Question 1

Which of the following best describes the difference between endocrine and paracrine signaling?

Accepted Answer

Endocrine signaling involves hormones traveling through the bloodstream to distant target cells, while paracrine signaling involves local mediators acting on nearby cells.

Question 2

A mutation in a G protein-coupled receptor (GPCR) prevents it from binding GTP. What is the most likely consequence for the cell?

Accepted Answer

The G protein will remain in its inactive GDP-bound state, and downstream signaling will not occur.

Question 3

Which of the following is a direct result of phospholipase C activation in a cell signaling pathway?

Accepted Answer

Hydrolysis of PIP$$_2 to $$generate IP$$_3$$ and DAG

Question 4

Why can both glucagon and epinephrine trigger glycogen breakdown in the liver, even though they bind to different GPCRs?

Accepted Answer

Both receptors activate the same intracellular signaling cascade, leading to the same cellular response.

Question 5

Which of the following best explains the amplification of a signal in a kinase cascade?

Accepted Answer

Each kinase can phosphorylate multiple downstream targets, resulting in exponential signal amplification.

Question 6

Aspirin inhibits cyclooxygenase (COX). What is the biochemical consequence of this inhibition?

Accepted Answer

Reduced synthesis of prostaglandins and thromboxanes from arachidonate

Question 7

Which of the following mutations in a GPCR would most likely result in a loss of receptor function?

Accepted Answer

A mutation that prevents ligand binding to the receptor

Question 8

In the PI3K/Akt pathway, what is the role of PTEN?

Accepted Answer

PTEN dephosphorylates PIP$$_3 to $$PIP$$_2$$, thereby inhibiting Akt activation.

Question 9

A patient with whooping cough is infected with Bordetella pertussis, which modifies the inhibitory G protein (G$$_i). $$What is the expected effect on cAMP levels in the patient's cells?

Accepted Answer

cAMP levels will increase because inhibition of adenylate cyclase is blocked.

Question 10

Which of the following best describes the sequence of events leading to NFAT activation in T cells?

Accepted Answer

Increased cytosolic Ca$$^{2+}$$ activates calcineurin, which dephosphorylates NFAT, exposing its nuclear localization signal.

Question 11

Which of the following is a property of enzyme-linked receptors such as receptor tyrosine kinases?

Accepted Answer

They autophosphorylate on tyrosine residues upon ligand binding.

Question 12

Which chemical feature explains why IP$$_3$$ and DAG, produced from PIP$$_2 by $$phospholipase C, have different cellular locations?

Accepted Answer

IP$$_3 is $$highly polar and soluble in the cytosol, while DAG is hydrophobic and remains in the membrane.

Question 13

Which of the following is a direct effect of Akt activation in the PI3K pathway?

Accepted Answer

Promotion of cell survival and inhibition of apoptosis

Question 14

Which of the following best explains why acetylcholine, a small charged molecule, requires a surface receptor?

Accepted Answer

Its charge prevents it from crossing the hydrophobic plasma membrane.

Question 15

Which of the following is a likely outcome if a cell reduces the number of surface receptors for a signaling molecule?

Accepted Answer

The cell's sensitivity to the signaling molecule decreases.

Question 16

Which of the following steps in the Ras-MAPK pathway is directly responsible for the activation of ERK?

Accepted Answer

Phosphorylation of ERK by MEK

Question 17

Which of the following is a real-world example of signal termination in cell signaling?

Accepted Answer

Phosphodiesterase hydrolyzing cAMP to AMP

Question 18

Which of the following best describes the effect of cross-talk between signaling pathways?

Accepted Answer

It allows integration and coordination of multiple signals for a unified cellular response.

Question 19

If a kinase cascade consists of 10 relay enzymes, each activating 10 kinases, and each kinase activates 10 targets, how many modified targets are produced?

Accepted Answer

$$10^{3} = 1000$

Cell Signaling and Biosignaling Pathways in Biochemistry

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