Q: Which equation correctly represents the activation of a G protein by a GPCR?

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

Question 1

Which of the following best distinguishes paracrine signaling from endocrine signaling in multicellular organisms?

Accepted Answer

Paracrine signaling involves local mediators affecting nearby cells, while endocrine signaling uses hormones that travel through the bloodstream to distant targets.

Question 2

Which of the following is a key difference between steroid hormone receptors and peptide hormone receptors?

Accepted Answer

Steroid hormone receptors are intracellular and directly affect gene expression, while peptide hormone receptors are membrane-bound and activate second messenger pathways.

Question 3

A cell receives a signal via a G protein-coupled receptor (GPCR). Which of the following is the correct sequence of events?

Accepted Answer

Ligand binds GPCR → GPCR activates G protein → G protein exchanges GDP for GTP → Effector enzyme activated → Second messenger produced

Question 4

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

Accepted Answer

Kinases transfer phosphate groups from ATP to specific substrates, often activating or deactivating proteins.

Question 5

What is the role of cAMP in the signal transduction pathway initiated by epinephrine binding to its receptor?

Accepted Answer

cAMP serves as a second messenger, activating protein kinase A (PKA) to phosphorylate target proteins.

Question 6

Which equation correctly represents the activation of a G protein by a GPCR?

Accepted Answer

$$	ext{G protein-GDP} + 	ext{GPCR-ligand} ightarrow 	ext{G protein-GTP} + 	ext{GPCR}$$

Question 7

A mutation causes a G protein to remain in its 'active' GTP-bound state. What is the most likely cellular consequence?

Accepted Answer

The signal transduction pathway will be continuously activated, potentially leading to uncontrolled cell growth.

Question 8

Which of the following best explains the function of phosphatases in a phosphorylation cascade?

Accepted Answer

Phosphatases remove phosphate groups from proteins, often deactivating them and terminating the signal.

Question 9

Which of the following is a direct result of ligand binding to a receptor tyrosine kinase (RTK)?

Accepted Answer

The receptor undergoes autophosphorylation, creating docking sites for intracellular signaling proteins.

Question 10

Which of the following best describes the mechanism of action of steroid hormone receptors?

Accepted Answer

Steroid hormones bind to intracellular receptors, which then act as transcription factors to regulate gene expression.

Question 11

Which of the following is NOT a second messenger commonly involved in signal transduction?

Accepted Answer

ATP

Question 12

A researcher observes that a cell's response to a hormone is diminished when gap junctions are blocked. What does this suggest about the signaling mechanism?

Accepted Answer

The hormone relies on direct cell-to-cell communication through gap junctions (juxtacrine signaling).

Question 13

Which of the following best describes the role of transcription factors in signal transduction?

Accepted Answer

Transcription factors are proteins that bind DNA and regulate gene expression in response to signaling pathways.

Question 14

Which of the following events occurs after activation of adenylyl cyclase by a G protein?

Accepted Answer

Adenylyl cyclase converts ATP to cAMP, which then activates protein kinase A (PKA).

Question 15

Which of the following is the correct formula for the phosphorylation of a protein by a kinase?

Accepted Answer

$$	ext{Protein} + 	ext{ATP} \xrightarrow{	ext{Kinase}} 	ext{Protein-P} + 	ext{ADP}$$

Question 16

A patient has a genetic defect in their G protein-coupled receptor (GPCR) that prevents GDP from being exchanged for GTP. What is the most likely effect on signal transduction?

Accepted Answer

The G protein will remain inactive, and the signal transduction pathway will not be activated.

Question 17

Which of the following best describes the general events following ligand binding to a G protein-coupled receptor?

Accepted Answer

Ligand binds GPCR → GPCR activates G protein → G protein activates effector enzyme → Second messenger produced → Cellular response

Question 18

Which of the following is a common misconception about the function of second messengers?

Accepted Answer

Second messengers are always proteins that directly activate transcription.

Question 19

Which of the following is a correct description of the phosphorylation cascade in signal transduction?

Accepted Answer

A series of kinases sequentially phosphorylate each other, amplifying the signal and leading to a cellular response.

Cell Signaling: Mechanisms and Hormone Action (Chapter 5.6 Study Guide)

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