Question 1

Which of the following best describes the mechanism by which water-soluble hormones exert their effects on target cells?

Accepted Answer

They bind to plasma membrane receptors and activate second messenger systems such as cAMP.

Question 2

What is the primary role of the G protein in the cyclic AMP signaling mechanism?

Accepted Answer

To activate the effector enzyme adenylate cyclase after hormone binding.

Question 3

A hormone binds to its receptor in the plasma membrane, causing the receptor to change shape and activate a G protein. What happens next in the cAMP signaling pathway?

Accepted Answer

The G protein activates adenylate cyclase, which converts ATP to cAMP.

Question 4

Which of the following hormones is lipid-soluble and acts by directly activating genes inside the cell?

Accepted Answer

Thyroid hormone

Question 5

What is the function of protein kinases in the cAMP signaling pathway?

Accepted Answer

They phosphorylate various proteins, activating or inhibiting them.

Question 6

Which of the following statements about hormone amplification is correct?

Accepted Answer

A single hormone molecule binding to a receptor can generate millions of final product molecules.

Question 7

In the $$Ca^{2+}-$$calcium signaling mechanism, which enzyme splits a plasma membrane phospholipid to generate second messengers?

Accepted Answer

Phospholipase C

Question 8

Which of the following is NOT a typical effect produced by hormone action on target cells?

Accepted Answer

Directly hydrolyzing ATP to ADP

Question 9

A patient is given a drug that inhibits phosphodiesterase. What would be the expected effect on cAMP levels in the cell?

Accepted Answer

cAMP levels would increase and persist longer.

Question 10

Which of the following best explains why water-soluble hormones require membrane-bound receptors?

Accepted Answer

They are unable to diffuse across the lipid bilayer of the plasma membrane.

Question 11

Which of the following is a second messenger used by some hormones other than cAMP?

Accepted Answer

cGMP (cyclic guanosine monophosphate)

Question 12

What is the result of the receptor-hormone complex binding to DNA in the nucleus?

Accepted Answer

It initiates transcription of the gene to mRNA.

Question 13

Which of the following best describes the action of insulin on its target cells?

Accepted Answer

Insulin binds to a tyrosine kinase receptor, which phosphorylates its own tyrosines and initiates a cascade of protein phosphorylations.

Question 14

A hormone increases cAMP in liver cells. What is the likely cellular response?

Accepted Answer

Activation of enzymes that break down glycogen, releasing glucose to the blood.

Question 15

Which of the following is true regarding the specificity of hormone action?

Accepted Answer

A hormone influences only those tissue cells that have receptors for it.

Question 16

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

Accepted Answer

Hormone binds to receptor in the plasma membrane.

Question 17

Which of the following is a correct equation for the conversion of ATP to cAMP by adenylate cyclase?

Accepted Answer

$$ATP \rightarrow cAMP + PP_i$$

Question 18

Which of the following is a plausible consequence if a cell lacks the specific protein kinases required for cAMP signaling?

Accepted Answer

The cell would not respond to hormones that signal via cAMP.

Question 19

Which of the following best describes the role of calmodulin in the $$Ca^{2+}-$$calcium signaling mechanism?

Accepted Answer

Calmodulin binds $$Ca^{2+}$$ and activates enzymes that amplify the cellular response.

Question 20

Which of the following is a correct sequence of events for steroid hormone action?

Accepted Answer

Steroid hormone diffuses through plasma membrane → binds intracellular receptor → receptor-hormone complex binds DNA → initiates transcription → mRNA directs protein synthesis

Hormone Action Mechanisms: Second Messengers and Gene Activation

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