Q: Which equation best represents the exchange that occurs during G-protein activation?

$$\mathrm{G\text{-}protein{-}GDP} + GTP \rightarrow \mathrm{G\text{-}protein{-}GTP} + GDP$$

Question 1

Which type of membrane protein is the G-protein depicted in the diagram, given that it is only associated with the inner face of the cell membrane?

Accepted Answer

Peripheral membrane protein

Question 2

In the first step of G-protein coupled receptor (GPCR) signaling, the ligand binds to the receptor protein. What is the immediate effect of ligand binding on the receptor?

Accepted Answer

It activates the receptor, allowing it to interact with the G-protein.

Question 3

After the ligand binds to the GPCR, the G-protein is activated. Which molecule is exchanged on the G-protein during this activation?

Accepted Answer

GDP is replaced by GTP

Question 4

What is the role of the second messenger released in the final step of GPCR signaling?

Accepted Answer

It activates proteins in the cytoplasm to propagate the signal.

Question 5

If a mutation prevents the G-protein from binding GTP, what would be the most likely consequence for cell signaling?

Accepted Answer

The cell would be unable to activate downstream signaling pathways.

Question 6

Which of the following best describes the location of the G-protein after activation by the receptor?

Accepted Answer

It dissociates from the receptor and moves along the inner face of the membrane.

Question 7

Which equation best represents the exchange that occurs during G-protein activation?

Accepted Answer

$$\mathrm{G	ext{-}protein{-}GDP} + GTP ightarrow \mathrm{G	ext{-}protein{-}GTP} + GDP$$

Question 8

A researcher adds a non-hydrolyzable GTP analog to a cell. What effect would this have on G-protein signaling?

Accepted Answer

G-proteins would remain in the active state, continuously signaling.

Question 9

Which of the following is a real-world example of a disease caused by malfunction in GPCR signaling?

Accepted Answer

Cholera

Question 10

If the receptor protein is mutated so that it cannot bind the ligand, what is the most likely outcome for the G-protein?

Accepted Answer

The G-protein will remain inactive and bound to GDP.

Question 11

Which step in the GPCR pathway involves a conformational change in the receptor protein?

Accepted Answer

Ligand binding to the receptor

Question 12

What is the primary function of the G-protein in cell signaling?

Accepted Answer

To relay signals from the receptor to intracellular effectors

Question 13

Which of the following best describes the relationship between the receptor protein and the G-protein before ligand binding?

Accepted Answer

They are physically associated but the G-protein is inactive.

Question 14

A drug blocks the dissociation of the G-protein from the receptor after activation. What is the most likely effect?

Accepted Answer

Signal transduction would be impaired because the G-protein could not activate downstream effectors.

Question 15

Which of the following is NOT a function of second messengers in GPCR signaling?

Accepted Answer

Transporting the ligand across the membrane

Question 16

Which of the following best explains why G-proteins are considered peripheral membrane proteins?

Accepted Answer

They are attached to the inner surface of the membrane but do not span it.

Question 17

Which process is responsible for terminating the signal in GPCR pathways?

Accepted Answer

Hydrolysis of GTP to GDP by the G-protein

Question 18

A patient has a genetic defect that prevents the release of second messengers in GPCR signaling. What is the most likely cellular consequence?

Accepted Answer

The cell will fail to respond to extracellular signals.

Question 19

Which of the following steps in GPCR signaling is most directly responsible for the amplification of the signal?

Accepted Answer

Release of second messengers

Question 20

In a multi-step signaling pathway, which equation best represents the overall process of signal transduction from ligand binding to second messenger release?

Accepted Answer

$$	ext{Ligand} + 	ext{Receptor} ightarrow 	ext{Activated Receptor}$$ 
 $$	ext{Activated Receptor} + 	ext{G	ext{-}protein{-}GDP} ightarrow 	ext{G	ext{-}protein{-}GTP}$$ 
 $$	ext{G	ext{-}protein{-}GTP} ightarrow 	ext{Second Messenger Release}$$

G-Protein Coupled Receptors and Signal Transduction

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