This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cell Signaling and Signal Transduction – Protein-tyrosine Phosphorylation”.
1. The Protein-tyrosine kinases phosphorylate the ______________ residues.
a) adenine
b) cytosine
c) tyrosine
d) chymosin
View Answer
Explanation: The protein-tyrosine kinases are enzymes that add phosphate groups to specific tyrosine residues on the protein substrates. Protein-tyrosine phosphorylation is a mechanism of signal transduction.
2. How many types of protein-tyrosine kinases are there?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: There are 2 types of protein tyrosine kinases – receptor protein-tyrosine kinases and non-receptor or cytoplasmic protein-tyrosine kinases. The mechanism of activation for both is different.
3. The cytoplasmic protein-tyrosine kinases are activated indirectly by the extracellular signals.
a) True
b) False
View Answer
Explanation: The cytoplasmic protein-tyrosine kinases are activated indirectly by the extracellular signals. These kinases control processes such as immune response, cell adhesion and neuronal cell migration.
4. Bringing 2 kinase domains in close contact allows for ___________________
a) trans-autophosphorylation
b) cis-autophosphorylation
c) inactivation of one domain
d) inactivation of both domains
View Answer
Explanation: When two domains of protein-tyrosine kinases come close, it leads to trans-autophosphorylation in which activity of one receptor of the dimer phosphorylates the tyrosine residue of the other.
5. When the levels of glucose drop, alpha-cells in the pancreas secrete ____________________
a) glucose
b) glucagon
c) starch
d) pancreatic fluid
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Explanation: When the glucose levels drop, alpha cells in the pancreas secrete glucagon in an effort to maintain the glucose levels. The glucagon acts through G-protein coupled receptor and stimulates the breakdown of glycogen.
6. Which cells release insulin when glucose levels elevate in the body?
a) zeta cells
b) alpha cells
c) gamma cells
d) beta cells
View Answer
Explanation: The beta cells in pancreas secrete insulin when the blood glucose levels elevate while the alpha cells in the pancreas secrete glucagon when the blood glucose levels drop. Insulin acts as an extracellular messenger molecule.
7. Which of the following synthesis is decreased (or stopped) when the blood glucose levels are high?
a) gluconeogenesis
b) triglyceride
c) glycogen
d) glucagon
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Explanation: When the blood sugar levels are high, the uptake of glucose and synthesis of glycogen and triglycerides increases while the gluconeogenesis is decreased. Gluconeogenesis is the process of synthesis of glucoses from non-sugar substrates such as pyruvate.
8. Diabetes Mellitus is caused by defects in insulin signaling.
a) True
b) False
View Answer
Explanation: Diabetes Mellitus is a common human disorder that is caused by defects in insulin signaling. The type I diabetes accounts for 5-10% cases and the type II accounts for remaining 90-95%.
9. Diabetes Mellitus type II is caused due __________________________
a) inability to produce insulin
b) insulin resistance
c) low glucose levels
d) low lactose levels
View Answer
Explanation: Diabetes Mellitus type II is caused due to insulin resistance that results from the elevated levels of glucose in the blood and subsequent increase in insulin (overstimulation). As a result of this, the target cells, those having insulin receptors stop responding to the presence of the hormone.
10. How many subunits does the Ras protein contain?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: The Ras proteins belong to the superfamily of G-proteins and contain one small subunit, also called monomeric G-protein. Ras is a GTPase anchored by a lipid group on the inner surface of a plasma membrane.
11. The Etr1 gene in plants encodes for ___________________
a) ethylene gas
b) ethylene gas receptor
c) hydrogen sulfide
d) hydrogen sulfide receptor
View Answer
Explanation: The Etr1 gene in plants encodes for a receptor of the ethylene gas (C2H2). Ethylene is a plant hormone that regulates a variety of developmental processes such as seed germination and fruit ripening.
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