G protein coupled receptors

Question 1

3 superfamilies of cell surface receptor

Answer 1

G protein coupled (mAchR)
Ligand gated ion channels (nAchR)
Receptors with intrinsic enzyme activity (tyrosine kinase)

Question 2

Ligands acting at adrenoreceptors

Answer 2

Endogenous: Noradrenaline/adrenaline
Exogenous: Isoprenaline, Salbutamol, Propranolol

Question 3

G protein coupled receptor uses for treatment

Answer 3

Anti asthma (B2 adrenoreceptor agonists)
Analgesia (opoid receptor agonists)

Hypertension (B2 adrenoreceptor antagonist)
Antischizophrenic (D2 dopamine receptor antagonists)

Question 4

Therapeutic drug uses

Answer 4

Agonists (activate)

Antagonists (dont activate)

Question 5

GPCR structure

Answer 5

Single polypeptide chain
7 transmembrane spanning domains
Extracellular N terminal
Intracellular C terminal

Question 6

What do G protein coupled receptors respond to?

Answer 6

Variety of stimuli
sensory GPCRS sense light, odours and tastes
Ions
Neurotransmitters (ach)
Peptide/nonpeptide hormones
Large glycoproteins

Question 7

2 binding regions in GPCR

Answer 7

within Transmembrane domains (within membrane)

N terminal region (extracellular)

Question 8

What happens to GPCR when ligand binds?

Answer 8

Conformational change

Question 9

What does activated GPCR facilitate?

Answer 9

Activation of G proteins that are inside cell

Question 10

G protein stands for?

Answer 10

Guanine nucleotide binding site

Question 11

How do GPCRs cause change?

Answer 11

Interact with G protein

GDP is exchanged for GTP

Question 12

G protein structure

Answer 12

3 subunits (alpha, beta, gamma)

heterotrimeric

Question 13

How is G protein activated?

Answer 13

GDP is swapped for GTP
alpha subunit splits off from beta-gamma
These can then interact with effector proteins

Question 14

How is G protein signalling stopped?

Answer 14

GTPase hydrolyses GTP to GDP
Alpha, beta-gamma subunits come back together
= inactive

Question 15

What governs G protein receptor selection by GPCR?

Answer 15

Galpha subunit

Question 16

How is specificity in response maintained by G proteins?

Answer 16

alpha and beta-gamma subunits interact with specific effector proteins

Question 17

G protein types

Answer 17

Gas - Stimulates adenylyl cyclase
Gai - inhibits adenylyl cyclase
Gaq - stimulates phospholipase C

Question 18

B adrenoreceptor G protein

Answer 18

Gas

Question 19

a2 adrenoreceptor G protein

Answer 19

Gai

Question 20

a1 adrenoreceptor G protein

Answer 20

Gaq

Question 21

Examples of things that interfere with G proteins

Answer 21

Cholera and Pertussis

Toxin binds to cell and injects enzyme in

Question 22

Effects of cholera

Answer 22

Covalently modifies Gas subunit
Removes GTPase
G protein cannot be inactivated (ON)
= increase in cAMP (opens water channels)
= diarrhoea and dehydration

Question 23

Effects of Pertussis

Answer 23

Covalently modifies Gai protein
Cannot exchange GDP for GTP
No effectors (frozen) OFF