Question 1

Which of the following best describes the role of cell-surface receptor proteins in cell signaling?

Accepted Answer

They bind extracellular signal molecules and relay signals into the cell via intracellular signaling proteins.

Question 2

A cell receives both signals A and B, which together trigger survival, but receives only signal C, which triggers differentiation. What will happen if the cell receives signals A, B, and C simultaneously?

Accepted Answer

The cell will survive and differentiate, responding to the combination of signals.

Question 3

Which type of extracellular signaling involves a signaling cell and a target cell in direct physical contact, with the signal molecule remaining bound to the membrane of the signaling cell?

Accepted Answer

Contact-dependent signaling

Question 4

Acetylcholine can cause different responses in different cell types. In heart pacemaker cells, it decreases the rate of firing, while in skeletal muscle cells, it causes contraction. What is the most likely explanation for this phenomenon?

Accepted Answer

Different cell types have distinct receptor proteins and intracellular signaling pathways.

Question 5

Which of the following is a correct sequence for G-protein-coupled receptor activation?

Accepted Answer

Signal molecule binds receptor → receptor activates G protein → G protein activates enzyme

Question 6

Which equation best represents the phosphorylation cycle in cell signaling?

Accepted Answer

$$\mathrm{Protein} + \mathrm{ATP} \xrightarrow{\mathrm{kinase}} \mathrm{Protein{-}P} + \mathrm{ADP}$$

Question 7

A mutation causes a cell to overexpress a receptor protein on its surface. Which of the following is a likely consequence?

Accepted Answer

The cell may receive excessive signaling, potentially leading to uncontrolled growth or cancer.

Question 8

Which of the following mechanisms allows cells to adjust their sensitivity to a signal?

Accepted Answer

Receptor destruction in lysosomes

Question 9

What is the role of scaffold proteins in intracellular signaling complexes?

Accepted Answer

They anchor inactive intracellular signaling proteins near the receptor, facilitating rapid signal transduction.

Question 10

Which feedback mechanism can generate an all-or-none response in cell signaling?

Accepted Answer

Positive feedback

Question 11

A cell responds abruptly to a gradually increasing concentration of a signal molecule. Which type of response curve best describes this behavior?

Accepted Answer

All-or-none

Question 12

Which of the following statements about GTPases is correct?

Accepted Answer

GEFs (Guanine nucleotide exchange factors) activate GTPases by facilitating GDP release and GTP binding.

Question 13

Which of the following is a direct effect of protein kinase activity in a signaling pathway?

Accepted Answer

Addition of phosphate groups to proteins, altering their activity

Question 14

In endocrine signaling, which equation best describes the movement of the signal molecule?

Accepted Answer

$$	ext{Endocrine cell} \xrightarrow{	ext{hormone}} 	ext{bloodstream} \xrightarrow{	ext{hormone}} 	ext{target cell}$$

Question 15

Which of the following is NOT a way that cells can decrease their sensitivity to a signal?

Accepted Answer

Increasing the number of cell-surface receptors

Question 16

A researcher observes that a cell’s response to a signal is much slower than expected, taking hours instead of seconds. Which process is most likely responsible for this slow response?

Accepted Answer

Altered protein synthesis via changes in gene expression

Question 17

Which of the following best explains the importance of rapid turnover of intracellular signaling molecules?

Accepted Answer

It enables cells to quickly adjust their response to changes in signal molecule concentration.

Question 18

Which modular interaction domain is responsible for binding to phosphorylated tyrosine residues on activated receptors?

Accepted Answer

SH2 domain

Question 19

A cell receives a signal that activates a protein kinase, which then phosphorylates an inhibitor protein bound to a transcription regulator. What is the immediate result?

Accepted Answer

The inhibitor protein releases the transcription regulator, allowing gene expression.

Question 20

Which of the following best describes the effect of negative feedback with a long delay in a signaling pathway?

Accepted Answer

It causes oscillations in the activity of the signaling molecule.

Principles of Cell Signaling: Mechanisms and Responses

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