Question 1

Which of the following best describes the effect of inhibitory (Gi) GPCR signaling on adenylyl cyclase activity?

Accepted Answer

It decreases the activity of adenylyl cyclase, resulting in lower cAMP levels.

Question 2

A researcher adds a non-hydrolyzable GTP analog to a cell culture. What is the most likely effect on the Gs protein and cAMP production?

Accepted Answer

Gs will remain active, continuously stimulating adenylyl cyclase and increasing cAMP.

Question 3

Which of the following steps is directly inhibited by the binding of an inhibitory (Gi) GPCR to its ligand?

Accepted Answer

Activation of adenylyl cyclase

Question 4

What is the primary role of β-arrestin in GPCR desensitization?

Accepted Answer

It binds to phosphorylated GPCRs, preventing further G protein activation.

Question 5

Which of the following is TRUE regarding the difference between GPCR termination and GPCR desensitization?

Accepted Answer

GPCR termination promotes GPCR signaling, while GPCR desensitization overcomes the signal.

Question 6

A patient is given a drug that prevents β-arrestin from binding to GPCRs. What is the most likely consequence?

Accepted Answer

GPCRs will remain active longer, leading to prolonged cellular responses.

Question 7

Which enzyme is primarily responsible for phosphorylating the β-adrenergic receptor during desensitization?

Accepted Answer

β-adrenergic receptor kinase (βARK)

Question 8

What is the effect of repeated exposure to a ligand on GPCR signaling?

Accepted Answer

It leads to desensitization, reducing the cellular response even if the ligand is still present.

Question 9

Which of the following best explains why β-arrestin binding to a GPCR leads to receptor internalization?

Accepted Answer

β-arrestin acts as an adaptor protein, recruiting components of the endocytic machinery.

Question 10

Which of the following statements about β-arrestin and GPCRs is TRUE?

Accepted Answer

β-arrestin binds to phosphorylated residues on the carboxy-terminal region of GPCRs.

Question 11

A scientist observes that after prolonged exposure to epinephrine, the β-adrenergic receptor shows reduced responsiveness. What is the most likely explanation?

Accepted Answer

GPCR desensitization due to β-arrestin binding and receptor internalization.

Question 12

Which of the following is NOT directly involved in the desensitization of the β-adrenergic receptor?

Accepted Answer

Phospholipase C

Question 13

What is the immediate effect of GTP binding to the Gα subunit of a stimulatory G protein (Gs)?

Accepted Answer

Activation of adenylyl cyclase and increased cAMP production

Question 14

Which of the following best describes the role of cAMP in GPCR signaling?

Accepted Answer

It acts as a secondary messenger, amplifying the signal inside the cell.

Question 15

A mutation prevents the hydrolysis of GTP to GDP on the Gα subunit. What is the most likely cellular consequence?

Accepted Answer

Prolonged activation of the downstream effector enzyme (e.g., adenylyl cyclase)

Adenylyl Cyclase Regulation and GPCR Desensitization in Signal Transduction

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