Question 1

Which of the following best describes the role of GTPase-activating proteins (GAPs) in G protein signaling?

Accepted Answer

They hydrolyze GTP to GDP, inactivating the G protein.

Question 2

A mutation causes a cell to express twice the normal number of EGF receptors. What is the most likely cellular consequence?

Accepted Answer

The cell will become hypersensitive to EGF, increasing proliferation.

Question 3

Which of the following is a correct sequence of events in a typical GPCR signaling pathway?

Accepted Answer

Ligand binds receptor → G protein exchanges GDP for GTP → Adenylyl cyclase is activated → cAMP is produced

Question 4

Which type of signaling involves a cell responding to a signal it released itself?

Accepted Answer

Autocrine signaling

Question 5

A small, nonpolar signaling molecule is most likely to:

Accepted Answer

Diffuse through the plasma membrane and bind an intracellular receptor

Question 6

Which of the following best explains why signal amplification is important in cell signaling?

Accepted Answer

It allows a small number of receptors to produce a large cellular response.

Question 7

Which of the following is a second messenger in the GPCR pathway that activates protein kinase A?

Accepted Answer

cAMP

Question 8

A drug that binds to a receptor and prevents the natural ligand from activating it, but does not trigger a response itself, is called:

Accepted Answer

An antagonist

Question 9

Which of the following scenarios best illustrates paracrine signaling?

Accepted Answer

A neurotransmitter is released at a synapse and acts on an adjacent neuron.

Question 10

Which of the following statements about receptor affinity is correct?

Accepted Answer

A low Kd value indicates high affinity for the ligand.

Question 11

Which of the following is NOT a typical cellular response to signal transduction?

Accepted Answer

Direct synthesis of ATP from the receptor

Question 12

In the context of neurotransmitter signaling, what is the primary effect of cocaine on dopamine signaling?

Accepted Answer

It blocks dopamine reuptake, increasing dopamine in the synaptic cleft.

Question 13

Which of the following best describes the function of protein kinases in signal transduction?

Accepted Answer

They add phosphate groups to proteins, often altering their activity.

Question 14

Which of the following is true about the structure of G protein-coupled receptors (GPCRs)?

Accepted Answer

They have seven transmembrane domains.

Question 15

A researcher uses a protease to remove all cell surface proteins. The cell still responds to a signaling molecule. What is the most likely explanation?

Accepted Answer

The receptor for this signal is inside the cell, and the signaling molecule is nonpolar and can diffuse into the cell.

Question 16

Which of the following best describes the role of second messengers in signal transduction?

Accepted Answer

They are small molecules that amplify and distribute signals within the cell.

Question 17

Which of the following is a direct result of epinephrine binding to a beta-adrenergic receptor on a liver cell?

Accepted Answer

Activation of adenylyl cyclase and increased glucose release

Question 18

Which of the following is the correct formula for the dissociation constant $$K_d of a $$receptor-ligand interaction?

Accepted Answer

$$K_d = \frac{[R][L]}{[RL]}$$

Question 19

Which of the following is a function of calmodulin in cell signaling?

Accepted Answer

It binds Ca2+ and undergoes a conformational change to regulate target proteins.

Question 20

Which of the following best describes the effect of an agonist drug on a receptor?

Accepted Answer

It binds and activates the receptor, mimicking the natural ligand.

Cell Signaling and Signal Transduction Mechanisms

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