All Free Biochemistry MCQs with Answers

• A. Cytochrome oxidase
• B. PeroxidaseOrder DNA Kits
• C. Hydrolase
• D. Dehydrogenase

Explanation: Peroxidase uses hydrogen peroxide to oxidize chromogenic substances such as benzidine, producing a characteristic positive colour…

• A. Carbomoyl Phosphate synthetase
• B. Malonyl CoA carboxylase
• C. Fatty acid synthetase
• D. Adenosine phospho ribosyl transferase

Explanation: Fatty acid synthetase is a multifunctional multienzyme complex containing several catalytic activities in one assembly.

• A. Follow Michaelis-Menton Kinetics
• B. They are multienzyme complex
• C. Presence of Modulator site
• D. Give sigmoid shaped curve

Explanation: Allosteric enzymes generally show cooperative, sigmoid kinetics rather than the hyperbolic Michaelis-Menten curve.

• A. Tocopherol
• B. Catalase
• C. Superoxide dismutase
• D. Urate

Explanation: Catalase is a preventive antioxidant because it removes hydrogen peroxide before it can generate more damaging reactive oxygen species.

• A. 5
• B. 3
• C. 11
• D. 2

Explanation: Lactate dehydrogenase has five isoenzymes, LDH-1 through LDH-5, formed from different combinations of H and M subunits.

• A. Cyclic AMP
• B. Adenosine tri phosphate
• C. Citrate
• D. Fructose 2,6 bis phosphate

Explanation: Fructose 2,6-bisphosphate is the strongest activator of phosphofructokinase-1 and promotes glycolysis.

• A. Phosphatase
• B. ATPase
• C. Dismutase
• D. Aldolase

Explanation: Magnesium commonly stabilises ATP and is required for the activity of many ATPases and phosphate-transfer enzymes.

• A. Apoenzyme
• B. Coenzyme
• C. Cofactor
• D. Holoenzyme

Explanation: An inorganic ion that is tightly associated with an enzyme and required for its activity is termed a cofactor.

• A. Activate the substrate
• B. Increase the active sites of apoenzyme
• C. Enhance the specificity of apoenzyme
• D. Accept one of the cleavage products

Explanation: Coenzymes act as carriers of chemical groups or electrons during enzyme reactions, often accepting a product or reaction fragment and…

• A. Glucose 1,6 diphosphatase
• B. Glucose 6 phosphatase
• C. Hexokinase
• D. Glucose 6 phosphate dehydrogenase

Explanation: Glucose-6-phosphate dehydrogenase deficiency is the most common clinically significant inherited enzyme deficiency worldwide.

• A. Cytochromes
• B. Catalase
• C. Super oxide dismutase
• D. Cytochrome P 450

Explanation: Catalase decomposes hydrogen peroxide into water and molecular oxygen: 2H₂O₂ → 2H₂O + O₂.

• A. Oxidases
• B. Peptidases
• C. Transferases
• D. LIpases

Explanation: Transferases move a functional group, such as an amino, phosphate, or methyl group, from one molecule to another.

• A. All of the above
• B. Action of coenzymes
• C. Nature of the enzymes
• D. Action on substrate

Explanation: Enzymes are classified mainly by the type of reaction they catalyse, or their action on the substrate, such as oxidation, transfer…

• A. A catalyst
• B. A base
• C. A solvent
• D. Thermoplastic

Explanation: A catalyst increases the rate of a chemical reaction without being consumed or permanently changed.

• A. Dissociation constant
• B. The normal physiological substrate concentration
• C. Substrate concentration at half maximal velocity
• D. Numerically identical for all isozymes that catalyses a given reaction

Explanation: Km is the substrate concentration at which an enzyme reaches half of its maximum velocity, Vmax.

• A. Rate of enzymatic reaction is independent of substrate concentration
• B. Rate of non enzymatic reaction is proportional to substrate concentration
• C. Km is the enzyme substrate complex association constant
• D. Enzyme- substrate complex formation is essential in enzymatic reactionOrder DNA Kits

Explanation: Michaelis-Menten kinetics assumes that the enzyme first binds the substrate to form an enzyme-substrate complex, which then produces…

• A. Transferase
• B. Reductase
• C. Oxidoreductase
• D. Oxidase

Explanation: Hexokinase transfers a phosphate group from ATP to glucose, forming glucose-6-phosphate.

• A. Apoenzyme
• B. Holoenzyme
• C. Protoenzyme
• D. Proenzyme

Explanation: The protein portion alone is the apoenzyme, whereas the active enzyme formed by combining an apoenzyme with its coenzyme or other cofactor…

• A. Structural proteins
• B. Substrate protiens
• C. Pigment
• D. Polymer

Explanation: In cytochrome P450, P stands for pigment because these heme-containing proteins show a characteristic absorption peak near 450 nm when…

• A. Oxidase
• B. Hydrolase
• C. Peroxidase
• D. Dehydrogenase

Explanation: Respiratory burst begins with activation of NADPH oxidase in phagocytes, producing superoxide radicals for microbial killing.