted from adipocytes which signals the brain to decrease food intake and increase energy expenditure. Maintains normal energy balance.
277
Which signal do most obese humans appear to be resistant to? Why?
Leptin
They are missing either a functional leptin receptor, or a different protein down the signalling pathway. (or multiple things)
278
Name three potential molecular targets for anti-obesity drugs.
Pancreatic lipase (blocked by Xenical)- absorb less fat
Leptin receptor- increase leptin levels
Mitochondria and brown fat- uncoupling oxidative phosphorylation from electron transport
