Question 1

Which of the following cell junctions in animal cells is primarily responsible for preventing the leakage of extracellular fluid across a layer of epithelial cells?

Accepted Answer

Tight junctions

Question 2

Plasmodesmata in plant cells serve a similar function to which type of junction in animal cells?

Accepted Answer

Gap junctions

Question 3

A researcher observes that a signaling molecule binds to a receptor on the cell surface, causing a shape change and activating a G protein. Which type of receptor is most likely involved?

Accepted Answer

G protein-coupled receptor (GPCR)

Question 4

Which of the following best describes the role of protein kinases in signal transduction pathways?

Accepted Answer

They transfer phosphate groups from ATP to proteins.

Question 5

A mutation causes a cell to produce a defective protein phosphatase. What is the most likely consequence for the cell’s signaling pathways?

Accepted Answer

Proteins will remain phosphorylated longer, potentially leading to prolonged or inappropriate cellular responses.

Question 6

Which of the following is a second messenger commonly involved in G protein-coupled receptor (GPCR) signaling pathways?

Accepted Answer

cAMP

Question 7

The cholera toxin causes intestinal cells to secrete large amounts of salt and water by modifying a G protein. What is the direct effect of this modification?

Accepted Answer

The G protein is locked in its active form, leading to continuous cAMP production.

Question 8

Which equation correctly represents the conversion of ATP to cAMP by adenylyl cyclase?

Accepted Answer

$$ATP \rightarrow cAMP + PP_i$$

Question 9

Steroid hormones can pass through the plasma membrane and bind to intracellular receptors. What property allows them to do this?

Accepted Answer

They are hydrophobic and nonpolar.

Question 10

A cell receives a death signal that inactivates the Ced-9 protein in the mitochondrial membrane. What is the immediate consequence?

Accepted Answer

The apoptotic pathway is activated, leading to cell death.

Question 11

Which of the following best explains why signal transduction pathways often involve multiple steps?

Accepted Answer

To amplify the signal and provide opportunities for regulation.

Question 12

Which of the following is NOT a function of scaffolding proteins in cell signaling?

Accepted Answer

Terminating the signal by degrading signaling molecules.

Question 13

Which of the following statements about apoptosis is TRUE?

Accepted Answer

Apoptosis packages cell components into vesicles for digestion by scavenger cells.

Question 14

A ligand-gated ion channel receptor opens in response to a signal molecule. What is the most immediate effect?

Accepted Answer

Specific ions, such as $$Na^+ or$$ $$Ca^{2+}$$, flow through the channel.

Question 15

Which of the following best describes paracrine signaling?

Accepted Answer

A cell releases local regulators that affect nearby target cells.

Question 16

Which process is responsible for rapidly removing phosphate groups from proteins in a signaling pathway?

Accepted Answer

Dephosphorylation

Question 17

A cell’s response to a signal can be regulated in several ways. Which of the following is NOT one of the four aspects of signal regulation?

Accepted Answer

Permanent activation of the receptor

Question 18

Which of the following is most likely to occur if the concentration of an external signaling molecule falls?

Accepted Answer

Fewer receptors will be bound, and bound receptors will revert to an inactive state.

Question 19

Which of the following is a real-world example of a disease caused by disruption of cell signaling pathways?

Accepted Answer

Cholera

Question 20

Which of the following best describes the function of receptor tyrosine kinases (RTKs)?

Accepted Answer

They catalyze the transfer of phosphate groups from ATP to other proteins.

Cell Communication and Signaling in Multicellular Organisms

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