Q: Which equation correctly represents the conversion of ATP to cAMP by adenylyl cyclase?

$$\text{ATP} \xrightarrow{\text{adenylyl cyclase}} \text{cAMP} + \text{PP}_i$$

Question 1

Which of the following best describes the difference between cell-surface receptors and intracellular receptors?

Accepted Answer

Cell-surface receptors are embedded in the plasma membrane and bind extracellular signal molecules, while intracellular receptors are located inside the cell and bind small hydrophobic molecules that can cross the membrane.

Question 2

Which of the following is NOT a type of cell-surface receptor?

Accepted Answer

Steroid hormone receptor

Question 3

A signal molecule binds to a G-protein-coupled receptor (GPCR). What is the immediate next step in the signaling pathway?

Accepted Answer

The receptor activates a G protein by causing the α subunit to exchange GDP for GTP.

Question 4

Which equation correctly represents the conversion of ATP to cAMP by adenylyl cyclase?

Accepted Answer

$$	ext{ATP} \xrightarrow{	ext{adenylyl cyclase}} 	ext{cAMP} + 	ext{PP}_i$$

Question 5

In the cAMP signaling pathway, which enzyme is activated by cAMP to phosphorylate target proteins?

Accepted Answer

Protein kinase A (PKA)

Question 6

Which step in the epinephrine-stimulated breakdown of glycogen in skeletal muscle cells does NOT amplify the original signal?

Accepted Answer

Activation of glycogen phosphorylase by phosphorylase kinase

Question 7

Which of the following best describes the role of IP3 in the inositol phospholipid pathway?

Accepted Answer

IP3 binds to Ca2+ channels in the endoplasmic reticulum, causing Ca2+ release into the cytosol.

Question 8

Which protein is most commonly responsible for binding Ca2+ and mediating its effects in the cytosol?

Accepted Answer

Calmodulin

Question 9

Nitric oxide (NO) acts as a signaling molecule in blood vessels. Which of the following best explains its mechanism of action?

Accepted Answer

NO diffuses across cell membranes and activates guanylyl cyclase, increasing cGMP and causing muscle relaxation.

Question 10

Which of the following is a key advantage of multistep intracellular signaling cascades?

Accepted Answer

They allow for amplification and adaptation of the incoming signal.

Question 11

Which class of enzyme-coupled receptors is most commonly involved in regulating cell growth, proliferation, and survival?

Accepted Answer

Receptor tyrosine kinases (RTKs)

Question 12

Which of the following statements about G proteins is TRUE?

Accepted Answer

G proteins are activated when the α subunit exchanges GDP for GTP.

Question 13

Cholera toxin causes disease by modifying the Gs α subunit. What is the result of this modification?

Accepted Answer

Gs α subunit cannot hydrolyze GTP, resulting in prolonged activation and excessive Cl- and water outflow.

Question 14

Which of the following is a function of scaffold proteins in intracellular signaling pathways?

Accepted Answer

They bring together components needed to propagate the signal.

Question 15

Which equation best represents the hydrolysis of GTP by the G protein α subunit?

Accepted Answer

$$	ext{GTP} \xrightarrow{	ext{GTPase}} 	ext{GDP} + 	ext{P}_i$$

Question 16

Which of the following is a plausible consequence of a mutation that prevents the dimerization of receptor tyrosine kinases (RTKs)?

Accepted Answer

The receptor would fail to activate its kinase activity, preventing downstream signaling.

Question 17

Which of the following best describes the role of diacylglycerol (DAG) in the inositol phospholipid pathway?

Accepted Answer

DAG remains in the plasma membrane and helps activate protein kinase C (PKC).

Question 18

Which of the following is a real-world example of a rapid cellular response mediated by cell-surface receptors?

Accepted Answer

Acetylcholine binding to ion-channel-coupled receptors to trigger muscle contraction.

Question 19

Which of the following statements about Ca2+ signaling is TRUE?

Accepted Answer

Ca2+ pumps maintain a steep electrochemical gradient by removing Ca2+ from the cytosol.

Cell Signaling: Principles, Pathways, and Receptors

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