This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Gene Regulation Ensures a Physiological Response”.
1. Regulation of enzyme activity is accomplished in ___________ steps.
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: Regulation of enzyme activity plays a key role in governing the cell behavior. Thus its regulation comes in two specific steps. The first step is accomplished in part at the level of gene expression, which determines the amount of any protein synthesized by the cell. A further level of control is then obtained by regulation of protein function, which allows the cell to regulate not only the amount but also the activities of its proteins.
2. Binding of small molecules to enzymes leads to feedback inhibition.
a) True
b) False
View Answer
Explanation: Conformational changes in the enzymes result from the binding of small molecules, such as, amino acids or nucleotides that regulate enzyme activity. This type of regulation commonly is responsible for controlling metabolic pathways by the process of feedback inhibition.
3. The regulatory molecules bind to the catalytic site of an enzyme to regulate its activity.
a) True
b) False
View Answer
Explanation: Feedback inhibition is an example of allosteric regulation, in which a regulatory molecule binds to a site on an enzyme that is distinct from the catalytic site. The binding of such regulatory molecules alters the conformation of the protein, thereby changing the shape of the catalytic site and affecting catalytic activity.
4. Which of the following is incorrect about the inactive state of the Ras protein?
a) GDP bound form
b) Cell proliferation activation
c) Mutation leads to cancer
d) Changes configuration when bound to regulatory molecules
View Answer
Explanation: Ras protein when bound to GDP, that is, in its inactive form, cannot activate cell proliferation. It can only activate cell proliferation when it is in the active GTP bound state.
5. The regulatory proteins bind to the enzymes with covalent linkages.
a) True
b) False
View Answer
Explanation: The regulatory proteins bind to the enzymes with non-covalent linkages. Since no covalent bonds are formed, the binding of these regulatory molecules to the protein is readily reversible, allowing the cell to respond rapidly to environmental changes.
6. The activity of which of the following proteins is not regulated by covalent modifications?
a) Digestive enzymes
b) Apoptosis
c) Cell signaling
d) Blood clotting
View Answer
Explanation: The activity of many proteins is regulated by covalent modifications. One example of this type of regulation is the activation of some enzymes by proteolytic cleavage of inactive precursors. Digestive enzymes and proteins involved in blood clotting and apoptosis are regulated in this mechanism.
7. Protein kinases transfer phosphate groups to the side chains of which of the following?
a) Serine
b) Valine
c) Glutamate
d) Lysine
View Answer
Explanation: Protein phosphorylation is catalyzed by protein kinases, most of which transfer phosphate groups from ATP to the hydroxyl groups of the side chains of serine, threonine or tyrosine residues. The protein kinases are one of the largest protein families in eukaryotes, accounting for approximately 2% of eukaryotic genes.
8. Like kinases all phosphatases are also species specific in nature.
a) True
b) False
View Answer
Explanation: Like protein kinases, most protein phosphatases are specific either for serine and threonine or for tyrosine residues. But some protein phosphatases can recognize all the three phosphoamino acids.
9. Which of the following is false about amino acid modification and activity?
a) Acetylation of lysine residue
b) Methylation of lysine and arginine residue
c) Glycosylation of serine and threonine residue
d) Nitrosylation of arginine residue
View Answer
Explanation: Nitrosylation is the addition of NO groups to the side chains of amino acids. Nitrosylation generally occurs to the cystine residues of protein polypeptide chains and not arginine.
10. The cAMP-dependent protein kinase has how many subunits?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: The cAMP-dependent protein kinase is composed of two regulatory subunits and two catalytic subunits. In this state the enzyme is inactive. The enzyme is activated by cAMP, which binds to the regulatory subunits and induces a conformational change leading to dissociation of the complex; the free catalytic subunits are then enzymatically active protein kinase.
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