All Free Biochemistry MCQs with Answers

• A. Albumin
• B. Firbinogen
• C. Lecithin
• D. Globulin

Explanation: Fibrinogen is present in plasma but removed during clot formation, so it is absent from serum.

• A. Phenyl lactate
• B. 3- Hydroxy phenyl pyruvate
• C. 5- Hydroxy indole acetate
• D. Phenyl acetate

Explanation: Argentaffinoma, commonly associated with a serotonin-secreting carcinoid tumour, produces excess serotonin that is metabolised to…

• A. Boiling test
• B. Hay's test
• C. Barfoed test
• D. Ehrlich's test

Explanation: The boiling test detects urinary protein because proteins coagulate on heating, producing turbidity or a precipitate.

• A. All of the above
• B. Ornithine
• C. Arginine
• D. Lysine
• E. Cystine

Explanation: Cystinosis causes a proximal tubular reabsorption defect with generalised aminoaciduria, including cystine, ornithine, arginine and…

• A. Histidine
• B. Cystine
• C. Tyrosine
• D. Alanine

Explanation: Albinism commonly results from deficient tyrosinase activity, which disrupts the conversion of tyrosine into melanin.

• A. Leucine
• B. Isoleucine
• C. Valine
• D. All of the above

Explanation: Maple syrup urine disease results from deficiency of the branched-chain alpha-ketoacid dehydrogenase complex, causing leucine, isoleucine…

• A. Low platelet count
• B. Increased prothrombin time
• C. Decreased prothrombin time
• D. None of the above

Explanation: Vitamin K is needed to produce functional clotting factors, so deficiency prolongs the prothrombin time.

• A. Glyceraldehyde 3 phosphate dehydrogenase
• B. Lactate dehydrogenase
• C. Glucose 6-Phosphate dehydrogenase
• D. Beta hydroxy acyl CoA dehydrogenaseOrder DNA Kits

Explanation: Glucose 6-phosphate dehydrogenase uses NADP+ and produces NADPH in the pentose phosphate pathway.

• A. Pyruvate dehydrogenase
• B. Both A & B
• C. Succinate dehydrogenase
• D. Enolase
• E. Alpha ketoglutarate dehydrogenase

Explanation: Both pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase are multienzyme complexes containing several catalytic components and…

• A. Pyruvate carboxylase
• B. Lactate dehydrogenase
• C. Succinate thiokinase
• D. Phosphohexose isomerase

Explanation: Biotin is the covalently bound cofactor for carboxylases and carries activated carbon dioxide during carboxylation.

• A. Apoenzymes
• B. Coenzymes
• C. Proenzymes
• D. Holoenzymes

Explanation: Inactive enzyme precursors are called proenzymes or zymogens and become active after specific proteolytic cleavage.

• A. Zymogen
• B. Coenzyme
• C. Antienzyme
• D. Isozyme

Explanation: Lactate dehydrogenase exists as five molecular forms made from different combinations of H and M subunits, so it is an isozyme.

• A. Holoenzyme
• B. Coenzyme
• C. Apoenzyme
• D. Constitutive enzyme

Explanation: A holoenzyme is the complete, active enzyme formed when the apoenzyme combines with its required cofactor or coenzyme.

• A. Adenylate cyclase
• B. Polymerase
• C. ATP synthase
• D. Tyrosine kinase

Explanation: Adenylate cyclase is a membrane-bound enzyme that converts ATP into cyclic AMP, an important second messenger.

• A. Glutamine synthetase
• B. Cholinesterase
• C. Fumarase
• D. Amylase

Explanation: Fumarase is a lyase because it catalyses the reversible addition or removal of groups without hydrolysis or oxidation, converting fumarate…

• A. Pro enzyme
• B. HoloenzymeOrder DNA Kits
• C. Co-enzyme
• D. Iso enzyme

Explanation: Isoenzymes are different molecular forms of an enzyme that catalyse the same reaction but differ in properties such as structure…

• A. Lowering the activation energy
• B. Increasing the substrate concentration
• C. Decreasing the surface tension
• D. Increasing the activation energy

Explanation: Enzymes accelerate reactions by lowering the activation energy needed to reach the transition state.

• A. Transketolase
• B. Carboxylase
• C. Oxidase
• D. Dehydrogenase

Explanation: Biotin carries carbon dioxide in carboxylation reactions, so enzymes such as pyruvate carboxylase and acetyl-CoA carboxylase lose activity…

• A. Decrease of km and increase of Vmax
• B. increase of km and increase of Vmax
• C. Decrease of km and decrease of Vmax
• D. Increase of km and Unchanged of Vmax

Explanation: A competitive inhibitor competes at the active site, so a higher substrate concentration is needed to reach half-maximal velocity…

• A. Ferro protoporphyrin
• B. FAD
• C. NADP+
• D. FMN

Explanation: Dehydrogenases commonly use NAD+, NADP+, FAD, or FMN to transfer hydrogen or electrons.