This set of Molecular Endocrinology Multiple Choice Questions & Answers (MCQs) focuses on “Downstream Signaling Pathways, Off Signals Termination of Hormone Action”.
1. Which among the following are the most important SH2 domain-containing proteins?
a) PI3K and GRB2
b) PI3K and GRB3
c) PI5K and GRB2
d) PI5K and GRB3
View Answer
Explanation: PI3K and GRB2 are two of the most important SH2 protein-containing domains. Many downstream signaling pathways are caused by the binding of SH2 domains. SH2 domains allow phosphorylated tyrosine residues on other proteins to dock to proteins containing those domains.
2. Which among the following is the classic isoform of the regulatory subunit of the catalytic PI3K subunit?
a) p87
b) p85
c) p89
d) p81
View Answer
Explanation: P13 K have one regulatory subunit and one catalytic subunit. The regulatory subunit exists in its isoform p85 with SH2 domains. Phosphatidylinositol 3-kinases (P13K), are a set of enzymes that respond to various hormones like insulin and they have major role in various cell signalling pathways like that of cancer.
3. Which among the following downstream kinases are triggered by the activation of PI3K?
a) Phosphatidylcholine-dependent kinases 1 and 2
b) Phosphoethonalamine-dependent kinases 1 and 2
c) Phosphoinositide-dependent kinases 1 and 2
d) phosphatidylethanolamine-dependent kinases 1 and 2
View Answer
Explanation: PI3K activation causes the activation of a downstream kinase cascade, starting with phosphoinositide-dependent kinases 1 and 2. These kinases phosphorylate and activate numerous kinases of the downstream protein, including protein kinase B and a typical protein kinase C isoform.
4. IRS proteins act as docking proteins that bind proteins containing the SH2 domain.
a) True
b) False
View Answer
Explanation: Many substrates contain several phosphorylation sites for tyrosine, many of which lead to SH2 domain consensus sequences in essential signaling molecules. IRS proteins act as docking proteins that bind proteins containing the SH2 domain.
5. In insulin/IGF1 signaling, GAB1 acts as a special intermediate.
a) True
b) False
View Answer
Explanation: It has been proposed that in insulin/IGF1 signaling, GAB1 acts as a special intermediate. This is used for early gene expression activation and mitogenesis stimulation without specific phosphorylation of tyrosine.
6. Which among the following is the inhibitor of PI3K?
a) DNP
b) Wortmannin
c) Acrylamide
d) Acetylcholine
View Answer
Explanation: The PI3K inhibitor, wortmannin, blocks the metabolic activities of insulin. Similarly, overexpression of dominant negative mutants of the PI3K regulatory subunit p85 also inhibits the metabolic actions of insulin.
7. The phosphorylation of which protein provide the second parallel pathway to trigger the activation of insulin?
a) CBL
b) Globulin
c) Helicases
d) JAK
View Answer
Explanation: The Cbl/CAP dependent signalling pathway in adipocytes has been involved in the regulation of glucose uptake stimulated by insulin. In order to activate the metabolic activities of insulin, a second parallel route could be needed. This includes the phosphorylation of CBL by tyrosine.
8. Which among the following is a short adaptor molecule that contains an SH2 domain capable of binding to pTyr residue?
a) CBL1
b) CBL3
c) GRB3
d) GRB2
View Answer
Explanation: GRB2 is a short adaptor molecule containing a domain of SH2 capable of binding to residues of pTyr. This binds to a variety of signaling molecules, including IRS1 and SHC. Growth factor receptor-bound protein 2 is an adaptor protein involved in signal transduction/cell communication.
9. The SH3 domain of GRB2 binds to which amino acid containing sequence in mammalian homolog of drosophila?
a) Proline
b) Lysine
c) Valine
d) Arginine
View Answer
Explanation: GRB2’s SH2 domain is flanked by two SH3 domains. It binds to proline-containing sequences in a Drosophila son-of-sevenless which is a mammalian homolog. The SH3 domains of Grb2 are attached to the proline-rich carboxy-terminal tail of mSos1 in rodent fibroblasts, a protein homologous to Drosophila.
10. Which among the following is a small G protein that is activated by the guanine nucleotide exchange factor in mammalian homolog of drosophila?
a) GRT
b) RAS
c) CBL
d) LPO
View Answer
Explanation: The Ras protein, which is a Ras gene-encoded low-molecular-weight GDP/GTP-binding guanine triphosphatase, plays a critical role in cell growth and differentiation signal transduction. RAS can be triggered by the guanine nucleotide exchange factor in mammalian drosophila homologues. In intracellular signaling pathways, this is a small G protein that plays a significant role.
11. How do insulin binding accelerates the rate of receptor degradation?
a) Receptor-Mediated Endocytosis
b) Receptor-Mediated Exocytosis
c) Ligand-Mediated Endocytosis
d) Ligand-Mediated Exocytosis
View Answer
Explanation: The binding of insulin to its receptor causes receptor endocytosis. Although most internalized receptors are recycled into the plasma membrane, others are transferred to damaged lysosomes. As a result, the rate of receptor degradation is increased by insulin binding.
12. What factor of the endosome promotes dissociation of insulin from its receptor?
a) Acidic pH
b) Basic pH
c) High Temperature
d) Low temperature
View Answer
Explanation: Endosomes contain pumps of protons which acidify the lumen. Dissociation of insulin from its receptor is facilitated by the acidic pH within the endosome. Then, insulin is gradually transported to the lysosome for degradation.
13. Which enzyme catalyzes the dephosphorylation of tyrosine residues in receptor tyrosine kinases?
a) Protein tyrosine phosphatases (PTPs)
b) Protein kinases
c) Protein lipases
d) Protein deacetylases
View Answer
Explanation: Phosphorylation of proteins is a complex process. The phosphorylation of tyrosine residues is catalyzed by tyrosine kinases, but to eliminate the phosphates (dephosphorylation), there are also protein tyrosine phosphatases (PTPs).
14. Absence of which among the following phosphatases is associated with increased insulin sensitivity?
a) PTP1B
b) PTP2B
c) PTP1A
d) PTP2B
View Answer
Explanation: Studies with knockout mice have shown that PTP1B absence is associated with improved susceptibility to insulin. This absorption defends against weight gain. Sensitivity to insulin refers to how receptive the cells of the body are to insulin in response.
15. What is the role of Ser/Thr phosphorylation in the action of tyrosine kinases?
a) Inhibits
b) Activates
c) Reduces
d) Helping mechanism
View Answer
Explanation: Most receptor tyrosine kinases are substrates for phosphorylation by Ser/Thr-specific protein kinases, including the insulin receptor. Phosphorylation of Ser/Thr tends to suppress tyrosine kinase activity.
Sanfoundry Global Education & Learning Series – Molecular Endocrinology.
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