Question 1

Which of the following statements best describes the mechanism by which the ced-9 protein in the nematode C. elegans prevents apoptosis in normal cells?

Accepted Answer

A)   Active ced-9 prevents activation of the caspase activity of ced-3.
B)   Ced-9 remains inactive until it is stimulated by ced-3 and other caspases.
C)   Ced-9 is cleaved to produce the active ced-3 caspase.
D)   Ced-9 inhibits the cell membrane receptor for the death-signaling molecule.E) A) and B)
F) None of the above

Question 2

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

Accepted Answer

A)   receptor tyrosine kinase
B)   G protein-coupled receptor
C)   ligand-gated ion channel
D)   steroid receptorE) A) and B)
F) A) and C)

Question 3

Which of the following statements best describes the effect of a mutation that knocks out the GTPase activity of a G protein?

Accepted Answer

A)   The concentration of available GTP would decrease.
B)   The number of G proteins in the cell would increase.
C)   The G protein would be inactivated by a G protein-coupled receptor/signal molecule complex.
D)   The G protein would always be active.E) C) and D)
F) B) and C)

Question 4

Not all intercellular signals require transduction. Which one of the following signals may be processed without transduction?

Accepted Answer

A)   a lipid-soluble signal
B)   a signal that is weakly bound to a nucleotide
C)   a signal that binds to a receptor in the cell membrane
D)   a signal that binds to the extracellular matrixE) None of the above
F) A) and B)

Question 5

Which of the following responses is stimulated by cell signaling the formation of biofilms?

Accepted Answer

A)   formation of mating complexes
B)   aggregation of bacteria
C)   secretion of substances that inhibit growth of foreign bacteria
D)   inhibition of quorum sensingE) All of the above
F) A) and B)

Question 6

Viagra causes dilation of blood vessels and increased blood flow to the penis, which helps to maintain an erection. Viagra acts by inhibiting which of the following events?

Accepted Answer

A)   hydrolysis of cGMP to GMP
B)   hydrolysis of GTP to GDP
C)   dephosphorylation of cGMP
D)   formation of cGMP from GTPE) B) and C)
F) A) and D)

Question 7

What role do phosphatases play in signal transduction pathways?

Accepted Answer

A)   They transfer a phosphate group from one protein in the pathway to the next molecule in the series.
B)   They activate protein kinases by phosphorylation.
C)   They amplify the second messenger cAMP.
D)   They inactivate protein kinases to turn off signal transduction.E) B) and C)
F) None of the above

Question 8

Binding of epinephrine to its receptor results in which of the following events?

Accepted Answer

A)   Stimulation of glycogen synthesis.
B)   A decrease in blood glucose levels.
C)   Inhibition of glycogen phosphorylase.
D)   Elevation of cytosolic concentrations of cyclic AMP.E) C) and D)
F) B) and D)

Question 9

Which of the following conditions is required for a target organ to respond to a particular hormone?

Accepted Answer

A)   Cells in the target organ must modify their plasma membranes to allow the hormone to enter the cytoplasm.
B)   The target organ must be the same as the organ that produced the hormone.
C)   The target organ must have the opposite mating type of the organ that produced the hormone.
D)   The target organ must have receptors that recognize and bind the hormone molecule.E) B) and C)
F) A) and D)

Question 10

Some cases of human melanoma have been shown to result from inhibition of apoptosis in these cells. The human analogue of which of the following defects in C. elegans could cause these cancers?

Accepted Answer

A)   A ced-9 protein that is always inactive.
B)   A ced-3 protein that is always inactive.
C)   A ced-4 protein that is always active.
D)   A death-signaling molecule receptor that is always active.E) A) and C)
F) None of the above

Question 11

Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytosol during signal transduction?

Accepted Answer

A)   tyrosine
B)   glycine and histidine
C)   serine and threonine
D)   glycine and glutamic acidE) A) and B)
F) A) and C)

Question 12

Which of the following statements best describes the function of the α factor secreted by yeast cells?

Accepted Answer

A)   It binds to receptors on α cells to stimulate mating between α cells.
B)   It binds to receptors on α cells to stimulate mating between a cells and α cells.
C)   It binds to receptors on a cells to stimulate mating between a cells.
D)   It diffuses through the membranes of a cells, binds to DNA and initiates transcription of a factor genes.E) A) and B)
F) A) and C)

Question 13

A loss of function of Apaf1, the human homologue of ced-4 in nematodes, is most likely to result in which of the following?

Accepted Answer

A)   activation of a developmental pathway found in the nematode but not in humans
B)   a form of cancer in which normal apoptosis fails
C)   excess activation of the human analog of the ced-3 protease
D)   extensive tissue damage due to excess apoptosisE) B) and D)
F) A) and D)

Question 14

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.

Accepted Answer

A)   cAMP
B)   G protein
C)   GTP
D)   adenylyl cyclaseE) B) and D)
F) B) and C)

Question 15

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of which of the following molecules?

Accepted Answer

A)   phosphorylated proteins
B)   cAMP
C)   adenylyl cyclase
D)   activated G proteinsE) A) and B)
F) A) and C)

Question 16

Which of the following signal transduction proteins typically functions by forming dimers after binding to a signal molecule?

Accepted Answer

A)   G protein-coupled receptors
B)   ligand-gated ion channels
C)   steroid receptors
D)   receptor tyrosine kinasesE) All of the above
F) A) and B)

Question 17

Which of the following statements best describes the mechanism by which testosterone functions inside a cell?

Accepted Answer

A)   It acts as a signal receptor that activates tyrosine kinases.
B)   It binds with a receptor protein that enters the nucleus and activates expression of specific genes.
C)   It acts as a steroid signal receptor that activates ion channel proteins in the plasma membrane.
D)   It coordinates a phosphorylation cascade that reduces spermatogenesis.E) None of the above
F) C) and D)

Question 18

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would you expect to find the carboxyl terminus of the protein?

Accepted Answer

A)   at the exterior surface of the plasma membrane
B)   at the cytosolic surface of the plasma membrane
C)   covalently bound to the amino end of the protein
D)   embedded in the phospholipid bilayer of the membraneE) A) and B)
F) A) and C)

Question 19

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because ________.

Accepted Answer

A)   only target cells retain the appropriate DNA segments
B)   intracellular receptors are present only in target cells
C)   only target cells have enzymes that break down aldosterone
D)   only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes onE) None of the above
F) A) and C)

Question 20

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would a coupled G protein most likely interact with this receptor?

Accepted Answer

A)   at the amino end
B)   at the carboxyl end
C)   along the exterior margin
D)   at the loop between helix 5 and helix 6E) B) and C)
F) C) and D)

Exam 9: Cellular Signaling

Which of the following signal transduction proteins typically functions by forming dimers after binding to a signal molecule?

Correct AnswerverifiedShow Answer

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because ________.

Correct AnswerverifiedShow Answer

Which of the following statements best describes the effect of a mutation that knocks out the GTPase activity of a G protein?

Correct AnswerverifiedShow Answer

What role do phosphatases play in signal transduction pathways?

Correct AnswerverifiedShow Answer

Viagra causes dilation of blood vessels and increased blood flow to the penis, which helps to maintain an erection. Viagra acts by inhibiting which of the following events?

Correct AnswerverifiedShow Answer

A loss of function of Apaf1, the human homologue of ced-4 in nematodes, is most likely to result in which of the following?

Correct AnswerverifiedShow Answer

Which of the following responses is stimulated by cell signaling the formation of biofilms?

Correct AnswerverifiedShow Answer

Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytosol during signal transduction?

Correct AnswerverifiedShow Answer

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

Correct AnswerverifiedShow Answer

Not all intercellular signals require transduction. Which one of the following signals may be processed without transduction?

Correct AnswerverifiedShow Answer

Which of the following statements best describes the function of the α factor secreted by yeast cells?

Correct AnswerverifiedShow Answer

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would a coupled G protein most likely interact with this receptor?

Correct AnswerverifiedShow Answer

Which of the following statements best describes the mechanism by which the ced-9 protein in the nematode C. elegans prevents apoptosis in normal cells?

Correct AnswerverifiedShow Answer

Some cases of human melanoma have been shown to result from inhibition of apoptosis in these cells. The human analogue of which of the following defects in C. elegans could cause these cancers?

Correct AnswerverifiedShow Answer

Which of the following conditions is required for a target organ to respond to a particular hormone?

Correct AnswerverifiedShow Answer

Binding of epinephrine to its receptor results in which of the following events?

Correct AnswerverifiedShow Answer

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would you expect to find the carboxyl terminus of the protein?

Correct AnswerverifiedShow Answer

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of which of the following molecules?

Correct AnswerverifiedShow Answer

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.

Correct AnswerverifiedShow Answer

Which of the following statements best describes the mechanism by which testosterone functions inside a cell?

Correct AnswerverifiedShow Answer

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