Question 1

Which of the following best describes the role of a receptor in cell signaling?

Accepted Answer

A receptor is a protein that binds to extracellular messenger molecules and transmits signals into the cell, initiating intracellular changes.

Question 2

A neurotransmitter binds to an ion channel receptor on a neuron, causing the channel to open and allow Na$^+$ ions to enter the cell. What is the immediate result of this event?

Accepted Answer

The membrane potential of the neuron changes, potentially leading to the initiation of an action potential.

Question 3

Which of the following is TRUE regarding G-protein coupled receptors (GPCRs)?

Accepted Answer

GPCRs activate intracellular enzymes by coupling with G-proteins when a ligand binds to them.

Question 4

A hydrophilic hormone cannot cross the plasma membrane. How does it typically exert its effects on a target cell?

Accepted Answer

By binding to a surface receptor, which then activates a second messenger pathway inside the cell.

Question 5

Which of the following best explains the concept of signal amplification in a second messenger pathway?

Accepted Answer

A single ligand binding event can lead to the activation of many intracellular molecules, resulting in a large cellular response.

Question 6

Which of the following is the correct sequence of events in the G-protein coupled receptor (GPCR) second messenger pathway?

Accepted Answer

Ligand binds to receptor $\rightarrow$ G protein is activated $\rightarrow$ Enzyme is activated $\rightarrow$ Second messenger is produced

Question 7

A patient is given a drug that inhibits adenylyl cyclase. Which step in the signal transduction pathway would be directly affected?

Accepted Answer

The synthesis of cyclic AMP (cAMP) as a second messenger would be reduced.

Question 8

Which of the following statements about hydrophobic hormones is correct?

Accepted Answer

They cross the plasma membrane and bind to intracellular receptors, often affecting gene transcription.

Question 9

A mutation causes a cell to lack surface receptors for a specific hydrophilic hormone. What is the most likely consequence?

Accepted Answer

The cell will not respond to the hormone because the hormone cannot enter the cell or trigger a signaling cascade.

Question 10

Which of the following best describes the function of protein kinase A in the cAMP second messenger pathway?

Accepted Answer

Protein kinase A phosphorylates target proteins, leading to changes in their activity and cellular response.

Question 11

A researcher adds a molecule that mimics the ligand for a GPCR but cannot activate the receptor. What is the most likely effect on the cell?

Accepted Answer

The molecule will competitively inhibit the natural ligand, preventing signal transduction.

Question 12

Which of the following is a key difference between ion channel receptors and G-protein coupled receptors?

Accepted Answer

Ion channel receptors directly allow ions to cross the membrane, while GPCRs activate intracellular signaling cascades.

Question 13

Which of the following best explains why hydrophilic hormones require cell surface receptors?

Accepted Answer

Hydrophilic hormones cannot cross the hydrophobic core of the plasma membrane.

Question 14

A cell is exposed to a ligand that binds to a GPCR, leading to the following sequence: activation of adenylyl cyclase, increased cAMP, activation of protein kinase A, and phosphorylation of enzymes. Which equation best represents the amplification of the signal at the cAMP step?

Accepted Answer

$	ext{ATP} \xrightarrow{	ext{adenylyl cyclase}} 	ext{cAMP}$

Question 15

Which of the following is an example of a cellular response that could result from signal transduction via a surface receptor?

Accepted Answer

Activation of enzymes that break down glycogen in response to adrenaline.

Question 16

A mutation in a G protein prevents it from binding GTP. What is the most likely effect on the cell signaling pathway?

Accepted Answer

The G protein will remain inactive, and the downstream signaling cascade will not be initiated.

Question 17

Which of the following best describes the role of the receptor-hormone complex formed by hydrophobic hormones?

Accepted Answer

It binds to DNA in the nucleus and regulates gene transcription.

Question 18

Which of the following is NOT a stage in the general process of cell-to-cell signaling?

Accepted Answer

Replication

Question 19

A cell receives a signal from a hydrophobic hormone. Which of the following steps is most likely to occur LAST in the signaling process?

Accepted Answer

Translation of mRNA into new proteins.

Cell to Cell Communication: Receptor Signaling and Signal Transduction

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