Question 1

Which of the following best describes the role of a second messenger in a signal transduction pathway?

Accepted Answer

It amplifies the signal initiated by the primary messenger.

Question 2

A mutation causes the Gα subunit of a G-protein to lose its intrinsic GTPase activity. What is the most likely cellular consequence?

Accepted Answer

The G-protein will be constitutively active, leading to prolonged signaling.

Question 3

Which of the following is a key difference between cell-surface and intracellular receptors?

Accepted Answer

Intracellular receptors often regulate gene expression directly by binding to DNA.

Question 4

Which of the following best explains why steroid hormones can bind to intracellular receptors?

Accepted Answer

They are hydrophobic and can diffuse across the plasma membrane.

Question 5

Which of the following is NOT a common method for terminating a signal transduction pathway?

Accepted Answer

Continuous activation of adenylate cyclase

Question 6

A patient is treated with tofacitinib, a JAK inhibitor. Which step in the JAK-STAT pathway is directly blocked by this drug?

Accepted Answer

Phosphorylation of STAT proteins

Question 7

Which of the following best describes the function of the Na+/K+ ATPase in maintaining membrane potential?

Accepted Answer

It actively transports 3 Na+ ions out and 2 K+ ions in, creating a negative membrane potential.

Question 8

Which of the following is a direct effect of epinephrine binding to β-adrenergic receptors in liver cells?

Accepted Answer

Activation of adenylate cyclase and increased cAMP production

Question 9

Which of the following second messengers is produced by the action of phospholipase C (PLC) on PIP2?

Accepted Answer

IP3 and DAG

Question 10

A researcher adds a drug that blocks the activity of phosphodiesterase in a cell. What is the expected effect on cAMP levels?

Accepted Answer

cAMP levels will increase due to decreased degradation.

Question 11

Which of the following best describes the mechanism by which ligand-gated ion channels contribute to neuronal signaling?

Accepted Answer

They open in response to ligand binding, allowing ions to flow and propagate electrical signals.

Question 12

Which of the following is a correct sequence of events in the activation of a receptor tyrosine kinase (RTK)?

Accepted Answer

Ligand binding, receptor dimerization, autophosphorylation, activation of downstream signaling proteins

Question 13

Which of the following is a primary messenger that acts through endocrine signaling?

Accepted Answer

Cortisol

Question 14

Which of the following best explains why second messengers are important in cell signaling?

Accepted Answer

They allow for signal amplification and diversification within the cell.

Question 15

Which of the following is a direct effect of IP3 in the cell?

Accepted Answer

Opening of Ca2+ channels in the endoplasmic reticulum

Question 16

A mutation in the glucocorticoid receptor prevents its dissociation from heat shock proteins (HSPs). What is the most likely consequence?

Accepted Answer

The receptor will fail to translocate to the nucleus and cannot regulate gene expression.

Question 17

Which of the following is a common outcome of activating the MAPK cascade via growth factor signaling?

Accepted Answer

Phosphorylation of nuclear transcription factors such as Jun and Fos

Question 18

Which of the following best describes the function of calmodulin in signal transduction?

Accepted Answer

It binds Ca2+ and activates kinases that phosphorylate target proteins.

Question 19

Which of the following is a plausible result of a failure to terminate a signaling pathway?

Accepted Answer

Development of diseases such as cancer due to uncontrolled signaling

Question 20

Which of the following best describes the role of hormone response elements (HREs) in nuclear receptor signaling?

Accepted Answer

They are DNA sequences that bind activated nuclear receptors to regulate gene transcription.

Biosignaling: Mechanisms and Pathways in Cellular Communication

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