CBS Flashcards
1
Q
Cells are the fundamental units of life meaning…
A
- All living organisms are made of cells.
- Higher organisms are ‘communities’ of cells.
- Individual cells perform specialized functions within ‘communities’.
- Nothing less than a cell can truly be called living e.g. viruses.
2
Q
Define the term cell.
A
A semi-independent, living unit within the body, (in unicellular organisms, completely independent) in which are found the mechanisms for metabolism, growth and replication (by division). It consists of an aqueous solution of organic molecules surrounded by a membrane.
3
Q
Define the term organelle.
A
A subunit within a cell, with a defined structure and performing specific, integrated activities. Some are bounded by membranes, others are non-membranous e.g. ribosomes.
4
Q
Define the term tissue.
A
An organised assembly of cells and their extracellular products which carry out similar and coordinated activities within the body (connective, lymphoid). An example is extracellular matrices.
5
Q
Define the term organ.
A
An assembly of tissues coordinated to perform specific functions within the body (eye, ear, heart, lungs, liver).
6
Q
Define the term system.
A
An assembly of organs with specific, related activities that share regulatory influences (e.g. respiratory) OR it may be a diffuse functional network of cells situated in many parts of the body, sharing specific activities (e.g. immune).
7
Q
Define the term prokaryote.
A
A single-celled organism in which the chromosome is a circular strand lying free in the cell (i.e. no nucleus) and has no membranous organelles e.g. Bacteria.
8
Q
Define the term eukaryote.
A
One or more cells in which chromosomes are enclosed in a nucleus. They typically have cytoplasmic, membrane-bound organelles, DNA divided into a series of linear chromosomes and considerable differences occur between cells within the same organism. All complex organisms (plants, fungi, animals, protozoa, algae) are eukaryotes.
9
Q
Define the term virus and explain how they infect cells.
A
An assemblage of nucleic acid (DNA or RNA) and proteins (and often other molecules) which is parasitic on prokaryotes/eukaryotes. Viruses invade cells, subvert their protein synthesis machinery to make more viruses instead of normal cell proteins, then escape to infect other cells. Viruses are not cells or organisms in the strict sense (they lack a plasma membrane and only operate chemically within host cells).
10
Q
What is the Cell Theory?
A
“All living things are made of cells and these arise through the division of pre-existing cells”.
11
Q
What is the difference between TEM and SEM and what is their main disadvantage?
A
TEM = electrons go through the specimen. SEM = electrons scatter off the cell surface.
Can only evaluate dead cells.
12
Q
What limits the maximum size of a cell?
A
Surface area and diffusion distance.
13
Q
Name three ways in which specialised cells have overcome the problem of size.
A
- Thin processes (cytoskeleton).
- Multi-nucleated cells.
- Gap junctions.
14
Q
What do organelles allow?
A
- Specialised environments to exist.
- Different functions to operate under different conditions.
15
Q
Describe two features of a nucleus.
A
- Largest organelle in cells (3-10μm).
- Only organelle clearly visible by light microscopy.
16
Q
What happens within the nucleolus?
A
- Where rDNA is transcribed.
- Where ribosome subunits are assembled.
17
Q
What are the functions of SER and RER?
A
SER:
- Biosynthesis of membrane lipids and steroids occurs.
- Start of N-linked glycosylation.
- Detoxification of xenobiotics (mainly liver cells) (e.g. P450 system) occurs.
RER:
- Is coated with ribosomes for translation, proteins for secretion or insertion into cell membrane.
- Proteins are folded; cys-cys bridges form.
- Vesicles are budded from RER and transported to the Golgi body.
18
Q
Describe the structure and function of the Golgi Complex.
A
The golgi is composed of 4-8 closely-stacked, membrane-bound channels (cisterna). They modify proteins delivered from RER via vesicles. They:
- Modify N-linked carbohydrates.
- Glycosylate O-linked carbohydrates and lipids.
- Synthesise/package materials to be secreted.
- Direct new proteins in vesicles to their correct compartments – acts as a sorting office.
- Transport membrane lipids around the cell.
- Create lysosomes.
19
Q
What are the functions of peroxisomes?
A
- Detoxification
- Phospholipid synthesis e.g. plasmalogens
- Oxidation of Very Long Chain Fatty Acids VLCFA
- Enzymes which generate (and degrade) H2O2
20
Q
Name two peroxisome pathologies.
A
- Zellweger Syndrome: the inherited absence of peroxisomes due to defects in targeting.
- Adrenoleukodystrophy (ALD): affects protein that imports VLCFA into peroxisomes.
21
Q
What are the functions of lysosomes?
A
- To produce >50 different hydrolytic enzymes that can hydrolyse all major cellular macromolecules.
- Involved in organelle turnover/replacement – autophagy.
22
Q
Name the dysfunctional organelles that cause:
- Hutchinson–Gilford Progeria Syndrome (HGPS)
- Myoclonic Epilepsy with Ragged Red Fibres (MERRF)
- Tay Sachs Disease
A
- Nucleus.
- Mitochondria.
- Lysosomes.
23
Q
What is a unique about prokaryotes and carbohydrates?
A
Prokaryotes use carbohydrates in their cell walls which is unique. This is important in antibiotic synthesis.
24
Q
What is glycosylation linked to?
A
Diabetes. One way to see how a diabetic is controlling their glucose levels is to look at the glycosylation of haemoglobin as this only happens when there is elevated glucose in the plasma.
25
What are aldoses and ketoses?
They are monosaccharides which contain one aldehyde group (aldose e.g. glucose) or one keto group (ketose e.g. fructose) which changes the functionality of the carbohydrate.
26
What causes the ring structure of sugars?
A nucleophilic attack by the lone pair of oxygen electrons of the hydroxyl group on the carbonyl carbon.
27
What is the difference between the α and β forms of sugars and why is this important?
The -OH group on the anomeric carbon is either down (α form) or up (β form).
This is important in polymerisation (formation of a glycosidic bond).
28
What makes a reducing sugar?
If the anomeric carbon is not attached to another molecule it is a reducing sugar.
29
What enzyme is needed to make a glycosidic bond?
Glycosyltransferase
30
What is the advantage of branched glycogen?
There are a large number of ends which means there are lots of sites where glycogen can be turned into glucose quickly.
31
Describe the digestion of glycogen in the diet.
1. Salivary α-amylase causes random hydrolysis of internal α(1→4) linkages.
2. Digestion is continued by pancreatic α-amylase to form a mixture of mono- and disaccharides.
3. Finally maltase produces glucose to be absorbed by the intestinal mucosal cells.
32
What are fatty acids?
Long chain aliphatic carboxylic acids that are metabolised via the β-oxidation pathway to generate ATP.
33
Which amino acids must we gain from our diet?
- Threonine
- Methionine
- Lysine
- Valine
- Leucine
- Isoleucine
- Histidine
- Phenylalanine
- Tryptophan
34
What are the single letter amino acid codes for tryptophan, glutamate, aspartate, lysine, glutamine and asparagine?
```
W : tryptophan
E : glutamate
D : aspartate
K : lysine
Q : glutamine
N : asparagine
```
35
What is phenylketonuria (PKU)?
Where you have defective phenylalanine hydroxylase (phe-tyr). Reduced levels of tyrosine lead to reduced dopamine and melanin production.
36
What are the features of a peptide bond?
It has a partial +ve charge on the O atom and a partial -ve charge on the N atom which allows peptides to form hydrogen bonds.
It is a rigid C-N bond with no rotation.
37
What amino acids are disulphide bridges between?
Cystines
38
Describe the four levels of protein structure.
1) Primary = a sequence of amino acids in a peptide chain.
2) Secondary = folding/coiling of a peptide chain (usually into a helix or beta sheet).
3) Tertiary = folded peptide chain folds upon itself.
4) Quaternary = folded peptide chains are joined together.
39
What amino acid will you never see in an alpha helix?
Proline
40
What is the backbone of an α-helix formed of?
Hydrogen bonds that form between the peptide bond carbonyl-O & H of N-H every 4th peptide.
41
What holds β-pleated sheet strands together?
Hydrogen bonding between the peptide chains.
42
What are the two types of β-pleated sheet?
Antiparallel and parallel.
43
What is the difference between a collagen triple helix and an α-helix?
- Collagen triple helix has a left-handed turns and contains large amounts of proline and hydroy-proline.
- α-helices are right-handed and you will never see proline in their structure.
44
What features do proteins with high % of β-pleated sheet have?
They have a high tensile strength but no elasticity. They include fibrillar proteins (silk fibres) and are not very common.
45
What does the word domain mean to a structural biologist?
A particular unit of structure that is common. Also known as supersecondary structures.
46
Which amino acids have residues that are charged at physiological pH?
- Aspartate and Glutamate have ionised carboxyl groups.
| - Lysine and arginine have ionised nitrate groups.
47
What are Van der Waals forces?
The sum of the attractive or repulsive forces between molecules excluding those due to covalent bonds, hydrogen bonds or electrostatic forces.
48
What happens when proteins get too close to each other?
The Van der Waal's forces cause positive nuclei to repel each other ensuring the correct distance is maintained.
49
Name three diseases that are caused by misfolding of proteins.
- Sickle cell disease caused by polymerisation of HbS.
- Amyloid proteins forming plaques in Alzheimer's disease.
- Prion protein polymerisation in Creutzfeldt-Jakob disease.
50
Define an enzyme.
Biological catalysts which speed up the rate of a reaction without altering the final equilibrium between reactants and products.
51
What is the effect of an enzyme on activation energy of a reaction?
An enzyme lowers the transition state (free energy of activation) allowing a reaction to happen faster.
52
What is an intermediate in a reaction?
Something that may be happening during the process of A going to B. It is of high energy so is not very stable, but can be chemically isolated.
53
What are the six major classes of enzymes?
1) Oxidoreductases - add O2 or remove 2H
2) Transferases - transfers functional groups from donors to acceptors
3) Hydrolases - hydrolytic reactions (cleaving bonds by adding water)
4) Lyases - adding groups to C=C bonds and cleaving C-C, C-O or C-N bonds
5) Isomerases - transfer of functional groups between like molecules
6) Ligases - forms C-C or C-N bonds with ATP
54
What are homo- and hetero-oligomers?
- Homo = the same chain repeated many times.
| - Hetero = a structure formed of multiple chains.
55
What is the chymotrypsin mechanism?
Phase 1:
- The enzyme creates nucleophile from serine side-chain.
- The nucleophile attacks the substrate.
- Covalent intermediate is formed with second product (PN) bonded to serine and first product (PC) is released.
Phase 2:
- The enzyme creates a nucleophile from a water molecule.
- Nucleophile attacks the covalent intermediate breaking the covalent bond to serine.
- The second product (PN) is released.
56
What are isoenzymes?
Enzymes with different protein structures which catalyse the same reaction. They are coded by different genes.
57
What is enzyme kinetics?
The study of the rate of an enzyme catalysed reaction and how the rate varies with different substrate concentrations, amounts of inhibitors, metal ions and cofactors as well as pH.
58
What is reaction rate?
Either: decrease in the amount of substrate per unit time
Or: increase in the amount of product formed per unit time.
59
What is the Michaelis-Menton reaction model used for?
It allows you to understand and quantify the velocity as a function of the substrate concentration using the individual kinetic equations.
60
What are the three assumptions for the Michaelis-Menton reaction model?
1) Any amount of substrate bound by the enzyme at one time is small.
2) The enzyme-substrate complex does not change with time.
3) Initial velocities used and concentration of product can be ignored.
61
What is the Michaelis-Menton equation?
V0 = Vmax x [S] / Km + [S]
Where:
- V0 = initial reaction velocity, measured as soon as the enzyme and substrate are mixed.
- Vmax = maximal velocity of an enzyme catalysed reaction (when all enzyme active sites are fully saturated).
- Km = Michaelis constant
- [S] = substrate concentration.
62
What happens when you plot V0?
You get a hyperbolic curve.
63
What does Km equal?
Half of Vmax
64
What does the value of Km mean in terms of affinity?
The lower the value of Km, the higher the affinity of a substrate for a particular enzyme.
65
What is Kcat?
The turnover number i.e. the number equivalent to the number of substrate molecules converted to product in a given unit of time on a single enzyme molecule when the enzyme is saturated with substrate. This tells you how efficient the enzyme is.
66
What is the best method for comparing catalytic efficiency?
A Kcat/Km ratio. A high ratio shows that the enzyme is extremely efficient.
67
What is the Lineweaver-Burke plot and what is it used for?
Where you rearrange the Michealis-Menton plot to form the equation for a straight line.
This can be used to determine Km and Vmax as well as to determine the action of enzyme inhibitors (if they are competitive or non-competitive).
68
Why is finding -1/Km extrapolation?
Extrapolation is when you have a limited set of experimental values and you're looking at the value that the best fitting shows you - you're following the line of best fit to a value that doesn't exist. This applies to -1/Km because it is impossible to have a negative substrate concentration.
69
What are the differences between lactate dehydrogenase in the heart and the muscle?
- Muscle has a high Kcat because muscle generates a large amount of lactate during exercise.
- Heart has a lower Kcat because if levels of lactate in the heart are as high as the muscle, you're probably dead. Instead, it has a low Km allowing for small amounts of lactate to be removed quickly.
70
What is a new test developed by KCL used to detect a heart attack in A&E?
Blood test for the levels of cardiac myosin-binding protein C (cMyC). Levels increase in the blood during a heart attack.
This method is more efficient than the troponin method currently used.
71
What is the effect of a competitive inhibitor on Km and Vmax?
- Km increases.
- Vmax is not affected due to theoretical conditions of an infinite substrate concentration.
The curve shifts to the right.
72
What is the effect of a non-competitive inhibitor on Km and Vmax?
- Km stays the same.
| - Vmax is lowered considerably.
73
What are allosteric binding sites?
They are binding sites that are different from the active site and provide a level of regulation. Effectors or inhibitors can bind here.
74
What is a hallmark of allosteric modification of enzyme activity?
A sigmoidal curve of substrate concentration.
Haemoglobin is an example of this.
75
State the typical effector, change and time required for change for the following regulator events: 1) Substrate availability; 2) Product inhibition; 3) Allosteric control; 4) Covalent modification; 5) synthesis or degradation.
See table slide 47 in Enzyme Kinetics lecture.
76
What is pH?
A measure of hydrogen ion concentration i.e. the acidity or alkalinity of a solution. pH is the -log of the hydrogen concentration in a solution.
77
What is the normal pH range of blood?
7.35-7.45
78
What is the living range of blood pH?
7-7.8
79
How do acids enter our body?
- In foods we eat
- The breakdown of proteins
- The incomplete oxidation of fats or glucose
- Loading and transport of CO2 in the blood
80
What regulates the acid-base balance in the body?
- Lungs
- Kidneys
- Chemical buffers
81
How do the lungs reduce the acidity of the blood?
By increasing the rate of breathing to expel more CO2, as long as the acidosis is not too severe.
82
How do buffers resist abrupt and large swings in pH of body fluids?
- Releasing H and acting as acids when the pH begins to rise.
- Binding H and acting as bases when the pH drops.
83
Give an example of a a) strong acid; b) strong base; c) weak acid; d) weak base.
a) HCl
b) NaOH
c) Ethanoic acid
d) Ammonia
84
What is the body water %age of a) infants; b) elderly; c) healthy young man and d) healthy young woman?
a) 73% (low body fat and bone mass)
b) 45%
c) 60%
d) 50% (more fat)
85
What is the ionic product of water in any aqueous solution?
[H+] x [OH-] = 10^-14 M^2
At neutrality -> [H+] =[OH-] = 10-7M
86
What is the hydrogen ion concentration when the pH is 2?
[H+] = 10^-2 M
87
What is the OH- concentration if the H+ concentration is 10^-2?
10^-12
Both numbers add up to 14 - the scale of pH.
88
What are proton donors and what are proton acceptors?
- Donors = acids
| - Acceptors = bases
89
What is pKa?
The point where you have 50% of the acid form and 50% of the base form of an acid.
90
What is the equivalence point?
The end point where all of the acid is base (titration has finished).
91
How can you tell if an acid is a good physiological buffer?
If the pKa value is within the physiological pH range then it is good.
92
How does the pKa value change in acids with more than one hydrogen to give away?
Each pKa value is the midpoint between each acid form.
For example phosphoric acid has three hydrogens so it has three midpoints.
H3PO4 -> H2PO4-
H2PO4- -> HPO4^2-
HPO4^2- -> PO4^3-
93
What is Ka?
The dissociation constant i.e. the pH at which half of the acid has dissociated.
94
How do you calculate pKa?
pKa = -logKa
95
Why is pKa important?
Because if a substance has a pKa, it is able to act as a buffer.
96
What does low pKa indicate?
That it is a strong acid.
97
What is the Henderson-Hasselbalch equation?
pH = pKa + log([conjugate base (A-)])/([acid (HA)])
98
What does low pH mean in terms of A- and HA?
Low pH = low A- and high HA.
99
What causes respiratory acidosis?
High CO2
100
What causes metabolic acidosis?
Low bicarbonate
101
At what point is the buffering ability of a substance at its best?
Its pKa value.
102
What are two physiologically important buffers in humans?
- Carbonic acid (pKa 6.1)
| - Phosphoric acid (pKa 6.8)
103
What is the only good amino acid physiological buffer?
Histidine
104
Why is deoxyhaemoglobin a better buffer than oxyhaemoglobin?
Histidine is present in haemoglobin which is capable of acting as a buffer. When oxyhaemoglobin loses an O2 it undergoes a conformational change. This means the histidine goes to a different place so can accept hydrogen more easily.
This means that deoxyhaemoglobin (pKa 7.8) is a better buffer than oxyhaemoglobin (pKa is 6.8) so compared to blood, it is more acidic. This means that is won’t accept as many hydrogens as its equivalent.
105
What types of lipids are used for a) energy storage, b) precursors to vitamins and hormones and c) bile acids?
a) Triacylglycerol
b) Steroids
c) Cholic acid
106
What are phospholipids composed of?
A polar head group (serine (amino acid), choline (amino group), ethanolamine or inositol (carbohydrate)) which is attached to a back bone (glycerol) through a phosphate group. Two fatty acid side chains are linked to the glycerol backbone via ester bonds.
107
What does amphipapthic mean?
Where a molecule has both hydrophilic and hydrophobic parts.
108
What is sphingomyelin?
A type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath that surrounds nerve cell axons.
109
Where is ceramide found?
It is a component of sphingomyelin found in neurological tissue.
110
What type of fatty acids are found in membranes?
Fully saturated (no double bonds).
111
What is plasma membrane fluidity?
The ease with which lipid molecules move about in the plane of the bilayer. This is important in the regulation of membrane function.
The lipid composition of a membrane defines its fluidity.
112
What is flip-flopping?
This occurs in membranes where an internal lipid moves to the external side. This is not a favourable movement because it must move through a hydrophobic environment. Enzymes can facilitate this movement.
113
What factors membrane increase fluidity?
- Short chain fatty acids
| - Unsaturated fatty acids
114
What decreases membrane fluidity?
High cholesterol
115
How does decreased fluidity affect red blood cells?
The decreased fluidity causes cell shape to change, O2 transport is changed and the cells are destroyed leading to anaemia.
116
How are anchored membrane proteins attached to the lipid bilayer?
They are covalently linked to fatty acid chains or on the cell surface to glycolipids.
117
How are peripheral membrane proteins attached to the lipid bilayer?
By interactions with other membrane proteins or with the polar head group of phospholipids.
118
What does high salt/urea remove from the plasma membrane?
Peripheral membrane proteins.
119
What does detergent remove from the plasma membrane?
All proteins.
120
What do phospholipases remove from the plasma membrane?
Anchored proteins and some peripheral proteins.
121
What can be used as a delivery agent for gene therapy?
A synthetic bilayer/micelle which is capable of placing proteins in plasma membranes or inside cells.
122
What is haemoglobin?
A tetrameric heme protein found in erythrocytes (RBCs).
123
What is myoglobin?
A monomeric heme protein found mainly in muscle tissue. Its major physiological role is to facilitate oxygen transport in rapidly respiring muscle. It receives O2 from haemoglobin.
124
Why does haemoglobin follow a sigmoid curve?
Because when oxygen binds, it causes Hb to undergo a conformational change which affects the binding of more O2.
125
What is the Bohr effect in reference to haemoglobin?
An increase in pH and decrease in CO2 concentration increases haemoglobin's affinity for O2.
126
What is BPG?
It is a substance that lowers the affinity for O2 compared to pure haemoglobin.
127
What do high levels of BPG indicate?
High levels of BPG indicates high rates of metabolism in tissues indicating they need more O2 leading to a lower affinity for O2 in haemoglobin causing O2 to leave haemoglobin and enter tissues and helps haemoglobin take up CO2.
128
By what age does all trace of HbF disappear?
6 months
129
What happens when oxygen binds to haemoglobin?
- Fe ion movement is induced towards the heme plane.
- Movement of the F helix is induced.
- Facilitates the allosteric transition from the T state (tense) to the R state (relaxed).
130
Aside from O2, what else does haemoglobin transport?
- 15-20% of CO2 produced.
| - 40% of H+ produced.
131
What happens to CO2 when it binds to haemoglobin?
It reacts with the N-termini on haemoglobin to produce carbamino terminal residues.
132
What do the pKa values of oxy- and deoxyhaemoglobin tell us about O2 binding?
Oxy haemoglobin has a pKa of 6.6, deoxy = 7.8. Deoxy is higher than oxy meaning that when you consider the physiological pH of blood (7.4) oxy haemoglobin is completely ionised. Therefore, the only one that is able to bind protons is deoxyhaemoglobin.
133
How does BPG bind to haemoglobin?
It binds to the pocket in the centre of the haemoglobin tetramer, but only in the T (tense, deoxy) state. This stabilises the molecule and drives more R state haemoglobin to T state causing more O2 to be released.
134
Why does BPG have a less efficient effect on HbF compared to HbA?
Because the γ chain in HbF has a sequence variation affecting binding of BPG.
135
What happens to sickle cell anaemia haemoglobin when it becomes deoxygenated?
The conformation is altered dramatically causing it to aggregate into insoluble fibres. These fibres deform the RBCs into spiny or sickle-shaped cells.
136
What are porphyria diseases?
Where the body is unable to produce enough haem leading to a build-up of porphyrins in the body.
137
What is thalassemia?
A disease caused by faulty haemoglobin synthesis.
138
What can be used to indicate the past dietary history of a diabetic patient?
The levels of HbA1C in the blood. These are glycosylated haemoglobin that are due to high levels of glucose in the blood.
139
What are the two methods of protein targeting?
1) Proteins targeted via the ER then packaged into vesicles.
2) Translated in the cytosol and then trafficked to other parts of the cell.
140
What is a signal sequence?
A sequence found within the primary protein sequence that is used as a signal to direct the protein through a particular pathway in a cell.
141
How are proteins synthesised at the ER?
- Protein synthesis is initiated in the ribosome in the cytosol.
- A signal recognition particle (SRP) recognises and binds to the signal sequence of the protein as it emerges from the ribosome.
- SRP then binds to a receptor on the ER when it is still bound to the protein and then displaces.
- The protein is then directed through a translocon channel in the ER membrane.
- The signal sequence is then cleaved via signal peptidase and SRP is recycled.
142
What happens when proteins that are synthesised are destined to stay in the ER membrane?
They contain a hydrophobic stop sequence of 20-22 amino acids in length that remains as the transmembrane segment of the protein.
143
How are proteins transported in the ER?
Via membrane vesicles.
144
What happens to proteins when they leave the ER?
They travel to the cis region of the golgi via vesicles. By this point they are completely folded and synthesised.
145
What are V and T snares?
```
V-SNARE = vesicle
T-SNARE = target
```
These snares define where vesicles end up e.g. for plasma membranes, their v-SNAREs will bind with t-SNAREs on the plasma membrane and they will fuse.
146
What happens to proteins that are destined to go to the mitochondria?
The targeting happens after translocation is completed but before complete protein folding occurs. The proteins are complexed with HSP70.
147
How are proteins transported into the mitochondria?
A signal sequence is recognised by a cell-surface protein on the mitochondria causing the precursor protein to cross the mitochondrial membrane through protein translocator contact sites with the use of ATP.
This happens twice because you have two membranes.
When the protein reaches the mitochondrial matrix, the signal sequence is cleaved forming the mature protein.
148
How are proteins targeted to the nucleus?
- Proteins are translated and folded in the cytoplasm.
- Nuclear proteins contain nuclear localisation signal (NLS) which binds to importin and is transported through the nuclear pore.
149
What does nuclear protein targeting require?
G-protein Ran and hydrolysis of GTP.
150
What exports proteins from the nucleus?
Exportin
151
How are proteins targeted to the lysosome?
Lysosomal proteins are tagged with mannose-6-phosphate in the golgi. The proteins are then directed into transport vesicles which will become the lysosme.
152
What is inclusion cell (I cell) disease?
Where proteins are not tagged with mannose-6-phosphate in the golgi so do not reach the lysosome.
This causes developmental defects as cells are unable to break down things.
153
What are the three filaments that make up the cytoskeleton?
From large to small:
1) Actin (microfilaments, F-actin)
2) Intermediate filaments
3) Microtubules (made of microtubule associated proteins (MAPs))
154
What are the individual actin proteins that make a microfilament called?
Globular actin (G-actin)
155
How many actin subunits make a complete turn in a double helix?
13
156
What is required for the growth of actin molecules?
ATP bound to the G-actin monomer
157
How do actin filaments create movement?
By joining globular units at one end and losing them at the other.
158
What are the three major functions of actin?
1) Mechanical support
2) Cell shape changes and maintenance
3) Cell motility
159
What are intermediate filaments made up of?
They are polymers of individual intermediate filament proteins.
160
Where would you find the most dense network of intermediate filaments?
Around the nucleus (used to support nuclear structure).
161
What are the functions of intermediate filaments?
- Supports organelles by creating a meshwork in cells.
| - Used to anchor cells at some cell junctions.
162
What happens to mice that lack neuroflamins?
They have a reduced axon diameter leading to drastic consequences.
163
How are intermediate filament polymers formed?
1) Two intermediate filament proteins form a helical dimer.
2) Two dimers combine to form a tetramer (the fundamental unit of intermediate filaments).
3) Tetramers link in a staggered formation and end-to-end to form the final filament polymer.
164
What does the bundled structure of intermediate filaments mean?
They are more static, rope-like and stronger than actin filaments.
165
What links intermediate filaments to actin and microtubules?
Plectin
166
What are the unique characteristics microtubules?
- Can be rapidly disassembled and reassembled (called a catastrophe).
- They are very rigid because they are hollow tubes.
167
What subunits make up microtubules?
Tubulin alpha and beta. The two together create polarity.
168
What causes microtubule subunits to bind and dissociate?
When bound to GTP they bind to the plus end of the tubule. Over the GTP loses its Pi and goes to GDP causing the monomer to be lose from the negative end.
169
What role does actin have in polarised epithelia?
Helps form an adhesion belt that helps polarise cells in order to form orientation.
170
What are stereocilia?
They are actin structure found in the inner ear that when sound waves come, are pushed together connecting ion channels which triggers an AP.
171
What are the roles of microtubules in platelets?
Platelets grow microtubules very quickly as a part of the immune response allowing them to clump together forming a blood clot.
172
What filaments are responsible for stabilising axons?
Intermediate filaments and microtubules.
173
What filament is the ER dependent on?
Microtubules are essential for keeping the ER intact.
174
What filament is required to hold synaptic vesicles close to the presynaptic membrane?
Actin is released when the nerve signal has been stimulated.
175
How does actin-based cell movement occur?
1) The cell pushes out protrusions at the leading edge. Actin filaments polymerise providing the force for membrane protrusion.
2) The protrusion adheres to the surface the cell is moving across through focal contact junctions. F-actin connects to the focal adhesions to provide the contractile force.
3) Motor proteins pull the rest of the cell towards its destination and actin depolymerises at the rear leaving cytoplasmic residues behind which are later removed as they lose their adhesion.
176
What are lamelliopodia?
Exploratory and motile projection of a cell containing actin filaments. Polymerisation of actin at the ends pushes them out.
177
What happens when lamellioipodia reach a surface?
They attach to the extracellular matrix of the surface through the formation of focal adhesions (integrins). The actin filaments then connect the focal adhesions to the rest of the cytoskeleton of the cell.
178
How are microtubules arranged in cilia?
9 double-microtubule tubes in the periphery and two individual tubes in the centre form a cilia.
179
What mediates movement in cilia and how?
Dynein.
It is attached to the basal lamina and when it moves, it climbs up its microtubule. Because it is fixed at one end, the only thing that can happen is bending.
180
What are the two motor proteins that move intracellular contents and organelles inside cells?
- Kinesin moves towards + ends (cell periphery)
- Dynein moves towards – ends (near nucleus).
They walk along microtubules and are always attached i.e. progressive motor proteins.
181
What are the effects of colchicine, vinblastine and taxol?
They are anti-cancer drugs that inhibit the function of mitotic spindles and therefore cell division.
182
What do listeria bacteria do to encourage spread of infection?
When they are engulfed by the host cell, they escape from the phacocytic vesicle and have f-actin polymerised at the back of the bacterium providing motility which drives the bacteria into neighbouring cells.
183
What does the rate of diffusion depend on?
The partition coefficient (Kow) which is the equilibrium constant for partitioning of a molecule between oil (octanol) and water (how long it takes for the two to separate after mixing).
184
What does a high Kow value mean?
The more lipid soluble a substance is.
185
Define uniport, symport and antiport.
Uniport = Single molecule moving one way through a channel.
Symport = Two molecules moving one way through a channel.
Antiport = Two molecules moving in opposite directions through a channel.
186
Where are GLUT1, 2, 3 and 4 found?
1 = abundant in erythrocytes and BBB.
2 = liver, pancreatic beta cells.
3 = neurons.
4 = muscle, adipocytes (regulated by insulin).
187
Describe the glucose affinities for the GLUT transporters.
GLUT1 = High affinity for glucose (low Km).
GLUT2 = Low affinity (high Km) but high capacity so is capable of transporting glucose when levels are very high in order to regulate levels.
GLUT3 = High affinity (low Km).
GLUT4 = Km is similar to the upper range of blood glucose concentrations. Activity is mainly regulated by insulin.
188
How does GLUT5 differ to other GLUT transporters?
It is a fructose transporter.
189
How does insulin regulate GLUT4?
When insulin binds to a membrane transporter, a phosphorylation cascade is triggered which causes GLUT4 to be expressed on the plasma membrane. GLUT4 is recycled and removed from the membrane when insulin levels fall.
190
In which disease is the Na/K ATPase a drug target? How?
Congestive heart failure.
Ouabain blocks the channel by preventing K binding which causing an increase in intracellular Na. This inhibits the Na/Ca antiporter which causes an increase in intracellular Ca which hopefully will trigger cardiac muscle contraction.
191
What is a secondary active transporter? Give example.
A transporter that utilises an electrochemical gradient that has been set up by an active transporter.
E.g. SGLUT1 which transports glucose absorbed from the lumen of the gut to the bloodstream and is found in the epithelia of proximal tubules for reabsorption of glucose.
192
Define endocrine, autocrine and paracrine.
Endocrine = signal produced by cells in one part of the body travels in the blood to target cells elsewhere.
Autocrine = signals act on the same cells that produce it.
Paracrine = signal produced by cells act on other cells in close proximity.
193
What are the four types of cell signalling?
1) Depolarisation of cell membrane due to flow of ions.
2) Direct activation of transcription factors.
3) Generation of secondary messengers inside cells (c-AMP).
4) Direct activation of enzymatic kinase activity.
194
What are the three amino acids that are phosphorylated in cells?
Serine
Threonine
Tyrosine
E.g. serine -> phosphoserine
195
How do steriod hormones directly activate transcription factors?
Steriod hormones contain a hormone binding domain, a DNA binding domain and a domain for interaction with other transcription factors.
When they bind to their intracellular receptor, they form dimers with another bound steroid which induces a conformational change allowing binding to DNA and activation of transcription of target genes.
196
What happens when adenylyl cyclase is activated?
cAMP is produced
197
What happens when phospholipase C is activated?
IP3 and DAG is produced from the cleavage of inositol phospholipids.
198
What are cAMP, IP3 and DAG and what triggers their production?
They are second messengers triggered by binding of G-protein coupled receptors.
199
What happens when G-proteins are activated?
The alpha subunit (bound to GDP) becomes phosphorylated to GTP and dissociates from the complex and activates the effector enzymes (e.g. adenylyl cyclase).
200
What are examples of effector enzymes?
Adenylyl cyclase
| Phospholipase C
201
How does cAMP activate PKA?
PKA consists of two regulatory and two catalytic proteins.
cAMP binds to the regulatory subunits freeing the catalytic ones which then go and phosphorylate proteins.
202
How does cAMP affect gene transcription? When is this seen?
PKA (activated by cAMP) phosphorylates CREB (cAMP response element binding protein) which then binds to specific sequences in target genes to stimulate transcription.
This is a long-term adaptation to starvation.
203
What activates phospholipase C?
α1-adrenergic receptors bind to adrenaline causing the Gq subunits from g-protein coupled receptors to dissociate activating phospholipase C.
204
What are the effects of IP3 and DAG on the cell?
IP3 = activates Ca channels in the ER to increase Ca concentration in the cytosol.
DAG = works with Ca to activate protein kinase C.
205
What activates adenylyl cyclase?
β-adrenergic receptors bind to adrenaline causing the Gs subunits from g-protein coupled receptors to dissociate activating adenylyl cyclase.
206
What happens when epidermal growth factor (EGF) binds to receptor tyrosine kinase (RTK)?
It causes autophosphorylation of tyrosine residues in the cytoplasmic domain of RTK.
Adaptor proteins Grb2 bound to Sos binds to RTK via the SH2 domain. Sos is bound to a molecule called RAS which is phosphorylated to GTP-RAS from GDP-RAS.
207
What happens when GTP-RAS is created?
1) GTP-RAS is activated RAS which activates RAF kinase.
2) RAF kinase posphorylates and activates MEK1&2.
3) MEK1&2 phosphorylates and activates mitogen-activated protein kinase (MAPK).
4) MAPK then goes on to phosphorylate many other targets including transcription factors.
