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45 Cards in this Set
- Front
- Back
1. The protein Sonic Hedgehog (SHH) plays a role in specifying the identity of digits (such as fingers and toes) in mammals. Several digits arise directly from cells that both express and respond to secreted SHH. What type of signaling would this be considered? |
E. Autocrine |
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2. One cell sends second messengers to another cell through gap junctions. What type of signaling would this be considered? |
A. Direct contact |
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3. In synaptic signaling, neurotransmitters are released into a space that is referred to as a: |
A. chemical synapse. |
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4. In response to injury, cell fragments called platelets get activated to induce clotting. Activated platelets release factors that can in turn bind to specific membrane receptors on nearby cells. What type of signaling would this be considered? |
B. Paracrine |
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5. 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: |
C. paracrine signaling between tumor cells. |
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6. 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. |
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7. 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? |
B. Obese people who have high levels of leptin may have a leptin receptor with decreased sensitivity. |
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8. 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? |
A. Vasopressin can bind to, and act on, different receptor subtypes, leading to different cellular responses in different tissues. |
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9. Addison's disease is a disorder that results from a reduction in production of glucocorticoids and mineralocorticoids. Individuals with Addison's disease suffer from a variety of systemic symptoms including: muscle weakness, fever, issues with the gastrointestinal tract, and increased tanning. Considering this information, what type of signaling do you think that glucocorticoids and mineralocorticoids stimulate? |
C. Endocrine |
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10. What is the function of a protein kinase? |
D. To add phosphate groups onto proteins |
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11. 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? |
A. A protein kinase |
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12. You have identified a molecule, molecule X, that can bind to the ATP binding site of a specific protein kinase, and prevent ATP binding. You are conducting a kinase assay using this protein kinase and a known substrate of this kinase, and have set up the reaction using the proper conditions and co-factors to allow for optimal protein kinase activity. If you add molecule X to the reaction, what do you predict will be the outcome? |
B. Less phosphorylation of the substrate will be seen in the presence of molecule X. |
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13. Why are phosphorylation and dephosphorylation reactions commonly used to regulate signal transduction pathways? |
D. The addition or removal of a phosphate group can expose or hide potential binding sites in proteins or change protein activity |
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14. You are performing an experiment to assay phosphorylation of a substrate by a protein kinase. Based on the data in the table below, what do these experimental results suggest? |
B. The substrate can undergo autophosphorylation. |
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15. These molecules can directly convert extracellular signals into intracellular signals. |
C. Membrane receptors |
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16. When bound to ligand, this type of receptor changes conformation to allow ions to move down their concentration gradient across the membrane: |
A. Channel-linked receptor |
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17. 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? |
B. Enzymatic receptor |
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18. What type of receptor is not an enzyme, but is directly associated with an enzyme that can hydrolyze GTP? |
C. G protein-coupled receptor |
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19. You are planning to perform some protein-protein interaction studies to identify a receptor for a steroid hormone you have been working on. You start by fractionating the cell. What cell fraction would you want to work with to identify the steroid hormone receptor of interest? |
C. The cytoplasmic fraction |
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20. What property defines most ligands for intracellular receptors? |
A. They are lipid-soluble |
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21. 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? |
C. No, because it is hydrophilic. |
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22. Tamoxifen is a drug that is used to treat breast cancer. It inhibits the activities of the estrogen receptor in breast epithelial cells, which are the cells that are relevant to breast cancer. One of the concerns that scientists had during the development of Tamoxifen as a therapy for breast cancer was that other cell types require estrogen signaling for their function. For example, it is known that cells in bone tissue require estrogen signaling. As a result, there was a concern that use of Tamoxifen would lead to bone loss in patients. In reality, however, researchers were surprised to find that Tamoxifen actually led to an increase in bone density in breast cancer patients. At the same time, Tamoxifen did inhibit the activity of the estrogen receptor in breast epithelial cells in these patients. What is the best explanation for this finding? |
B. The estrogen receptor is bound to different coactivators in different tissues. |
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23. A mutation in the DNA-binding domain of a steroid hormone receptor is most likely to affect what aspect of receptor function? |
D. The cellular response to the hormone |
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24. You are having lunch with an elderly friend when suddenly he begins to experience chest pain and tightness. He reaches into his pocket, gets out one of his nitroglycerin tablets and quickly takes it. After the episode passes, your friend asks you how the nitroglycerin helps his angina. You explain that nitroglycerin gets converted by cells to nitric oxide (NO) causing the smooth muscle cells of the blood vessel to relax and increase blood flow to the heart. He pushes you for a more detailed explanation, so you explain further that: |
A. NO activates guanylyl cyclase, which catalyzes the synthesis of cGMP, which acts as an intracellular messenger in a pathway leading to smooth muscle relaxation. |
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25. What is the mechanism by which binding of testosterone to the testosterone receptor leads to upregulated gene transcription? |
C. Binding of testosterone to the testosterone receptor leads to a conformational change that allows the receptor to enter the nucleus where it can bind to DNA and promote gene transcription. |
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26. How are receptor tyrosine kinases and steroid hormone receptors similar? |
D. Both have a site for binding ligand |
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27. Some cancers are caused by the overexpression of receptor tyrosine kinases (RTKs). It is known that RTK signaling pathways commonly stimulate cell division. Why would the overexpression of receptor tyrosine kinases lead to cancer development? |
A. RTKs are activated by dimerization, caused by ligand binding. If there are too many receptors on the cell surface, it is possible that these receptors dimerize in the absence of ligand binding, thus stimulating cell division at inappropriate times. |
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28. What signaling pathway commonly makes use of a G protein to transduce the signal? |
C. Receptor tyrosine kinase pathways |
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29. 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? |
C. Try to identify an adapter protein that can interact with both the receptor and protein X. |
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30. The protein SOS is a guanine nucleotide exchange factor for Ras. SOS helps facilitate the exchange of GDP for GTP. What would be the effect of a mutation that inhibits the interaction between SOS and Ras? |
B. GDP would remain bound to Ras, thereby preventing Ras activation. |
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31. Many receptor tyrosine kinase (RTK) pathways lead to the activation of Ras. To activate Ras, it is necessary to recruit a guanine nucleotide exchange factor to the plasma membrane, because Ras is a membrane associated protein. Guanine nucleotide exchange factors, such as SOS, stimulate the exchange of GDP for GTP. However, SOS cannot bind directly to most RTKs. The protein Grb2 has a domain that can bind to phosphorylated tyrosines, and another domain that can bind to SOS. Therefore, Grb2 can bind to active RTKs and recruit SOS to the plasma membrane. Grb2 is an example of what kind of signaling molecule? |
B. Adapter protein |
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32. Ste5 binds to MAPKKK, MAPKK, and MAPK to organize the kinase cascade. What type of signaling molecule is Ste5? |
A. Scaffold |
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33. Many receptor tyrosine kinase pathways have MAPK as a downstream signaling component. MAPK can phosphorylate target proteins. What type of signaling molecule is MAPK? |
D. Enzyme |
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34. A small number of cell surface receptors can ultimately generate a large intracellular response due to activation of kinase cascades. This is referred to as: |
A. signal amplification. |
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35. What enzyme phosphorylates MAP kinase kinase? |
C. MAP kinase kinase kinase |
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36. The cell surface receptors that can act only indirectly on plasma membrane-bound enzymes or ion channels are called: |
A. G protein-coupled receptors. |
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37. G protein-coupled receptors are the largest family of cell surface receptors. Each receptor passes through the plasma membrane how many times? |
D. Seven times |
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38. 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? |
C. Second messenger |
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39. Some enzymatic receptors and most G protein-coupled receptors transmit the signal into the cytoplasm by utilizing other substances within the cytoplasm that are referred to as: |
C. second messengers. |
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40. A mutation that affects Ca++ binding to calmodulin is most likely to interfere with what aspect of a signal transduction pathway? |
B. The cellular response to the second messenger |
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41. If the effector protein phospholipase C failed to cleave phosphatidylinositol-4,5-bisphosphate (PIP2), the action of what enzyme would be affected? |
D. protein kinase C (PKC) |
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42. What is similar about G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs)? |
B. Both can activate phospholipase C |
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43. The function of adenylyl cyclase is to: |
A. catalyze the conversion of ATP to cAMP. |
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44. What is the difference between Ras and the G proteins bound to G protein coupled receptors (GPCRs)? |
C. Ras is a small G protein and the G proteins bound to GPCRs are not small G proteins. |
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45. What second messenger is directly involved in activating protein kinase C (PKC)? |
A. DAG |