9.4 transmission and termination Flashcards
what are 2 similarities a G protein- coupled receptors have?
- similar structure with a single polypeptide chain that has seven transmembrane spanning regions, a ligand binding site and portion that binds with G protein on inside of cell.
- when activated they associate with a G protein
What occurs during the activation of a G protien?
for example when adrenaline binds to its Gprotien receptor GDP in the G protein is replaced by GTP and the G protein is activated. the GTP bound theta subunit then binds to and activates the adenylyl cyclase enzyme which converts ATP to cAMP.
when is a G protein on and when is it off?
when bound to a GTP it’s on
when bound to a GDP it’s off
cAMP is known as
a second messenger that binds and activates a kinases called protein kinase A (PKA)
what are second messengers?
signalling molecules found inside cells that relay information to the next target in the signal transduction pathway.
what does PKA do?
it phosphorylates and activates multiple protein targets.
how does the termination of a G protein signal occur?
- the signal molecule detaches from the receptor after a certain amount of time, inactivating the receptor so it can no longer bind to and activate the G protein
- within a very short time, an activated G protein deactivates itself by converting GTP to GDP
- Enzymes in the cytosol specifically degrade cAMP which stops the phosphorylation and activation of target proteins by PKA
- phosphatase remove phosphate groups from proteins causing them to be inactive.
what occurs when signalling a flight or fight response?
- receptor activation activates G protein
- G protein activates adenylyl cyclase
- adenylyl cyclase makes cAMP
- cAMP activates protein kinase A
5a. PKA phosphorylates glycogen synthase
5b. PKA activates GP kinase - GP kinase phosphorylates glycogen phosphorylase
