Cell Biology Questions and Answers – Enzymes as Biological Catalysts


This set of Tricky Cell Biology Questions and Answers focuses on “Enzymes as Biological Catalysts”.

1. Why are enzymes required?
a) Enzymes help to yield more product
b) Enzymes increase the activation energy of the reaction
c) Enzymes decrease the activation energy of the reaction
d) Enzymes maintain the equilibrium in the reaction
View Answer

Answer: c
Explanation: Chemical reactions need certain covalent bond breakage within the reactants. For this, the reactants must contain sufficient kinetic energy called the activation energy. Enzymes act as catalysts that speed up the reaction by lowering the activation energy required for breaking the covalent bonds.

2. Competitive enzyme inhibitors are ________
a) Reversible inhibitors
b) Irreversible inhibitors
c) Permanent inhibitors
d) None of the mentioned
View Answer

Answer: a
Explanation: Irreversible inhibitors are those that bind very tightly to an enzyme, often by forming a covalent bond to one of its amino acid residues. Reversible inhibitors bind loosely to an enzyme and thus are readily displaced. Competitive inhibitors are reversible inhibitors of enzyme that compete with a substrate for access to the active site of the enzyme.

3. Which of the following is a non-competitive inhibitor against protease produced by HIV?
a) Tipranavir
b) Acetylcholinesterase
c) Ritonavir
d) Phenicols
View Answer

Answer: a
Explanation: In noncompetitive inhibition, the substrate and inhibitor do not compete for the active site of the enzyme and the inhibitor generally act at other site to bind to the enzyme. The level of inhibition depends on concentration of the inhibitor. Tipranavir is non-competitive inhibitor of the protease produced by HIV when HIV infects a white blood cell. Ritonavir is a competitive inhibitor of the protease and resembles the its peptide substate.

4. Allosteric enzymes are which _______
a) Have single subunit
b) Have multiple subunits
c) Follows Michaelis-Menten kinetics
d) Do not affect the binding affinity
View Answer

Answer: b
Explanation: Allosteric enzymes are enzymes that change conformation upon binding of an effector and affects the binding affinity at a different binding site. Allosteric enzymes are the exception to Michaelis-Menten kinetics and usually has multiple coupled subunits or domains.

5. Feedback inhibition occurs due to _______
a) Excess of the reactants in the reaction
b) Presence of competitive inhibitor
c) Increase in product to a certain level
d) Presence of irreversible inhibitor
View Answer

Answer: c
Explanation: Feedback inhibition refers to the inhibition of enzyme activity when a certain end product is increased beyond a certain level. Due to accumulation of the product, the enzyme does form the enzyme-substrate complex in order to form the product, which is already in excess.

6. Enzymes that transfer the phosphate group from one protein to another is called _____
a) Phosphatase
b) Phosphate transferase
c) Kinase
d) Phosphorylase
View Answer

Answer: c
Explanation: Kinase is the enzyme that transfers phosphate group from one protein to another. Phosphorylase catalyzes addition of phosphate group from an inorganic phosphate to an acceptor. Phosphatase enzyme cleaves a phosphate in presence of water.

7. The enzyme that catalyzes the transfer of a proton from a reactant to NAD+ is known as ______
a) Hydrolase
b) Proton carrier
c) Dehydrogenase
d) None of the mentioned
View Answer

Answer: c
Explanation: Dehydrogenase is the enzyme that catalyzes the removal of a proton tor hydrogen from a reactant to NAD+. NADH is the reduced form of NAD+, which is a cofactor in the electron transport chain.

8. The functions of ATP are ___________
a) ATP acts as the main source of energy in cells
b) Plays a role in transporting solutes and proteins across cell membranes
c) Contribute to the building blocks of DNA
d) All of the mentioned
View Answer

Answer: d
Explanation: Adenosine triphosphate or ATP is the main source of energy in cells. It releases energy by breaking into Adenosine diphosphate (ADP) and inorganic phosphate. It plays a role in solute transport across cell membranes through ATPase channels. It is the precursor of Adenine, which helps in the formation of DNA.

9. In anaerobic respiration, pyruvic acid is converted to _______
a) Lactate
b) Acetyl CoA
c) PEP
d) Acetate
View Answer

Answer: a
Explanation: In aerobic respiration, the pyruvate is converted to two-carbon compound acetyl CoA which enters the Kreb’s cycle to release carbon dioxide and energy. In anaerobic respiration, due to absence of oxygen, the pyruvate is converted to lactate. In yeast fermentation, pyruvate is converted to alcohol and carbon dioxide.

10. The cofactor in Haber’s process is __________
a) Molybdenum
b) Iron
c) Copper
d) Magnesium
View Answer

Answer: a
Explanation: The process of formation of ammonia from hydrogen and nitrogen is known as the Haber’s process. The enzyme that catalyzes the Haber’s reaction needs Molybdenum (Mo) as a cofactor.

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