Notes

Cyclic AMP (cAMP) is an example of a(n):
Select one:
a. second messenger.
b. ligand.
c. effector or target protein.
d. G protein.

Question 2
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In cell communication, which one of the following is a requirement of the responding cell?
Select one:
a. It must be a eukaryotic cell.
b. It must produce signaling molecules.
c. It must have receptor proteins.
d. It must be a prokaryotic cell.

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How does an “activated” receptor transfer information into the cell?
Select one:
a. by altering the ligand-binding site of the receptor
b. through a conformational change of the receptor
c. by decreased phosphorylation of the receptor
d. by increased translation of the receptor

Question 4
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The ability of a specific tissue or organ to respond to the presence of a hormone is dependent on:
Select one:
a. the location of the tissue or organ with respect to the circulatory path.
b. the membrane potential of the cells of the target organ.
c. the presence of the appropriate receptors on the cells of the target tissue or organ.
d. nothing. All hormones of the body are able to stimulate all cell types because hormones are powerful and nonspecific.

Question 5
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Photorespiration in chloroplasts resembles cellular respiration in mitochondria in that ________.
Select one:
a. carbon dioxide is produced in both pathways
b. NADH is used in both pathways as the source of high-energy electrons
c. they both store energy in the form of ATP
d. both pathways are beneficial to the cell
e. both reactions are exergonic

Question 6
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What causes the inactivation of a G protein?
Select one:
a. The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate.
b. The beta and gamma subunits trigger the hydrolysis of GTP to GDP.
c. A phosphatase removes the inorganic phosphate group from GTP.
d. The inactive receptor catalyzes the replacement of GTP by GDP.

Question 7
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Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors?
Select one:
a. These chemical inhibitors likely enter eukaryotic cells and interfere with components of the signal transduction pathway.
b. These chemical inhibitors likely enter the nucleus and prevent the transcription of the pathway of interest’s target genes.
c. These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.
d. These chemical inhibitors likely interfere with the termination of signaling, so eukaryotic cells can’t process new signals.

Question 8
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Many diseases are the result of a problem with cell signaling. Which of the following diseases best exemplifies this fact?
Select one:
a. cystic fibrosis, which is caused by a mutation in a channel protein, resulting in a buildup of mucus
b. congestive heart failure, which is caused by chronic high blood pressure due to excessive sodium intake
c. a specific type of cancer, which is caused by a truncated receptor that becomes stuck in the activated form.
d. familial hypercholesterolemia (high cholesterol in the blood), which is caused by a decrease in the number of receptors for cholesterol.

Question 9
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Which type of protein adds a phosphate group to another molecule?
Select one:
a. kinase
b. G protein
c. phosphatase
d. phosphorylase

Question 10
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A newly discovered signaling molecule that binds to a G protein−coupled receptor is being studied by using cells maintained in cell culture. Preliminary results show that the binding of this new ligand causes the activation of adenylyl cyclase. In the next part of this study, a non-hydrolyzable version of GTP (a form of GTP that cannot be converted to GDP) is added to the cell culture dishes and is taken up by the cells. Which of the following would you expect to observe?
Select one:
a. increased cAMP, decreased protein kinase A activity
b. decreased cAMP, decreased protein kinase A activity
c. decreased cAMP, increased protein kinase A activity
d. increased cAMP, increased protein kinase A activity

Question 11
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In the context of cell signaling, to what does the term ligand refer?
Select one:
a. a signaling molecule
b. the extracellular domain of a receptor protein
c. the proteins activated as part of a signal transduction pathway
d. a type of gated channel

Question 12
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You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of chicken cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase. Which of the following mutations would you expect to promote uncontrolled cell proliferation?
Select one:
a. a mutation that prevents dimerization of the receptor
b. a mutation that destroys the kinase activity of the receptor
c. a mutation that inactivates the phosphatase that dephosphorylates the activated receptor
d. a mutation that prevents the binding of the normal extracellular signal to the receptor
Feedback

Question 13
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During the signal transduction process, the signal often triggers a signal transduction cascade. For example, an activated receptor activates hundreds of protein A. Each activated protein A activates hundreds of protein B and so on until a cellular response occurs. What purpose does this cascade serve?
Select one:
a. Having several intermediates allows for greater control of the response.
b. The cascade serves to amplify the signal, so one activated receptor can have a significant response.
c. Having a cascade allows the cell to respond to different signals.
d. The cascade makes signaling easier to shut off or terminate.

Question 14
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Cell signaling over a long distance is known as:
Select one:
a. paracrine signaling.
b. endocrine signaling.
c. contact-dependent signaling.
d. autocrine signaling.

Question 15
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How would the signal of a G protein−coupled receptor, without ligand, be affected if you made a G protein that converted GDP to GTP on its own without needing to be activated by the G protein−coupled receptor?
Select one:
a. The signal wouldn’t be affected; there is no ligand, thus no signal.
b. The signal wouldn’t be affected; the ligand would be unable to bind due to the conformational change.
c. The G protein would be active but unable to signal due to the lack of ligand.
d. The G protein would be active and signaling, despite the lack of ligand.

Question 16
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Recall from the text the example of cell communication in Streptococcus pneumoniae: The rate of DNA uptake by pneumococcal cells increases sharply when they are at high density, due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor proteins, how would the rate of DNA uptake be affected when the cells reach high density?
Select one:
a. There would be no change in the rate of DNA uptake.
b. There would be a larger than normal increase in the rate of DNA uptake.
c. There would be a smaller than normal increase in the rate of DNA uptake.
d. There would be a decrease in the rate of DNA uptake.

During photosynthesis, _______________ is reduced to ___________________.
Select one:
a. water; carbon dioxide
b. carbon dioxide; glucose
c. oxygen; water
d. glucose; oxygen
e. carbon dioxide; oxygen

Question 18

Which type of cell-surface receptor undergoes changes in phosphorylation in response to binding of its ligand?
Select one:
a. G protein–coupled receptor
b. receptor kinase
c. ligand-gated ion channel
d. both the G protein–coupled receptor and the receptor kinase
Question 19
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Which of the following statements is true?
Select one:
a. To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol.
b. Extracellular signal molecules that are hydrophilic must bind to a cell- surface receptor so as to signal a target cell to change its behavior.
c. A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.
d. Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule regardless of the cell type.

Question 20

Question text
A researcher has discovered a new ligand that can pass through the cell membrane and bind to a receptor in the nucleus. Which of the following statements is false regarding this ligand?
Select one:
a. This ligand is likely a steroid.
b. This ligand is likely nonpolar.
c. This ligand likely has a similar structure to cholesterol.
d. This ligand likely binds to a transmembrane receptor.
e. This ligand likely plays a role in transcription.