15B Assignment

Question 1

α subunit of G-protein is bound to _____________, that is replaced with __________________ upon activation of GPCR.

ADP, ATP

ATP, ADP

GTP, GDP

GDP, GTP

Answer 1

GDP, GTP

Question 2

Inactivation of the α subunit of a trimeric G protein in enhanced by ….…

GEF activity of GPCR.

GAP activity of RGS.

GEF activity of RGS.

GAP activity of GPCR.

Answer 2

GAP activity of RGS.

Question 3

cAMP is synthesized from ATP by…………

cAMP phosphodiesterase

cGMP phosphodiesterase

GPCR

adenylyl cyclase

Answer 3

adenylyl cyclase

Question 4

Response to a signal reaches a maximum level before it shuts itself off followed by another pulse of maximal response even in the presence of the signaling molecule leading to an oscillatory response due to…………

negative feedback with a long delay

persisting positive feedback.

lack of feedback.

Answer 4

negative feedback with a long delay

Question 5

PKA is activated by binding of cAMP to the ………

both regulatory and catalytic subunits

catalytic subunits

cAMP phosphodiesterase

regulatory subunits

Answer 5

regulatory subunits

Question 6

Which type of mutation in the regulatory subunits of PKA would lead to a permanently inactive state?

Mutation in the regulatory subunits that prevents the release of the catalytic subunits.

Mutation in the cAMP binding site in the regulatory subunits that results in permanent binding of cAMP.

Mutation in the regulatory subunits that prevents them from binding to the catalytic subunits.

Answer 6

Mutation in the regulatory subunits that prevents the release of the catalytic subunits.

Question 7

NO produced in endothelial cells diffuses across the membranes into smooth muscle cells to stimulate synthesis of cGMP by binding to…..

Adenylyl cyclase

cGMP phosphodiesterase

Guanylyl cyclase

protein kinase

Answer 7

Guanylyl cyclase

Question 8

NOS catalyzed deamination of which of these amino acids produces NO?

Serine

Arginine

Threonine

Tyrosine

Answer 8

Arginine

Question 9

Cholera toxin activates the alpha subunit of Gs by ADP ribosylation, which………

inhibits the GTP hydrolysis activity of alpha subunit.

activates the GTP hydrolysis activity of alpha subunit.

inhibits adenylyl cyclase activity.

activates GDP binding to alpha subunit.

Answer 9

inhibits the GTP hydrolysis activity of alpha subunit.

Question 10

Increase in cAMP levels by extracellular signals can be balanced by breakdown of cAMP by enzyme………

adenylyl cyclase

guanylyl cyclase

cAMP phosphodiesterase

protein kinase

Answer 10

cAMP phosphodiesterase

Question 11

Activation of phospholipase C by G protein leads to …….

inhibition of PKC.

cleavage of inositol phospholipids.

inhibition of calcium release from ER.

Answer 11

cleavage of inositol phospholipids.

Question 12

Exposure of target cells to prolonged signals can lead to desensitization of GPCR by……………….

binding of arrestin to phosphorylated GPCR.

dephosphorylation of GPCR.

continued interaction with G protein.

Answer 12

binding of arrestin to phosphorylated GPCR.

Question 13

IP3 produced by phospholipase C activation binds to IP3 receptors and leads to …….

a rise in magnesium levels.

a drop in cytosolic calcium levels.

an inhibition of calcium release from ER.

release of calcium from ER into cytosol.

Answer 13

release of calcium from ER into cytosol.