G Protein Coupled Receptors

Question 1

what do GPCRs respond to?

Answer 1

Ach and Adr

Question 2

what are they stimulated by?

Answer 2

• lipids
• ions
• senses
• peptides
• aa
• nucleotides

Question 3

describe GPCRs

Answer 3

• have 7 transmembrane domains

- the C terminus interacts with the G protein

Question 4

describe the G proteins

Answer 4

• present as a trimer
• have α, β and γ subunits
• α subunit attached to GDP

Question 5

what are the different types of α subunits and what response do they elicit?

Answer 5

• αs: interacts w adenyl cyclase to STIMULATE cAMP
• αi: interacts w adenyl cyclase to INHIBIT cAMP
• αq/α11: interacts w phospholipase C (PLC-β)
• α12: interacts w Rho

Question 6

what happens when an agonist binds to the GPCR?

Answer 6

• causes shift in affinity: GDP phosphorylates to GTP
• α subunit interacts w specific enzyme
• β and γ subunits dissociate from α subunit

Question 7

what is the function of adenyl cyclase?

Answer 7

• turns ATP into cAMP
• cAMP converts inactive protein kinase A (PKA) into active PKA
• activated PKA phosphorylates target proteins

Question 8

what is the function of phosphodiesterase and how do pharmacological companies manipulate PDE?

Answer 8

• breaks down adenyl cyclase
• drugs target PDE to inhibit function
• to keep [cAMP] up to increase biological effects

Question 9

describe the interaction between Gq/G11 and phospholipase C

Answer 9

• when the GPCR11 is activated, the α11 subunit activates phospholipase C
• phospholipase C binds to phosphatidylinositol bisphosphate (PIP2)
• PLC cleaves PIP2 into inositol triphosphate (IP3) and DAG
• IP3 can bind to it’s own receptors on organelles
• causes release of Ca2+