Cell Biology and Signalling Flashcards
1
Q
What are bacterial cell walls made from?
A
Peptidoglycan
2
Q
Which has an antagonist action to adenylate cyclase?
A
Phosphodiesterase
3
Q
Alpha helices and beta sheets are formed by which type of bonding?
A
Hydrogen
4
Q
What is Km a measure of and what does a lower value indicate?
A
Enzyme performance
Higher affinity
5
Q
Where does ATP production occur in:
a) Prokaryotes
b) Eukaryotes
A
a) Cell membrane
b) Mitochondria
6
Q
What three elements is the cytoskeleton made up of?
A
Actin
Microtubules
Intermediate filaments
7
Q
3 functions of SER?
A
N linked glycosylation
Detoxification of xenobiotics
Biosynthesis of membrane lipids + steroids
8
Q
Two functions of RER?
A
Proteins for secretion/ insertion go to cell membrane
Proteins folded, cys-cys bridge formed
9
Q
4 functions of Golgi apparatus?
A
Glycosylation of carbohydrates and lipids
Synthesise lysosomes
Synthesise + package material to be secreted
Direct proteins to correct compartments
10
Q
4 functions of peroxisomes?
A
Detoxification of toxins, alchol, FA
Phospholipid synthesis
Oxidation of VLCFA
Enzymes that synthesise and degrade H2O2
11
Q
What causes Zellweger syndrome?
A
Inherited absence of peroxisomes due to defects in targeting
12
Q
What causes adrenoleukodystrophy (ALD)?
A
Affects proteins that imports VLCFA into peroxisomes
13
Q
What is autophagy?
A
Organelle turnover/replacement
14
Q
Myoclonic epilepsy with Ragged Red Fibre (MERRF Syndrome)?
A
Mutation of mitochondrial gene for tRNA-lys
15
Q
Hutchinson - Gilford Progeria?
A
Mutation in lamin - A prt of nuclear envelope
Distorted shape of nucleus (blebbed)
Production of unique progerin protein
16
Q
Tay-Sachs disease?
A
Mutation of lysosomal hexosaminidase A enzyme
Causes accumulation of neurotoxic ganglioside
17
Q
What are operons (in bacteria)?
A
Functional units of DNA containing cluster of genes under control of a single promoter
18
Q
What are 6 types of enzymes and their functions
A
Oxidoreductases- catalyse transfer of hydrogen + electrons
Transferases - catalyze transfer of functional groups between molecules
Lyases - cleavage of C-C, C-O, C-N, addition to /formation of double bonds
Hydrolases - cleavage of bonds by addition of H2O
Isomerases - transfer of functional groups within same molecule
Ligases - catalyse formation of new covalent bonds using ATP, repair DNA breakage
19
Q
Soluble vs Membrane protein?
A
Soluble - in cytosol, hydrophobic core, hydrophilic surface
Membrane - embedded in membrane, hydrophobic surface
20
Q
What type of enzyme is chymotrypsin and what does it affect?
A
Hydrolase
Cleaves peptide bond on carboxyl side of tryptophan, tyrosine, phenylalanine and large hydrophobic residues e.g. methionine
21
Q
What makes up chymotrypsin catalytic triad?
A
Serine
Histidine
Arginine
22
Q
3 assumptions about Michaelis-Menton plot?
A
[S]»_space;[E]
[ES] x change with time (steady - state, made at same rate as broken down)
Initial velocities used, [product] small, back reaction of P to S ignored
23
Q
What is Michael - Menton equation?
A
V0= Vmax[S] /Km + [S]
24
Q
Equation for Km?
A
K2+ K-1/K1
25
Defintion of Kcat?
No. of substrate molecules converted to product in a given unit of time on a single enzyme molecule when enzyme saturated with substrate
26
Lineweaver- Burke Plot equation?
1/V0= Km/Vmax 1/[S] + 1/Vmax
| -1/Km is x-intercept, always -ve
27
How does a competitive inhibitor affect:
a) Michaelis-Menten plot?
b) Lineweaver-Burke plot?
a) Vmax same, Km increases and becomes Kapp (apparent)
| b) Kapp increases so x-axis intercept decreases (mehr -ve)
28
How does a non-competitive inhibitor affect:
a) Michaelis-Menten plot?
b) Lineweaver-Burke plot?
a) x affect Km but Vmax smaller
| b) Y-intercept increase, x-intercept same
29
What type of curve do allosteric enzymes show?
Sigmoid curve
30
Where are hydrogen bonds formed in alpha helix?
Between peptide bond carbonyl O and H of N-H every 4th peptide
31
How many residues per turn in an alpha helix?
3.6
32
How are the r groups in a beta pleated sheet arranged?
Trans position
33
What are the 2 types of beta pleated sheet and 1 feature of each?
Antiparallel - hairpin bend, widespread globular proteins
| Parallel - arrows point to C terminus
34
What is the AA change in sickle cell and why is it significant?
Glut ==> Val
| Hydrophillic to hydrophobic
35
What is phenylketonuria?
Defective phenylalanin hydroxylase (phe==>tyr)
36
What is main cause of albinism?
Defective tyrosinase (tyr ==> melanin)
37
What is molecular weight of water?
18g
38
What is Henderson-Hasselbach equation?
pH = pKa + log[A-]/[HA]
39
What is the physiological buffer in:
a) Saliva?
b) Blood?
c) Urine?
a) Bicarbonate
b) Haemoglobin
c) Phosphate
40
What are the common head groups found in glycophospholipids?
Choline, Serine, Ethanolamine, Inositol
41
What is characteristic of sphingomyelin?
No glycerol backbone, has single FA tail
42
What is significant about the arrangement of the positioning of the different glycophospholipids in the lipid bilayer?
Phosphotidylcholine and sphingomyelin face extracellular environment
Phosophotidylserine and phosphotidylethanolamine face cytosolic side
43
What is the equation for the hyperbolic curve of myoglobin?
Yo2 = Po2/P50 + PO2
44
What are the chains in adult haemoglobin and foetal haemoglobin?
Alpha 2, Beta 2
| Alpha 2, Gamma 2
45
What state does Hb have to be for BPG to be able to bind?
T state
46
What is BGP?
2-3-bisphosphate glycerate
47
Why is BGP induced stabilisation of T-state less efficient in Hbf?
Gamma chain has a H143S mutation, so it has a higher O2 affinity which is useful for the foetus
48
In what state does Hbs have to be so that aggregation is less likely to form?
R state (oxygenated)
49
What region of the Golgi apparatus faces:
a) ER?
b) Membrane?
a) Cis region
| b) Trans region
50
How are proteins targeted to mitochondria?
Complexed with chaperones
51
When proteins are targeted to the mitochondria, are they folded or unfolded?
Unfolded
52
How are proteins targeted to the nucleus?
Nuclear proteins contain nuclear localisation signal (NLS)
53
What does NLS bind to when
a) entering
b) leaving
nucleus via nuclear pore?
Importin and exportin
54
How are proteins targeted to lysosomes?
Lysosomal proteins are tagged with mannose 6-phosphate in the Golgi apparatus
55
What is inclusion cell disease?
The specific receptor that recognises mannose which targets vesicles to become lysosomes is faulty
56
What is mutant N-acetylglucosamine-1-phosphotransferase enzyme?
Doesn't tag proteins with mannose 6 phosphate so they don't reach lysosme
Lysosomes don't form
57
What are the size of actin microfilaments and and what are their polymers?
7-9 nm in diameter
| Actin
58
What are the size of intermediate filaments?
10nm
59
What are the size of microtubules and what are their polymers?
25nm
| Tubulin
60
What is the monomer of actin?
G actin
61
What is the orientation of g-actin when it polymerises to f-actin?
Head to tail orientation
Each microfilament has a + and - end
Monomers can be added to either end
62
4 functions of actin?
Muscle contraction
Mechanical support
Maintaining cell shape
Cell movement
63
What type of G actin binding protein is present in actin?
Thymosin beta 4 - inhibits polymerisation
64
What type of cross-linking proteins are present in actin?
Villin - parallel bundles in microvilli
| Filamen - joining at angles to create a mesh
65
What type of severing proteins are present in actin?
Gelsolin - cuts and binds to + end
66
What is cytokinesis?
Ring of actin forms in the centre of cells
Anchors to plasma membrane
Myosin contraction constricts cells
67
Examples of intermediate filaments in:
a) Epithelial cells?
b) Axons?
c) Universal (nuclei)?
a) Keratin
b) Neurofilamen
c) Lamins A, B, C
68
What is epidermolysin bullosa simplex?
Mutations in keratin resulting in skin blistering disease
69
What is amyotrophic later sclerosis (ALS)?
Abnormal expression of neurofilamens resulting in a neurodegenerative disease
70
What is a microtubule organising centre (MTOC)?
Core from which microfilaments grow out of
| Grow out until they reach destination then stabilized
71
5 functions of microtubules?
```
Dynamic scaffold
Movement of cargo to specific locations in cell
Central internal support of cilia
Stabilise structure of cells
Organise structure of organelles
```
72
What is the difference between kinetochore and aster microtubules?
Kinetochore attaches to centromere of chromatids
| Aster attaches centromere to cell membrane
73
What are the two motor proteins associated with microtubules?
Kinesin and Dynein
74
What direction to kinesin and dynein move towards?
Kinesin move towards + end, towards cell peripherary
| Dynein moves towards - end, near nucleus
75
What is the MTOC of cilia?
Basal body
76
What are the two types of cilia and where are they found?
Stereocilia - inner ear
| Motile cilia - lung
77
What is Situs Inversus?
Organs in mirrored position, caused by defect in cilia mediated movement of growth factors in embryo
78
What disease is caused by a mutated protein associated with abnormal function of primary cilia?
Autosomal dominate polycystic kidney disease
79
Where are these glc transporters found?
a) GLUT 1
b) GLUT 2
c) GLUT 3
d) GLUT 4
a) Ubiquitous
b) Liver, pancreatic beta cells
c) Neurones
d) Muscles, adipocytes
80
Which GLUT receptor is regulated by insulin?
GLUT 4
81
What does SGLUT transport?
Na and glc symport
82
What does phosphorylation of Na-K pump cause?
Conformational change that closes cytoplasmic access and opens external acess
Releases Na outside cell
83
What does hydrolysis of the phosphate group in the Na - K pump cause?
Opens cytoplasmic access and releases K into cell
84
The mutation in what protein causes cystic fibrosis?
Cystic fibrosis transmembrane conductance regulator protein
85
Five factors that act as extracellular signals?
```
AA and derivatives
Steroids
Prostaglandins - derived from arachidonic acid
Proteins and peptides
Gases
```
86
How does endocrine signalling work?
Signal produced by cells in one part of body and travels in blood to target cells elsewhere
87
How does autocrine signalling work?
Signal acts on same cell that produces it
88
How does paracrine signalling work?
Signal produced by cell acts on other cells that are very close
89
How does contact dependant signalling work?
Signal integral part of 1 cell and interacts directly with another cell
90
How does neuronal signalling work?
Electrical signal transmitted down cell + message passed to another via synapse
91
If hormone is hydrophilic, where is the receptor located?
Cell surface
92
If the hormone is hydrophobic, where is the receptor located?
Intracellular
93
What three domains does a steroid hormone contain?
Hormone binding domain
DNA binding domain
Domain for interacting with other transcription factors
94
How many transmembrane regions does GPCR have?
7
95
What does activation of the adenylyl cyclase produce?
Adenosine 3':5' cyclic monophosphate (cAMP)
96
What does activation of the phospholipase C produce?
Inositol 1,4,5 - triphosphate (IP3)
1,2-diacylglycerol (DAG)
Metabolises components of plasma membrane to become secondary messengers
97
Which part of the G protein complex dissociates when GTP binds?
Alpha subunit
98
How does the toxin produced by Vibrio cholerae cause the symptoms of cholera?
Enters epithelial cells + causes irreversible modification of Gs protein
Increased ion + H2O transport across gut wall into lumen
99
When RBC in liver are broken down in spleen and liver, what is haem broken to?
Bilirubin
100
What type of covalent bond is important for the subunit stability of proteins?
Sulfhydryl bridges between cysteine residues
101
A globular protein X found in blood can act as a buffer.
If the pKa of the protein is increased because of conformational changes in that protein how will the buffering/ hydrogen ion binding properties be affected?
Protein will bind more H+
102
At physiological pH which two amino acid residues are completely negatively charged?
a) Glu and Asp
b) Gln and Asp
c) Glu and Asn
d) Gln and Asn
e) Glx and Asp
Glu and Asp
103
How are secretory vesicles targeted to correct location in a cell?
V-snare protein on vesicle binds complementary t-snare protein in membrane
104
How is the lysosome created in a cell?
By vesicle targeting of Golgi body
105
Proteins are targeted to which organelle by the protein sequence Pro-Lys-Arg-Lys-Arg-Lys-Val?
Nucleus
106
The Na-Glc transporter is involved in what kind of transport?
a) Active transport
b) Secondary active transport
c) Simple passive transport
d) Gated ion transport
e) Facilitated diffusion
Secondary active transport
107
What are anchored proteins?
Proteins that are covalently linked to a fatty acid chain or to surface glycolipid
108
What are lipid rafts?
Ordered membrane microdomains linked to cell signalling that have high levels of cholesterol
109
What happens when EGF binds its specific receptor?
EGF receptor dimerizes and is auto-phosphorylated
110
What is the composition of microtubules?
Polymer of alpha-tubulin + beta tubulin heterodimers
111
What is the definition of the peptide bond?
Covalent linkage between amino acid residues that prevents rotation around C-N bond that results in R-groups being in trans arrangements
112
What is the sequence of molecular events that occurs when an agonist binds to its specific G-protein coupled receptor?
Conformation change in cytoplasmic domain of receptor
GTP binds to the G protein
G-alpha subunit dissociates
G-alpha subunit activates adenylate cyclase
cAMP created
cAMP activates Protein Kinase A
113
What subunits is PKA (protein kinase A) made up of?
Tetrameric enzyme
| 2 regulatory, 2 catalytic subunits
114
What part of PKA does cAMP bind to?
Regulatory subunits
| Catalytic monomers are now activated
115
What is CREB and what enzyme phosphorylates it?
cAMP Response Element Binding protein
| PKA
116
What enzyme does the Gq subunit activate and what reaction does is subsequently catalyse?
Phospholipase C
| Cleaves inositol phosphate in membrane (IP3 + DAG)
117
Which GLUT receptor is associated with levels of glc within cell being same as outside cells?
GLUT2
118
What are some examples of supersecondary structures?
Beta barrel
Beta sheet rolled
Beta sandwich
Rossmann fold
119
Which AA are.....
a) Positive?
b) Negative?
c) Uncharged polar?
d) Non polar?
a) E,D
b) H, K, R
c) S, N, Q, Y, T
d) A, G, V, L, I, P, F, M, C, W
120
What are 3 examples of non-coded AA?
Hydroxyproline - hydroxylation of proline, prt collagen
Selenocysteine - Contains Se, not S, encoded by subset of stop codons
Homocysteine - extra methyl group compared to C
121
Describe process of kinase cascade
```
EGF binds, autophosphorylates tyrosine in RTK (receptor tyrosine kinase)
GRB2 and Sos bind to receptor
GDP-Ras to GTP-Ras
Triggers kinase cascade
MapKKK to MAPKK to MAPK
MAPK activates transcription factor
```
122
Which is the only amino acid whose side chain contributes to buffering at physiological pH?
His
123
Amino acid side chains which are able to act as donors in forming hydrogen bonds include those which have what property?
Uncharged + polar
124
During what stage of the cell cycle do growth factors stimulate a cell to continue dividing?
G1
125
Kinase enzymes, such as glycogen synthase kinase, belong to which class of enzymes?
Transferases
126
In which type of reaction is FAD used as a cofactor?
Oxidation
127
Which cellular enzyme catalyses the production of the second messenger cyclic AMP (cAMP)?
Adenylate cyclase
