Test 1 Biochem

Question 1

what is the structure of GCPRs?

Answer 1

7 membrane spanning proteins with the amino terminus projecting outside of the cell and the carboxy termin pointing inwards.

Question 2

What are the different types of trimeric G proteins and how many of them are they?

Answer 2

alpha (21), beta (6) and gamma (12)

Question 3

Describe the function of the trimeric G proteins?

Answer 3

normally the alpha subunits are GDP bound in the off stage. A ligand binds, a conformation change occurs in the GCPR, and acts as a guanine nucleotide factor allowing the release of GDP and the binding of GTP. From this a conformation change between alpha and beta occurs and engages different downstream signaling pathways.

Question 4

What are the second messengers affected by GCPRs?

Answer 4

cAMP, inositol triphosphate, diacylglycerol, calcium, and RhoA GTPases.

Question 5

What are the sympathetic effects on cardiac muscle?

Answer 5

G-alpha-s stimulates adenylate cyclase, increasing cAMP levels. cAMP then activates protein kinase A which causes in increase in the cytoplasmic concentrations of Calcium. This increase causes an increase in the activity of the L type calcium channels and the Ryanodine receptor (SR).

Question 6

What are the parasympathetic effects on cardiac muscle?

Answer 6

M2 muscarinic receptors stimulates G-alpha-i. G-alpha-i inhibits adenylate cyclase leaving phosphodiesterase causing cAMP levels to decrease. This results in a lower level of cytoplasmic calcium concentrations leading to relaxation.