Mini 1 Part 2 Cell Signaling
Mini practice quiz
- 1.
The second messenger cAMP induces its effects by binding to the regulatory subunits of protein kinase A. What is the immediate target of the second messenger IP3?
- A.
A calcium channel in the ER membrane
- B.
Phospholipase C
- C.
Protein kinase C
- D.
A nuclear DNA-binding protein
- E.
Calmodulin
Correct Answer
A. A calcium channel in the ER membraneExplanation
The immediate target of the second messenger IP3 is a calcium channel in the ER membrane. IP3 binds to specific receptors on the ER membrane, causing the release of calcium ions from the ER into the cytoplasm. This increase in cytoplasmic calcium levels then triggers various cellular responses, such as muscle contraction, secretion, and gene expression. Therefore, the correct answer is a calcium channel in the ER membrane.Rate this question:
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- 2.
Glucagon can induce gene transcription in the liver. How?
- A.
It is translocated to the nucleus where it binds to response elements in the regulatory sequences of the genes.
- B.
It triggers cAMP formation, and cAMP activates genes by binding to the catabolite activator protein
- C.
It releases calcium from the ER, which activates protein kinase C in the nucleus
- D.
It causes phosphorylation of nuclear transcription factors by protein kinase A
- E.
It induces the formation of the second messenger IP3, which activates transcription by binding to nuclear transcription factors
Correct Answer
D. It causes phosphorylation of nuclear transcription factors by protein kinase AExplanation
Glucagon activates the protein kinase A (PKA) pathway, which leads to the phosphorylation of nuclear transcription factors. This phosphorylation allows the transcription factors to bind to specific regulatory sequences in the genes' regulatory regions, thereby inducing gene transcription in the liver.Rate this question:
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- 3.
What is the difference between nicotinic and muscarinic acetylcholine receptors?
- A.
Nicotinic: has guanylate cyclase activity; muscarinic: ion channel
- B.
Nicotinic: ion channel; muscarinic: coupled to G-proteins
- C.
Nicotinic: coupled to G-proteins; muscarinic: has adenylate cyclase activity
- D.
Nicotinic: coupled to G-proteins; muscarinic: ion channel
- E.
Nicotinic: ion channel; muscarinic: has tyrosine-specific protein kinase activity
Correct Answer
B. Nicotinic: ion channel; muscarinic: coupled to G-proteinsExplanation
Nicotinic acetylcholine receptors are ion channels, meaning they allow the flow of ions across the cell membrane when activated by acetylcholine. On the other hand, muscarinic acetylcholine receptors are coupled to G-proteins, which means they initiate intracellular signaling pathways when activated by acetylcholine. Therefore, the correct answer states that nicotinic receptors are ion channels, while muscarinic receptors are coupled to G-proteins.Rate this question:
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- 4.
Inositol 1,4,5-trisphosphate (IP3) is a second messenger of many hormones. To form this second messenger, you need the enzyme:
- A.
Phosphodiesterase
- B.
Protein kinase C
- C.
Protein kinase B
- D.
Phospholipase C
- E.
Ras
Correct Answer
D. Phospholipase CExplanation
Phospholipase C is the correct answer because it is the enzyme responsible for cleaving phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 then acts as a second messenger by binding to IP3 receptors on the endoplasmic reticulum, leading to the release of calcium ions into the cytoplasm. This calcium release triggers various cellular responses, including hormone secretion, muscle contraction, and gene expression. Therefore, without the action of phospholipase C, the formation of IP3, and subsequent cellular responses mediated by IP3, would not occur.Rate this question:
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- 5.
CAMP stimulates hormone production and cell proliferation in many endocrine tissues including the thyroid gland. Therefore a type of somatic mutation that is most likely to lead to the formation of a hormone-overproducing benign tumor in the thyroid gland (a "toxic nodule") is one that causes:
- A.
Inability of the Gs protein to hydrolyze its bound GTP
- B.
Inability of the Gi protein to hydrolyze its bound GTP
- C.
Inability of the protein kinase A regulatory subunits to respond to cAMP
- D.
Absence of the CREB (cyclic AMP response element binding) protein
- E.
Degeneration of the TSH-producing thyrotrophs in the anterior pituitary gland
Correct Answer
A. Inability of the Gs protein to hydrolyze its bound GTPExplanation
The Gs protein is responsible for activating adenylate cyclase, which in turn increases the production of cAMP. If the Gs protein is unable to hydrolyze its bound GTP, it will remain in its active state, continuously stimulating adenylate cyclase and leading to excessive production of cAMP. This excessive cAMP production can stimulate hormone production and cell proliferation in the thyroid gland, ultimately resulting in the formation of a hormone-overproducing benign tumor. Therefore, the inability of the Gs protein to hydrolyze its bound GTP is the most likely somatic mutation to cause the formation of a toxic nodule in the thyroid gland.Rate this question:
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- 6.
There is much overlap of the intracellular signaling cascades of growth factors such as EGF (epidermal growth factor) and PDGF (platelet-derived growth factor) with those triggered by:
- A.
Neurotransmitters
- B.
Hormones acting through cGMP
- C.
Steroid hormones
- D.
Insulin
- E.
Hormones that are coupled to heterotrimeric G proteins
Correct Answer
D. InsulinExplanation
Insulin is known to activate several intracellular signaling pathways, including the PI3K/Akt pathway and the MAPK pathway. These pathways are also activated by growth factors like EGF and PDGF. Therefore, there is significant overlap in the intracellular signaling cascades triggered by insulin and these growth factors.Rate this question:
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- 7.
Many cytoplasmic enzymes become activated in response to an elevated calcium concentration. In most cases these effects are mediated by the protein:
- A.
Calmodulin
- B.
Phospholipase A2
- C.
Troponin
- D.
Calsequestrin
- E.
Calcineurin
Correct Answer
A. CalmodulinExplanation
Calmodulin is a protein that plays a crucial role in regulating the activity of many cytoplasmic enzymes in response to an elevated calcium concentration. It acts as a calcium-binding protein and undergoes a conformational change when it binds to calcium ions. This conformational change allows calmodulin to interact with and activate various enzymes, such as protein kinases, phosphatases, and phosphodiesterases. By binding to calmodulin, these enzymes are able to carry out their specific functions in response to changes in intracellular calcium levels. Therefore, calmodulin serves as a key mediator in the activation of cytoplasmic enzymes in the presence of elevated calcium.Rate this question:
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- 8.
One important feature of the insulin receptor is:
- A.
It phosphorylates proteins on tyrosine side chains
- B.
It is coupled to the Gi protein
- C.
It is coupled to the Gq protein
- D.
It has guanylate cyclase activity
- E.
It mediates many of its effects through the production of nitric oxide (NO)
Correct Answer
A. It phosphorylates proteins on tyrosine side chainsExplanation
The insulin receptor is known for its ability to phosphorylate proteins on tyrosine side chains. This phosphorylation process plays a crucial role in insulin signaling and helps regulate various cellular processes such as glucose uptake, glycogen synthesis, and protein synthesis. By phosphorylating specific proteins, the insulin receptor initiates a cascade of signaling events that ultimately result in the cellular responses to insulin.Rate this question:
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- 9.
A linkage study has found that there is a gene for test taking skill in a particular region on the long arm of chromosome 4. A search of the human genome sequence shows that this chromosomal region contains a gene of unknown function. This gene encodes a protein that has not only a signal sequence, but also seven hydrophobic sequences, each about 20 amino acid residues long. The gene product is most likely:
- A.
A voltage-gated ion channel
- B.
A ligand-gated ion channel
- C.
A cytoplasmic protein kinase
- D.
A hormone receptor that is linked to G-proteins
- E.
A hormone receptor with a tyrosine-specific protein kinase activity
Correct Answer
D. A hormone receptor that is linked to G-proteinsExplanation
The correct answer is a hormone receptor that is linked to G-proteins. This is because the gene in question encodes a protein with a signal sequence, suggesting that it is secreted from the cell. Additionally, the presence of hydrophobic sequences indicates that the protein is likely embedded in the cell membrane. Hormone receptors are often embedded in the cell membrane and are linked to G-proteins, which are involved in signal transduction pathways. Therefore, it is likely that the gene product in this case is a hormone receptor that is linked to G-proteins.Rate this question:
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- 10.
Some hormones act by triggering the release of calcium from the endoplasmic reticulum. These hormones can regulate gene expression, usually by:
- A.
The binding of calcium to transcription factors, which in turn bind to promoters and enhancers of genes
- B.
The activation of calmodulin-regulated protein kinases that phosphorylate nuclear transcription factors
- C.
The direct binding of calcium to the DNA double helix
- D.
The methylation of DNA in the promoters and enhancers of genes by a calcium-dependent enzyme
- E.
The binding of calcium to mRNA, which stabilizes the RNA against the action of RNA-degrading enzymes
Correct Answer
B. The activation of calmodulin-regulated protein kinases that phosphorylate nuclear transcription factorsExplanation
Some hormones trigger the release of calcium from the endoplasmic reticulum, which then activates calmodulin-regulated protein kinases. These protein kinases phosphorylate nuclear transcription factors, which in turn regulate gene expression by binding to promoters and enhancers of genes. This process allows for the control of gene expression in response to hormonal signals.Rate this question:
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- 11.
You work as research director for a pharmaceutical company. One of your tasks is the development of new anti-hypertensive (blood pressure lowering) drugs. Of the following, the most promising drug would be one that:
- A.
Inhibits the endothelial nitric oxide synthase
- B.
Opens voltage-gated calcium channels in the plasma membrane of vascular smooth muscle cells
- C.
Blocks voltage-gated calcium channels in the plasma membrane of endothelial cells but not vascular smooth muscle cells
- D.
. Inhibits the Gs protein in vascular smooth muscle cells
- E.
Prevents the degradation of cAMP in vascular smooth muscle cells but not other cells in the body
Correct Answer
E. Prevents the degradation of cAMP in vascular smooth muscle cells but not other cells in the bodyExplanation
Preventing the degradation of cAMP in vascular smooth muscle cells would lead to an increase in the levels of cAMP, which would result in relaxation of the smooth muscles in blood vessels. This would ultimately lead to vasodilation and a decrease in blood pressure. By specifically targeting vascular smooth muscle cells and not other cells in the body, the drug would have a more targeted effect on blood pressure regulation.Rate this question:
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- 12.
The actions of insulin are initiated by:
- A.
Phosphorylation of the insulin receptor on tyrosine side chains
- B.
Stimulation of cAMP synthesis through a G-protein
- C.
Inhibition of cAMP synthesis through a G-protein
- D.
Formation of IP3 and DAG
- E.
Activation of a guanylate cyclase
Correct Answer
A. Phosphorylation of the insulin receptor on tyrosine side chainsExplanation
Insulin initiates its actions by phosphorylating the insulin receptor on tyrosine side chains. This phosphorylation activates the receptor, leading to a cascade of intracellular signaling events that regulate glucose uptake, glycogen synthesis, and protein synthesis. Phosphorylation of the insulin receptor on tyrosine side chains is a critical step in insulin signaling and is necessary for the downstream effects of insulin on cellular metabolism and growth.Rate this question:
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- 13.
A patient is found to have a small benign tumor in the thyroid gland that overproduces thyroid hormones. The somatic mutation that is most likely to cause this tumor is one that
- A.
Causes the pituitary gland to overproduce TSH
- B.
Prevents hydrolysis of bound GTP by the Gs protein
- C.
Prevents binding of TSH to the TSH receptor
- D.
Prevents the activation of phospholipase C by a G-protein
- E.
Prevents the activation of protein kinase A
Correct Answer
B. Prevents hydrolysis of bound GTP by the Gs proteinExplanation
The correct answer is "prevents hydrolysis of bound GTP by the Gs protein." This mutation would lead to a constitutively active Gs protein, which would result in continuous activation of adenylyl cyclase and increased production of cyclic AMP (cAMP). Increased cAMP levels would then stimulate the thyroid gland to overproduce thyroid hormones.Rate this question:
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- 14.
Growth factors and insulin can regulate gene expression. Which mechanism is most likely to contribute to this effect?
- A.
Dephosphorylation of transcription factors by the protein phosphatase calmodulin
- B.
Binding of the Ras protein to the promoters and enhancers of genes
- C.
Phosphorylation of transcription factors by MAP kinases
- D.
Phosphorylation of a catabolite activator protein in the nucleus
- E.
Phosphorylation of the CREB protein on tyrosine side chains
Correct Answer
C. Phosphorylation of transcription factors by MAP kinasesExplanation
MAP kinases are a family of protein kinases that are involved in various cellular processes, including gene expression. Phosphorylation of transcription factors by MAP kinases can regulate their activity and ability to bind to DNA, thereby influencing gene expression. This phosphorylation event can be triggered by growth factors and insulin, which can activate the MAP kinase signaling pathway. Therefore, the phosphorylation of transcription factors by MAP kinases is the most likely mechanism to contribute to the regulation of gene expression by growth factors and insulin.Rate this question:
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- 15.
Many cytoplasmic enzymes become activated in response to an elevated calcium concentration. In most cases these effects are mediated by the protein
- A.
Calmodulin
- B.
Phospholipase A2
- C.
troponin
- D.
Calsequestrin
- E.
Calcineurin
Correct Answer
A. CalmodulinExplanation
Calmodulin is a protein that plays a crucial role in regulating various cellular processes in response to changes in calcium concentration. When calcium levels rise, calmodulin binds to calcium ions and undergoes a conformational change, allowing it to activate or modulate the activity of target enzymes. This activation of cytoplasmic enzymes by calmodulin helps to regulate processes such as muscle contraction, cell signaling, and gene expression. Therefore, the correct answer is calmodulin.Rate this question:
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