G protein linked Flashcards
structure of a G protein coupled receptor
they are 7 transmembrane receptors so have 7 transmembrane helices
what is the difference between the first and secondary messenger
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
structure of a G protein
3 domains, alpha beta gamma
beta and gamma domains never separate
alpha subunit can bind GTP/GDP and dissociate from beta/gamma domains
steps of G protein activation cycle
- hormone binds to G protein coupled receptor and causes a conformational change
- Activated receptor binds to G protein and triggers release of GDP
- GTP binds to alpha subunit and alpha subunit disscoates from beta/gamma
- Alpha subunit binds to effector and activates it
- GTP is hydrolyses and alpha subunit reassociates with beta/gamma
examples of effectors
adenylyl cyclase, phospholipase C
what does adenylyl cyclase do
converts ATP to cyclic AMP
how is amount of cAMP regulated
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)
what is the function of cAMP
it activates PKA by binding to its 2 regulatory subunits
this releases its 2 active catalytic subunits
what is CREB and what does it target
PKA phosphorylates CREB which is a transcription factor
once phosphorylated it can bind to other transcriptional transactivators to mediate transcription
what does phospholipase C do
it is a downstream effector that converts PIP2 into IP3 and DAG
what is the importance of IP3
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
role of inositol
inositol lipids are phosphorylated to form PIP2 which is then cut by phospholipase C