Q: A patient is exposed to cholera toxin, which locks G$ \alpha $ in the GTP-bound state. What is the downstream effect on cAMP levels and water movement in intestinal cells?

cAMP levels increase, causing efflux of Cl$ ^- $ and Na$ ^+ $ with water, resulting in diarrhea.

Question 1

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

Accepted Answer

Paracrine signaling acts on neighboring cells, while endocrine signaling involves hormones traveling through the bloodstream to distant target cells.

Question 2

A mutation causes a G-protein to be unable to hydrolyze GTP to GDP. What is the most likely cellular consequence?

Accepted Answer

The G-protein will remain permanently active, continuously transmitting the signal.

Question 3

Which of the following is a correct sequence in the general flow of cell signaling information?

Accepted Answer

Release of signaling molecules → Detection of signal → Signal transduction → Signal removal and response termination

Question 4

Which of the following is NOT a characteristic of G-protein coupled receptors (GPCRs)?

Accepted Answer

They possess intrinsic tyrosine kinase activity.

Question 5

A patient is exposed to cholera toxin, which locks G$ \alpha $ in the GTP-bound state. What is the downstream effect on cAMP levels and water movement in intestinal cells?

Accepted Answer

cAMP levels increase, causing efflux of Cl$ ^- $ and Na$ ^+ $ with water, resulting in diarrhea.

Question 6

Which of the following best explains the role of second messengers in cell signaling?

Accepted Answer

They are intracellular molecules generated in response to receptor activation, amplifying and propagating the signal.

Question 7

Which enzyme catalyzes the conversion of ATP to cyclic AMP (cAMP) in the adrenergic signaling pathway?

Accepted Answer

Adenylyl cyclase

Question 8

A researcher observes that a cell is producing a signal that only affects itself. Which type of signaling is this?

Accepted Answer

Autocrine

Question 9

Which of the following statements about receptor tyrosine kinases (RTKs) is TRUE?

Accepted Answer

RTKs are activated by ligand-induced clustering and autophosphorylation.

Question 10

What is the function of the SH2 domain in proteins that interact with activated RTKs?

Accepted Answer

It binds to phosphorylated tyrosine residues on RTKs.

Question 11

Which of the following best describes the MAPK pathway initiated by RTK activation?

Accepted Answer

It involves activation of Ras, which triggers a phosphorylation cascade leading to gene expression changes.

Question 12

Which of the following is an example of juxtacrine signaling?

Accepted Answer

Notch and Delta interaction between two adjacent cells.

Question 13

Which of the following statements about G-protein regulation is correct?

Accepted Answer

GEFs activate G-proteins by promoting GDP-GTP exchange.

Question 14

A scientist adds a drug that inhibits adenylyl cyclase in liver cells. What is the expected effect on glycogen breakdown in response to epinephrine?

Accepted Answer

Glycogen breakdown will decrease because cAMP production is blocked.

Question 15

Which of the following is a real-life example of a disease caused by dysregulation of G-protein signaling?

Accepted Answer

Cholera

Question 16

Which of the following best describes the concept of signaling crosstalk?

Accepted Answer

Activated components from one pathway can affect components of another pathway.

Question 17

Which of the following is a second messenger involved in propagating signals inside the cell?

Accepted Answer

Ca$ ^{2+} $

Question 18

Which of the following events occurs FIRST after ligand binding to a receptor tyrosine kinase (RTK)?

Accepted Answer

Clustering (dimerization) of the RTKs

Question 19

Which of the following best explains why cAMP is considered a 'second messenger'?

Accepted Answer

It is generated inside the cell in response to an extracellular signal and relays the signal to intracellular targets.

Question 20

Which of the following is a direct target of protein kinase A (PKA) in the cAMP signaling pathway?

Accepted Answer

Phosphorylase kinase

Cell Signalling: Mechanisms and Pathways

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