Question 1

Which of the following best describes the structure of a G protein-coupled receptor (GPCR)?

Accepted Answer

A protein with 7 transmembrane alpha-helices

Question 2

What is the primary function of the G protein in the GPCR signaling pathway?

Accepted Answer

To bind and hydrolyze GTP, transmitting the signal inside the cell

Question 3

Which of the following equations correctly represents the hydrolysis of GTP by the G protein?

Accepted Answer

$$GTP \rightarrow GDP + P_i$$

Question 4

Upon ligand binding, what conformational change occurs in the GPCR?

Accepted Answer

The receptor undergoes a conformational change that activates the associated G protein

Question 5

Which of the following is NOT an essential component of GPCR signal transduction?

Accepted Answer

Direct phosphorylation of the ligand

Question 6

What is the role of the alpha subunit of the G protein after GTP binding?

Accepted Answer

It dissociates from the beta and gamma subunits and interacts with the effector enzyme

Question 7

Which of the following statements about inhibitory G proteins ($$G_i) is $$correct?

Accepted Answer

$$G_i$$ proteins inhibit the effector enzyme, decreasing the secondary messenger

Question 8

A mutation prevents the hydrolysis of GTP by the G protein alpha subunit. What is the most likely cellular consequence?

Accepted Answer

Prolonged activation of the effector enzyme

Question 9

Which equation best represents the activation of adenylyl cyclase by a stimulatory G protein ($$G_s$$)?

Accepted Answer

$$ATP \rightarrow cAMP + P_i$$

Question 10

Which of the following is a direct result of secondary messenger activation in GPCR signaling?

Accepted Answer

Opening of ion channels

Question 11

In the context of GPCR signaling, which step is most likely to be affected by a non-functional GTPase activity in the G protein?

Accepted Answer

Termination of the signal

Question 12

Which of the following best explains why GPCRs are considered versatile signaling molecules?

Accepted Answer

They interact with multiple types of G proteins, leading to diverse cellular responses

Question 13

Which of the following is a common misconception about GPCRs?

Accepted Answer

GPCRs directly hydrolyze GTP

Question 14

A patient has a genetic mutation that causes the G protein alpha subunit to remain bound to GTP. What is the most likely effect on cellular signaling?

Accepted Answer

Continuous activation of downstream signaling pathways

Question 15

Which of the following steps occurs FIRST in the GPCR signaling pathway?

Accepted Answer

Ligand binds to the GPCR

Question 16

Which of the following is the correct sequence of events in GPCR signal transduction?

Accepted Answer

Ligand binding → GPCR conformational change → G protein activation → Effector enzyme activation → Secondary messenger production

Question 17

Which of the following is a function of the beta and gamma subunits of the G protein after activation?

Accepted Answer

They remain associated with the membrane and can modulate ion channels

Question 18

Which of the following is a real-world example of a physiological process regulated by GPCRs?

Accepted Answer

Vision in the retina

Question 19

Which of the following best describes the role of secondary messengers in GPCR signaling?

Accepted Answer

They amplify the signal and mediate cellular responses

Question 20

Which of the following is the correct formula for the production of cAMP from ATP by adenylyl cyclase?

Accepted Answer

$$ATP \rightarrow cAMP + PP_i$$

G Protein-Coupled Receptors (GPCRs) and Signal Transduction

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