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Exam 9: Cell Communication

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Question 21

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Using a specific chemical, a cell biologist has blocked one type of channel-linked receptor in a lab rat's liver tissue.What was the likely mechanism of the chemical she used?

A) The chemical prohibits binding of a ligand to the receptor.
B) The chemical prohibits ions from entering the cell via active transport.
C) The chemical causes ions to move in the opposite direction of the ion gradient.
D) The chemical prohibits second messenger signaling.

E) A) and B)
F) None of the above

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Question 22

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Leptin is a circulating hormone that is produced by fat cells and plays a role in body metabolism and obesity.It normally binds to receptors in the brain and inhibits appetite.Studies have demonstrated that when obese mice that are leptin deficient are injected with leptin they quickly lose their excess weight.Interestingly, however, many overweight people have high levels of leptin in their bloodstream.Why do you think that the high levels of leptin in obese individuals are insufficient to curb their appetite?

A) Paracrine signaling may be disrupted in obese people with high levels of leptin.
B) Obese people who have high levels of leptin may have a leptin receptor with decreased sensitivity.
C) The form of leptin released by obese people may lack protein kinase activity.
D) In obese people with high levels of leptin, the leptin is a non-functional second messenger.

E) A) and B)
F) A) and C)

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Question 23

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What signaling pathway commonly makes use of a G protein to transduce the signal?

The function of adenylyl cyclase is to:

When bound to ligand, this type of receptor changes conformation to allow ions to move down their concentration gradient across the membrane:

Your research project involves the characterization of a particular signal transduction pathway.Specifically, you have been studying a receptor tyrosine kinase and protein X, which initiates downstream events.You are certain that protein X is part of the signal transduction pathway, but have been unable to identify a direct protein-protein interaction between the receptor tyrosine kinase and the protein X.What should you do next in your attempt to identify a link between the receptor tyrosine kinase and protein X?

A researcher is working to generate a new cancer drug.Thus far, he has identified a compound that can reduce the size of tumors in the lung.However, in order for the drug to work, the lung tumor has to be small.In addition, the tumor cannot have metastasized (spread to other areas of the body) .Furthermore, he knows that the drug acts to prohibit the signaling from one tumor cell to another tumor cell.Given the above information, this new drug prohibits:

What enzyme phosphorylates MAP kinase kinase?

In synaptic signaling, neurotransmitters are released into a space that is referred to as a:

You have identified a novel cytoplasmic protein.Through sequence analysis you are able to identify the presence of a number of serine/threonine phosphorylation motifs.Based on these data, you hypothesize that this protein may be a substrate for what kind of enzyme?

What property defines most ligands for intracellular receptors?

In the nitric oxide signaling pathway, nitric oxide activates an enzyme that can convert many molecules of GTP into molecules of cGMP.cGMP is a small molecule that can diffuse through the cytoplasm and bind to an enzyme called protein kinase G (PKG) .Binding of cGMP to PKG leads to a change in the confirmation of PKG that leads to its activation.What type of signaling molecule is cGMP?

Growth of new blood vessels is stimulated by vascular endothelial growth factor (VEGF) .This ligand binds to the VEGF receptor, which leads to the dimerization and autophosphorylation of this receptor on cytoplasmic tyrosines.What type of receptor is the VEGF receptor?

The cell surface receptors that can act only indirectly on plasma membrane-bound enzymes or ion channels are called:

Vasopressin is a hormone that is primarily released when the body is low on water.Release of vasopressin causes the kidneys to conserve water by concentrating urine and decreasing urine output.However, vasopressin also has additional functions in other tissues such as the brain and blood vessels, which are not directly involved in urine production.How could it be possible for vasopressin to trigger different responses in different tissues?

What type of receptor is not an enzyme, but is directly associated with an enzyme that can hydrolyze GTP?

What is similar about G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) ?

You are interested in developing an inhibitor for the estrogen receptor.You have identified a molecule that is small and hydrophilic.In a test tube, this inhibitor binds tightly to the estrogen receptor, and inhibits the interaction of the receptor with estrogen.Do you think that this molecule will be an effective inhibitor of the estrogen receptor in cells?

If the effector protein phospholipase C failed to cleave phosphatidylinositol-4,5-bisphosphate (PIP₂) , the action of what enzyme would be affected?

One cell sends second messengers to another cell through gap junctions.What type of signaling would this be considered?