Biochemistry MCQs
🔬 Biochemistry MCQs – Part 1 (Q1–Q25)
Q1. The basic structural unit of proteins is:
A) Monosaccharide
B) Amino acid
C) Nucleotide
D) Fatty acid
✅ Answer: B) Amino acid
Explanation: Proteins are polymers of amino acids linked by peptide bonds.
Q2. The bond joining amino acids in proteins is called:
A) Hydrogen bond
B) Peptide bond
C) Disulfide bond
D) Glycosidic bond
✅ Answer: B) Peptide bond
Explanation: Peptide bond is a covalent bond formed between carboxyl group and amino group.
Q3. Which amino acid contains sulfur?
A) Glycine
B) Methionine
C) Alanine
D) Serine
✅ Answer: B) Methionine
Explanation: Sulfur-containing amino acids are methionine and cysteine.
Q4. The secondary structure of proteins is stabilized by:
A) Ionic bonds
B) Hydrogen bonds
C) Peptide bonds
D) Hydrophobic interactions
✅ Answer: B) Hydrogen bonds
Explanation: α-helices and β-sheets are stabilized by H-bonds between peptide groups.
Q5. The three-dimensional structure of a protein is its:
A) Primary structure
B) Secondary structure
C) Tertiary structure
D) Quaternary structure
✅ Answer: C) Tertiary structure
Explanation: Tertiary structure = overall 3D folding stabilized by disulfide bonds, ionic interactions, H-bonds.
Q6. Hemoglobin is an example of:
A) Primary protein
B) Tertiary protein
C) Quaternary protein
D) Secondary protein
✅ Answer: C) Quaternary protein
Explanation: Hemoglobin has 4 polypeptide chains = quaternary structure.
Q7. Enzymes are:
A) Lipids
B) Proteins
C) Carbohydrates
D) Nucleic acids
✅ Answer: B) Proteins
Explanation: Most enzymes are proteins, except some catalytic RNAs (ribozymes).
Q8. The enzyme that digests starch is:
A) Lipase
B) Protease
C) Amylase
D) Pepsin
✅ Answer: C) Amylase
Explanation: Amylase hydrolyzes starch → maltose.
Q9. The enzyme activity is measured in terms of:
A) moles
B) Units (U)
C) ATP concentration
D) Enzyme concentration
✅ Answer: B) Units (U)
Explanation: One enzyme unit = amount converting 1 μmol substrate/min under standard conditions.
Q10. The coenzyme required for transamination reactions is:
A) NAD⁺
B) FAD
C) Pyridoxal phosphate (PLP)
D) Coenzyme A
✅ Answer: C) PLP
Explanation: PLP (vitamin B₆ derivative) is essential in amino acid metabolism.
Q11. The energy currency of the cell is:
A) GTP
B) ATP
C) NADH
D) FADH₂
✅ Answer: B) ATP
Explanation: ATP is the universal energy carrier in cells.
Q12. The first law of thermodynamics states:
A) Entropy increases in all processes
B) Energy can neither be created nor destroyed
C) All reactions are spontaneous
D) Energy is always lost as heat
✅ Answer: B)
Explanation: Energy is transformed, not created/destroyed.
Q13. Enzymes increase the rate of reactions by:
A) Increasing activation energy
B) Lowering activation energy
C) Changing free energy of reaction
D) Changing equilibrium
✅ Answer: B)
Explanation: Enzymes lower activation energy without altering equilibrium.
Q14. Km (Michaelis constant) represents:
A) Maximum velocity of enzyme
B) Substrate concentration at half Vmax
C) Enzyme concentration
D) Inhibitor concentration
✅ Answer: B)
Explanation: Km = [S] at ½ Vmax, indicates enzyme affinity (low Km = high affinity).
Q15. Which enzyme is inhibited by cyanide?
A) Hexokinase
B) Cytochrome oxidase
C) Lactate dehydrogenase
D) Amylase
✅ Answer: B) Cytochrome oxidase
Explanation: Cyanide inhibits Complex IV of ETC, blocking respiration.
Q16. The process of glucose breakdown to pyruvate is called:
A) Gluconeogenesis
B) Glycolysis
C) Glycogenesis
D) Pentose phosphate pathway
✅ Answer: B) Glycolysis
Explanation: Glycolysis = glucose → pyruvate, producing ATP and NADH.
Q17. The enzyme hexokinase catalyzes the conversion of:
A) Glucose → Glucose-6-phosphate
B) Glucose → Fructose
C) Glucose → Pyruvate
D) Glucose → Lactate
✅ Answer: A)
Explanation: Hexokinase phosphorylates glucose in first step of glycolysis.
Q18. The net gain of ATP in glycolysis per glucose molecule is:
A) 2 ATP
B) 4 ATP
C) 6 ATP
D) 8 ATP
✅ Answer: A) 2 ATP
Explanation: Glycolysis: 4 ATP produced, 2 consumed → net 2 ATP (plus 2 NADH).
Q19. In anaerobic glycolysis, pyruvate is converted into:
A) Acetyl-CoA
B) Lactate
C) Ethanol
D) CO₂
✅ Answer: B) Lactate
Explanation: In humans, anaerobic glycolysis forms lactate (via lactate dehydrogenase).
Q20. The link between glycolysis and TCA cycle is:
A) Lactate
B) Acetyl-CoA
C) Oxaloacetate
D) Citrate
✅ Answer: B) Acetyl-CoA
Explanation: Pyruvate → Acetyl-CoA (via pyruvate dehydrogenase) → enters TCA cycle.
Q21. The first step of the TCA cycle is formation of:
A) Citrate
B) Oxaloacetate
C) α-Ketoglutarate
D) Fumarate
✅ Answer: A) Citrate
Explanation: Acetyl-CoA + oxaloacetate → citrate (via citrate synthase).
Q22. How many ATP are produced by complete oxidation of 1 glucose molecule?
A) 28
B) 30–32
C) 36
D) 40
✅ Answer: B) 30–32 ATP
Explanation: Aerobic respiration yields ~30–32 ATP/glucose.
Q23. Which complex of the ETC pumps protons and transfers electrons from NADH?
A) Complex I
B) Complex II
C) Complex III
D) Complex IV
✅ Answer: A) Complex I
Explanation: NADH dehydrogenase (Complex I) oxidizes NADH and pumps protons.
Q24. Which enzyme is known as the “universal energy transducer”?
A) ATP synthase
B) Hexokinase
C) Lactate dehydrogenase
D) Pyruvate kinase
✅ Answer: A) ATP synthase
Explanation: ATP synthase converts proton motive force → ATP.
Q25. The pentose phosphate pathway primarily produces:
A) NADH and ATP
B) NADPH and ribose-5-phosphate
C) Pyruvate and lactate
D) Acetyl-CoA and citrate
✅ Answer: B) NADPH and ribose-5-phosphate
Explanation: PPP generates NADPH (for biosynthesis) + ribose-5-P (for nucleotides).
🔬 Biochemistry MCQs – Part 2 (Q26–Q50)
Q26. The main storage form of glucose in animals is:
A) Starch
B) Glycogen
C) Cellulose
D) Lactose
✅ Answer: B) Glycogen
Explanation: Animals store glucose as glycogen (branched polysaccharide). Plants store starch.
Q27. The enzyme glycogen phosphorylase is involved in:
A) Glycolysis
B) Glycogenesis
C) Glycogenolysis
D) Gluconeogenesis
✅ Answer: C) Glycogenolysis
Explanation: Glycogen phosphorylase releases glucose-1-phosphate from glycogen.
Q28. The key regulatory enzyme of glycolysis is:
A) Hexokinase
B) Phosphofructokinase-1 (PFK-1)
C) Pyruvate kinase
D) Aldolase
✅ Answer: B) PFK-1
Explanation: PFK-1 is the rate-limiting enzyme of glycolysis.
Q29. Which of the following is NOT a gluconeogenic substrate?
A) Lactate
B) Glycerol
C) Acetyl-CoA
D) Alanine
✅ Answer: C) Acetyl-CoA
Explanation: Acetyl-CoA cannot form glucose because pyruvate → acetyl-CoA is irreversible.
Q30. The Cori cycle links:
A) Liver and kidney
B) Muscle and liver
C) Brain and muscle
D) Adipose tissue and liver
✅ Answer: B) Muscle and liver
Explanation: Lactate produced in muscle → transported to liver → converted back to glucose.
Q31. Which vitamin is required for carboxylation reactions?
A) Vitamin B1
B) Vitamin B6
C) Biotin (B7)
D) Folate
✅ Answer: C) Biotin (B7)
Explanation: Biotin = coenzyme for carboxylases (adds CO₂).
Q32. The main site of gluconeogenesis is:
A) Muscle
B) Liver
C) Kidney
D) Pancreas
✅ Answer: B) Liver
Explanation: Gluconeogenesis occurs mainly in the liver (and kidney during starvation).
Q33. The key regulatory enzyme of gluconeogenesis is:
A) Hexokinase
B) Pyruvate carboxylase
C) Phosphoenolpyruvate carboxykinase (PEPCK)
D) Fructose-1,6-bisphosphatase
✅ Answer: D) Fructose-1,6-bisphosphatase
Explanation: It bypasses PFK-1 step → key regulatory enzyme of gluconeogenesis.
Q34. The lipids that form the main structural component of membranes are:
A) Steroids
B) Triglycerides
C) Phospholipids
D) Fatty acids
✅ Answer: C) Phospholipids
Explanation: Phospholipids form bilayer membranes with hydrophilic heads and hydrophobic tails.
Q35. Essential fatty acids include:
A) Oleic acid
B) Stearic acid
C) Linoleic acid
D) Palmitic acid
✅ Answer: C) Linoleic acid
Explanation: Linoleic and linolenic acids are essential (cannot be synthesized by humans).
Q36. β-oxidation of fatty acids occurs in the:
A) Cytosol
B) Mitochondria
C) Nucleus
D) Endoplasmic reticulum
✅ Answer: B) Mitochondria
Explanation: Fatty acids are oxidized in mitochondria to acetyl-CoA.
Q37. The end product of odd-chain fatty acid oxidation is:
A) Acetyl-CoA only
B) Propionyl-CoA
C) Succinyl-CoA
D) Malonyl-CoA
✅ Answer: B) Propionyl-CoA
Explanation: Odd-chain fatty acids yield propionyl-CoA, converted to succinyl-CoA.
Q38. Ketone bodies are produced during:
A) High carbohydrate diet
B) Fasting and starvation
C) Protein-rich diet
D) Anaerobic respiration
✅ Answer: B) Fasting and starvation
Explanation: Liver produces ketone bodies (acetoacetate, β-hydroxybutyrate, acetone) during starvation.
Q39. The main nitrogenous waste in humans is:
A) Ammonia
B) Urea
C) Uric acid
D) Creatinine
✅ Answer: B) Urea
Explanation: Humans are ureotelic, excreting urea via urea cycle.
Q40. The rate-limiting enzyme of the urea cycle is:
A) Arginase
B) Carbamoyl phosphate synthetase I
C) Ornithine transcarbamylase
D) Argininosuccinate lyase
✅ Answer: B) CPS-I
Explanation: CPS-I is the rate-limiting enzyme of urea cycle in mitochondria.
Q41. The major site of protein digestion in humans is:
A) Mouth
B) Stomach
C) Small intestine
D) Large intestine
✅ Answer: C) Small intestine
Explanation: Majority of protein digestion occurs in duodenum and jejunum by pancreatic enzymes.
Q42. The enzyme that digests proteins in the stomach is:
A) Pepsin
B) Trypsin
C) Chymotrypsin
D) Carboxypeptidase
✅ Answer: A) Pepsin
Explanation: Pepsin (from pepsinogen) breaks proteins into peptides.
Q43. Which vitamin is essential for collagen synthesis?
A) Vitamin A
B) Vitamin C
C) Vitamin D
D) Vitamin E
✅ Answer: B) Vitamin C
Explanation: Vitamin C = cofactor for prolyl hydroxylase in collagen synthesis.
Q44. The major storage form of lipids is:
A) Phospholipids
B) Steroids
C) Triglycerides
D) Waxes
✅ Answer: C) Triglycerides
Explanation: Stored in adipose tissue for energy reserves.
Q45. Lipoproteins that transport cholesterol from tissues to liver are:
A) Chylomicrons
B) VLDL
C) LDL
D) HDL
✅ Answer: D) HDL
Explanation: HDL = good cholesterol, carries cholesterol back to liver.
Q46. Which amino acid is the precursor of serotonin?
A) Tyrosine
B) Tryptophan
C) Glycine
D) Phenylalanine
✅ Answer: B) Tryptophan
Explanation: Tryptophan → serotonin (5-HT) via hydroxylation and decarboxylation.
Q47. Which amino acid is the precursor of dopamine?
A) Tyrosine
B) Tryptophan
C) Glycine
D) Histidine
✅ Answer: A) Tyrosine
Explanation: Tyrosine → DOPA → dopamine → norepinephrine → epinephrine.
Q48. The coenzyme required for transamination is:
A) Biotin
B) Pyridoxal phosphate (Vitamin B6)
C) Thiamine pyrophosphate (Vitamin B1)
D) Folic acid
✅ Answer: B) Pyridoxal phosphate
Explanation: PLP is coenzyme for aminotransferases.
Q49. The enzyme that removes ammonia from glutamate is:
A) Glutamate synthase
B) Glutamate dehydrogenase
C) Glutamine synthetase
D) Alanine transaminase
✅ Answer: B) Glutamate dehydrogenase
Explanation: Converts glutamate → α-ketoglutarate + NH₃.
Q50. The main role of folic acid in metabolism is:
A) Transfer of methyl groups
B) Fatty acid synthesis
C) Protein synthesis
D) Glycogen synthesis
✅ Answer: A) Transfer of methyl groups
Explanation: Folic acid derivatives carry one-carbon units for nucleotide synthesis.
🔬 Biochemistry MCQs – Part 3 (Q51–Q75)
Q51. The genetic material of most viruses is:
A) Double-stranded DNA
B) RNA or DNA
C) Only RNA
D) Protein
✅ Answer: B) RNA or DNA
Explanation: Viruses may contain DNA (e.g., adenovirus) or RNA (e.g., influenza, HIV) as genetic material.
Q52. Nucleotides are composed of:
A) Sugar + base
B) Sugar + phosphate
C) Base + phosphate
D) Sugar + base + phosphate
✅ Answer: D)
Explanation: Nucleotide = pentose sugar + nitrogenous base + phosphate group.
Q53. The sugar present in RNA is:
A) Deoxyribose
B) Ribose
C) Glucose
D) Fructose
✅ Answer: B) Ribose
Explanation: RNA contains ribose, while DNA contains deoxyribose.
Q54. DNA is stabilized by:
A) Covalent bonds only
B) Hydrogen bonds between bases
C) Peptide bonds
D) Ionic bonds
✅ Answer: B)
Explanation: DNA double helix stabilized by hydrogen bonds (A–T = 2, G–C = 3).
Q55. Chargaff’s rule states that in DNA:
A) A = T, G = C
B) A = G, T = C
C) A = C, G = T
D) A + G = T + C
✅ Answer: A) and D) both
Explanation: A = T, G = C, and total purines = total pyrimidines.
Q56. The enzyme that synthesizes DNA is:
A) DNA polymerase
B) RNA polymerase
C) Ligase
D) Primase
✅ Answer: A) DNA polymerase
Explanation: DNA polymerase catalyzes 5′→3′ DNA synthesis.
Q57. The Okazaki fragments are found on the:
A) Leading strand
B) Lagging strand
C) Both strands
D) RNA
✅ Answer: B) Lagging strand
Explanation: Lagging strand synthesized discontinuously as Okazaki fragments.
Q58. The enzyme that joins Okazaki fragments is:
A) DNA polymerase
B) DNA ligase
C) Helicase
D) Topoisomerase
✅ Answer: B) DNA ligase
Explanation: DNA ligase seals phosphodiester bonds between fragments.
Q59. Transcription is the process of:
A) DNA → DNA
B) DNA → RNA
C) RNA → Protein
D) Protein → DNA
✅ Answer: B) DNA → RNA
Explanation: Transcription forms mRNA from DNA template.
Q60. The enzyme responsible for transcription is:
A) DNA polymerase
B) RNA polymerase
C) Reverse transcriptase
D) Helicase
✅ Answer: B) RNA polymerase
Explanation: RNA polymerase synthesizes RNA from DNA template.
Q61. Translation is the process of:
A) DNA → RNA
B) RNA → Protein
C) Protein → DNA
D) RNA → RNA
✅ Answer: B) RNA → Protein
Explanation: Translation = protein synthesis on ribosomes.
Q62. The codon AUG codes for:
A) Methionine (start codon)
B) Tryptophan
C) Glycine
D) Stop
✅ Answer: A) Methionine
Explanation: AUG = start codon (Met).
Q63. The stop codons are:
A) UAA, UAG, UGA
B) AUG, UAG, UAA
C) UAA, AUG, UGA
D) UAG, AUG, GUA
✅ Answer: A) UAA, UAG, UGA
Explanation: These codons signal termination of translation.
Q64. The wobble hypothesis explains:
A) DNA replication errors
B) Flexibility in base pairing of tRNA anticodon
C) Protein misfolding
D) RNA splicing
✅ Answer: B)
Explanation: Wobble hypothesis: third codon position allows flexible pairing.
Q65. The main high-energy compound in muscle contraction is:
A) ATP
B) GTP
C) Creatine phosphate
D) FADH₂
✅ Answer: C) Creatine phosphate
Explanation: Creatine phosphate regenerates ATP during muscle contraction.
Q66. Hemoglobin has maximum affinity for:
A) O₂
B) CO₂
C) CO (carbon monoxide)
D) NO
✅ Answer: C) CO
Explanation: Hemoglobin binds CO ~200x stronger than O₂ → toxic effect.
Q67. Sickle-cell anemia results from substitution of:
A) Valine for glutamic acid in β-chain
B) Glutamic acid for valine in β-chain
C) Lysine for glutamic acid
D) Alanine for glycine
✅ Answer: A)
Explanation: Mutation: β-globin Glu → Val at position 6, causing sickling.
Q68. The oxygen-binding curve of myoglobin is:
A) Sigmoidal
B) Hyperbolic
C) Linear
D) Exponential
✅ Answer: B) Hyperbolic
Explanation: Myoglobin binds O₂ independently (no cooperativity). Hemoglobin = sigmoidal.
Q69. The enzyme inhibited by aspirin is:
A) Amylase
B) Cyclooxygenase (COX)
C) Lipase
D) Protease
✅ Answer: B) COX
Explanation: Aspirin irreversibly inhibits COX → ↓ prostaglandin, thromboxane synthesis.
Q70. The enzyme reverse transcriptase is found in:
A) DNA viruses
B) RNA viruses (retroviruses)
C) Bacteria
D) Ribosomes
✅ Answer: B) Retroviruses
Explanation: Reverse transcriptase copies RNA → DNA (e.g., HIV).
Q71. The major plasma protein responsible for maintaining osmotic pressure is:
A) Globulin
B) Albumin
C) Fibrinogen
D) Hemoglobin
✅ Answer: B) Albumin
Explanation: Albumin maintains oncotic pressure and transports molecules.
Q72. Hyperuricemia (↑ uric acid) leads to:
A) Rickets
B) Gout
C) Anemia
D) Scurvy
✅ Answer: B) Gout
Explanation: Excess uric acid crystallizes in joints → gout arthritis.
Q73. Phenylketonuria (PKU) is due to deficiency of:
A) Tyrosinase
B) Phenylalanine hydroxylase
C) Homogentisate oxidase
D) Glucose-6-phosphatase
✅ Answer: B) Phenylalanine hydroxylase
Explanation: PKU → defective phenylalanine → tyrosine metabolism.
Q74. Alkaptonuria is due to deficiency of:
A) Tyrosinase
B) Phenylalanine hydroxylase
C) Homogentisate oxidase
D) Arginase
✅ Answer: C) Homogentisate oxidase
Explanation: Deficiency causes homogentisic acid accumulation → black urine.
Q75. Maple syrup urine disease is due to defect in metabolism of:
A) Aromatic amino acids
B) Branched-chain amino acids
C) Sulfur amino acids
D) Basic amino acids
✅ Answer: B) Branched-chain amino acids
Explanation: Defective branched-chain α-keto acid dehydrogenase → BCAA accumulation.
🔬 Biochemistry MCQs – Part 4 (Q76–Q100)
Q76. Which vitamin is a cofactor for transketolase in the pentose phosphate pathway?
A) Niacin
B) Thiamine (Vitamin B1)
C) Riboflavin
D) Biotin
✅ Answer: B) Thiamine (B1)
Explanation: Transketolase requires thiamine pyrophosphate (TPP) as a coenzyme.
Q77. Pellagra is caused by deficiency of:
A) Thiamine
B) Niacin (Vitamin B3)
C) Riboflavin
D) Folic acid
✅ Answer: B) Niacin
Explanation: Niacin deficiency → dermatitis, diarrhea, dementia (“3 Ds”).
Q78. Beriberi is due to deficiency of:
A) Vitamin B1
B) Vitamin B2
C) Vitamin B3
D) Vitamin B6
✅ Answer: A) Vitamin B1 (Thiamine)
Explanation: Thiamine deficiency impairs carbohydrate metabolism → neurological + cardiac symptoms.
Q79. The vitamin required for synthesis of coenzyme A is:
A) Pantothenic acid (B5)
B) Biotin (B7)
C) Folate (B9)
D) Vitamin B12
✅ Answer: A) Pantothenic acid
Explanation: Pantothenic acid is a component of CoA.
Q80. Megaloblastic anemia is caused by deficiency of:
A) Vitamin B12 or Folate
B) Vitamin C
C) Vitamin D
D) Vitamin K
✅ Answer: A) B12 or Folate
Explanation: Both are essential for DNA synthesis in RBC precursors.
Q81. Scurvy is caused by deficiency of:
A) Vitamin A
B) Vitamin C
C) Vitamin D
D) Vitamin E
✅ Answer: B) Vitamin C
Explanation: Vitamin C deficiency impairs collagen synthesis → bleeding gums, poor wound healing.
Q82. Rickets in children is caused by deficiency of:
A) Vitamin C
B) Vitamin D
C) Vitamin E
D) Vitamin K
✅ Answer: B) Vitamin D
Explanation: Vitamin D deficiency → defective bone mineralization.
Q83. Vitamin K deficiency results in:
A) Night blindness
B) Bleeding disorders
C) Muscle weakness
D) Rickets
✅ Answer: B) Bleeding disorders
Explanation: Vitamin K needed for clotting factor synthesis (II, VII, IX, X).
Q84. The major antioxidant vitamin is:
A) Vitamin A
B) Vitamin D
C) Vitamin E
D) Vitamin K
✅ Answer: C) Vitamin E
Explanation: Vitamin E protects membranes against oxidative damage.
Q85. The enzyme inhibited by statins is:
A) Hexokinase
B) HMG-CoA reductase
C) Acetyl-CoA carboxylase
D) Pyruvate kinase
✅ Answer: B) HMG-CoA reductase
Explanation: Statins lower cholesterol by inhibiting HMG-CoA reductase.
Q86. The end product of purine metabolism in humans is:
A) Ammonia
B) Urea
C) Uric acid
D) Creatinine
✅ Answer: C) Uric acid
Explanation: Purines are degraded to uric acid, excreted in urine.
Q87. Lesch–Nyhan syndrome is due to deficiency of:
A) HGPRT enzyme
B) Adenosine deaminase
C) Glucose-6-phosphatase
D) Ornithine transcarbamylase
✅ Answer: A) HGPRT
Explanation: Deficiency in HGPRT → purine salvage defect → uric acid accumulation.
Q88. The enzyme deficient in severe combined immunodeficiency (SCID) is:
A) Adenosine deaminase
B) HGPRT
C) Glucose-6-phosphatase
D) G6PD
✅ Answer: A) Adenosine deaminase
Explanation: ADA deficiency → toxic dATP accumulation → impaired lymphocyte function.
Q89. The first nucleotide formed in de novo purine synthesis is:
A) AMP
B) GMP
C) IMP
D) UMP
✅ Answer: C) IMP (inosine monophosphate)
Explanation: IMP is the precursor for AMP and GMP.
Q90. The first nucleotide formed in pyrimidine synthesis is:
A) UMP
B) CMP
C) TMP
D) IMP
✅ Answer: A) UMP
Explanation: Pyrimidine synthesis forms UMP first → CMP, TMP.
Q91. The enzyme ribonucleotide reductase converts:
A) dNTPs → NTPs
B) NDPs → dNDPs
C) dNMPs → NMPs
D) ATP → cAMP
✅ Answer: B) NDPs → dNDPs
Explanation: It converts ribonucleotides to deoxyribonucleotides for DNA synthesis.
Q92. The main enzyme of DNA repair that removes RNA primers is:
A) DNA polymerase I
B) DNA polymerase III
C) Ligase
D) Helicase
✅ Answer: A) DNA polymerase I
Explanation: DNA pol I removes primers with 5′→3′ exonuclease activity.
Q93. The enzyme telomerase carries its own:
A) Protein only
B) RNA template
C) DNA template
D) Ribosome
✅ Answer: B) RNA template
Explanation: Telomerase extends telomeres using an RNA template.
Q94. The energy used in protein synthesis for peptide bond formation comes from:
A) ATP
B) GTP
C) FADH₂
D) NADH
✅ Answer: B) GTP
Explanation: Peptidyl transferase uses GTP in elongation.
Q95. The amino acid that starts protein synthesis in eukaryotes is:
A) Glycine
B) Alanine
C) Methionine
D) Serine
✅ Answer: C) Methionine
Explanation: Initiation codon AUG = methionine (Met).
Q96. The post-translational modification of insulin involves:
A) Hydroxylation
B) Phosphorylation
C) Cleavage of proinsulin
D) Methylation
✅ Answer: C) Cleavage of proinsulin
Explanation: Insulin synthesized as proinsulin → cleaved to active insulin + C-peptide.
Q97. The bond linking nucleotides in DNA is:
A) Hydrogen bond
B) Phosphodiester bond
C) Peptide bond
D) Glycosidic bond
✅ Answer: B) Phosphodiester bond
Explanation: DNA backbone held by phosphodiester bonds between sugars and phosphates.
Q98. The amino acid precursor of catecholamines (dopamine, norepinephrine, epinephrine) is:
A) Phenylalanine
B) Tryptophan
C) Histidine
D) Glycine
✅ Answer: A) Phenylalanine
Explanation: Phenylalanine → Tyrosine → DOPA → dopamine → NE → epinephrine.
Q99. The amino acid precursor of histamine is:
A) Glycine
B) Histidine
C) Serine
D) Tyrosine
✅ Answer: B) Histidine
Explanation: Histidine decarboxylated to histamine.
Q100. The amino acid precursor of GABA is:
A) Glutamate
B) Aspartate
C) Alanine
D) Tryptophan
✅ Answer: A) Glutamate
Explanation: Glutamate decarboxylated to GABA (major inhibitory neurotransmitter).
Biochemistry MCQs with explanations, solved biochemistry multiple choice questions for NEET, CBSE ICSE objective biochemistry questions, biochemistry MCQs for CUET and CSIR NET, important biochemistry questions for GATE and DBT BET JRF, biochemistry multiple choice questions for USMLE and PLAB, practice biochemistry MCQs for AMC licensing exams, solved biochemistry questions for SAT Biology Subject Test, GRE Biology Subject Test biochemistry MCQs, biochemistry multiple choice questions for BMAT and IMAT exams
