Question 1

Which of the following best describes how lipid-soluble signaling molecules, such as steroid hormones, typically affect target cells?

Accepted Answer

They diffuse through the plasma membrane and bind to intracellular receptors, often resulting in changes in gene expression.

Question 2

A researcher adds a signaling molecule to a culture of animal cells. The molecule cannot cross the plasma membrane. Which of the following must be true for the cells to respond?

Accepted Answer

The cells must have a receptor protein embedded in the plasma membrane that can bind the molecule.

Question 3

Which of the following is a key difference between G-protein-coupled receptors (GPCRs) and enzyme-linked receptors?

Accepted Answer

GPCRs activate G-proteins by exchanging GDP for GTP, while enzyme-linked receptors often phosphorylate themselves and other proteins.

Question 4

In a G-protein-coupled receptor pathway, what event leads to the deactivation of the G-protein?

Accepted Answer

The G-protein hydrolyzes GTP to GDP, causing it to reassociate with the receptor.

Question 5

Which of the following best explains why signal transduction pathways are sensitive to changes in the concentration of signaling molecules?

Accepted Answer

The activity of receptors and downstream components depends on the presence and concentration of the signaling molecule, allowing rapid activation and deactivation.

Question 6

A mutation prevents a receptor tyrosine kinase (RTK) from dimerizing. What is the most likely consequence for the cell?

Accepted Answer

The RTK will not be able to autophosphorylate, and the signal transduction cascade will not be initiated.

Question 7

Which of the following scenarios best illustrates the concept of 'crosstalk' between signaling pathways?

Accepted Answer

A component of one signaling pathway inhibits or stimulates a component of a different pathway, integrating multiple signals.

Question 8

In the context of bacterial quorum sensing, what triggers a coordinated response among the population?

Accepted Answer

The accumulation of signaling molecules to a threshold concentration, indicating high population density.

Question 9

Which of the following is a likely cellular response to a lipid-insoluble signal that binds to a membrane receptor?

Accepted Answer

Activation of a signal transduction cascade that may alter cytoplasmic protein activity or gene expression.

Question 10

A patient is given a drug that inhibits phosphatases in their cells. What is the most likely effect on enzyme-linked receptor signaling pathways?

Accepted Answer

The pathways will remain active longer than normal because kinases will not be dephosphorylated.

Question 11

Which of the following best describes the role of secondary messengers in G-protein-coupled receptor pathways?

Accepted Answer

They amplify the signal inside the cell and help trigger a cellular response.

Question 12

Which of the following is a real-world example of quorum sensing in bacteria?

Accepted Answer

The formation of a biofilm (plaque) on teeth when bacteria reach a certain population density.

Question 13

Which of the following steps occurs first in the activation of a G-protein-coupled receptor pathway?

Accepted Answer

A signal molecule binds to the receptor, causing the G-protein to exchange GDP for GTP.

Question 14

A scientist observes that a certain hormone causes a rapid change in cytoplasmic protein activity but does not alter gene expression. Which type of signal and receptor is most likely involved?

Accepted Answer

Lipid-insoluble signal and membrane-bound receptor.

Question 15

Which of the following equations best represents the hydrolysis of GTP by a G-protein during signal deactivation?

Accepted Answer

$\mathrm{GTP} \rightarrow \mathrm{GDP} + \mathrm{P_i}$

Question 16

In the phosphorylation cascade initiated by an enzyme-linked receptor, what is the main function of kinases?

Accepted Answer

Kinases add phosphate groups to other proteins, amplifying the signal.

Question 17

Which of the following best explains why cells need to deactivate signaling pathways after a response is achieved?

Accepted Answer

To ensure that the response is appropriately regulated and does not persist longer than necessary.

Question 18

Which of the following is a likely outcome if a cell's G-protein remains constitutively active (unable to hydrolyze GTP)?

Accepted Answer

The signaling pathway will remain active, potentially leading to uncontrolled cellular responses.

Question 19

In slime molds, what is the biological significance of quorum sensing?

Accepted Answer

It triggers aggregation and the formation of a multicellular slug when population density is high.

Cell-Cell Interactions and Signaling Pathways (Ch. 11.3–11.4)

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