G protein linked

Question 1

structure of a G protein coupled receptor

Answer 1

they are 7 transmembrane receptors so have 7 transmembrane helices

Question 2

what is the difference between the first and secondary messenger

Answer 2

first messenger is the ligand that binds the receptor

secondary messenger is the molecule produced inside the cell in response to the activation of the ligand

Question 3

structure of a G protein

Answer 3

3 domains, alpha beta gamma
beta and gamma domains never separate
alpha subunit can bind GTP/GDP and dissociate from beta/gamma domains

Question 4

steps of G protein activation cycle

Answer 4

1. hormone binds to G protein coupled receptor and causes a conformational change
2. Activated receptor binds to G protein and triggers release of GDP
3. GTP binds to alpha subunit and alpha subunit disscoates from beta/gamma
4. Alpha subunit binds to effector and activates it
5. GTP is hydrolyses and alpha subunit reassociates with beta/gamma

Question 5

examples of effectors

Answer 5

adenylyl cyclase, phospholipase C

Question 6

what does adenylyl cyclase do

Answer 6

converts ATP to cyclic AMP

Question 7

how is amount of cAMP regulated

Answer 7

adenylyl cyclase is regulated by types of alpha subunit on the G protein 
G alpha (I) inhibits adenylyl cyclase 
G alpha (S) stimulates adenylyl cyclase 
net amount of cAMP produced is regulated by the battle between G alpha (I) and G alpha (S)

Question 8

what is the function of cAMP

Answer 8

it activates PKA by binding to its 2 regulatory subunits

this releases its 2 active catalytic subunits

Question 9

what is CREB and what does it target

Answer 9

PKA phosphorylates CREB which is a transcription factor

once phosphorylated it can bind to other transcriptional transactivators to mediate transcription

Question 10

what does phospholipase C do

Answer 10

it is a downstream effector that converts PIP2 into IP3 and DAG

Question 11

what is the importance of IP3

Answer 11

it binds to its receptor on the ER
this allows the ER to release calcium into the cytosol
release calcium binds to channel to facilitate more release in positive feedback (up to certain concentration)
calcium activates PKC so it can phosphorylate target proteins

Question 12

role of inositol

Answer 12

inositol lipids are phosphorylated to form PIP2 which is then cut by phospholipase C