Receptor Mechanisms 2

Question 1

How long is G protein coupled receptor response?

Answer 1

Seconds or minutes

Slow

Question 2

Describe the structure of G protein coupled receptors?

Answer 2

One protein =>7 transmembrane domains
One agonist binding site in amino terminus
G protein interacts with C terminus with family of 3 GDP binding sites (a,B, y) => GDP only binds to large a-subunit
B+ y (gamma) are 2 anchors which holds it into membrane

Question 3

How are G protein activated?

Answer 3

G protein are signalling intermediates
Once receptor is activated, G protein split apart=> a subunit attach to enzyme to produce cellular response
When receptor is activated, a subunit undergoes conformational change so it has higher affinity for GTP
A subunit dissociates B +Y so leaves them behind in lipid phase
A subunit goes to interact with enzyme

Question 4

aGs stimulates ……..

Answer 4

Adenylate Cyclase

Increase in cAMP from ATP

Question 5

What does aGI do?

Answer 5

Inhibits adenylate cyclase

Decrease cAMP from ATP

Question 6

What enzyme does aGq/11 affect?

Answer 6

It stimulates phospholipase C

Produces 2 signalling molecule called DAG + IP3

Question 7

What happens in G protein termination?

Answer 7

Alpha subunit has an inherent GTPase
GTPase converts GTP-> GDP
GTPase => GTP bound to a-subunit is hydrolysed by a-subunit, asking phosphate group to be reduced
Now alpha GDP has poor affinity for enzyme so it goes back to beta +gamma subunits