Page 1 of 120
CBSE BIOCHEM Exam Actual Test Questions and Correct
Answers With Rationales LATEST THIS YEAR
Biochemistry Core Topics (CBSE/Step 1 Alignment)
1. Protein Structure & Function: Amino acid classification (nonpolar, polar, acidic, basic),
primary/secondary/tertiary/quaternary structure, protein folding, denaturation, post-
translational modifications, collagen structure, hemoglobin/myoglobin (oxygen binding curves,
cooperativity, 2,3-BPG, Bohr effect)
2. Enzymes & Kinetics: Michaelis-Menten kinetics (Vmax, Km), Lineweaver-Burk plots, competitive
vs. noncompetitive inhibition, allosteric regulation, cofactors/coenzymes, zymogen activation,
isoenzymes (CK-MB, LDH, ALP)
3. Bioenergetics & Metabolism: ATP as energy currency, redox reactions (NADH, FADH₂),
glycolysis, gluconeogenesis, glycogenolysis/glycogenesis, pentose phosphate pathway (G6PD
deficiency), TCA cycle, oxidative phosphorylation (ETC complexes, ATP synthase, uncouplers,
inhibitors), fatty acid oxidation (carnitine shuttle, ketogenesis), fatty acid synthesis, cholesterol
synthesis, amino acid metabolism (urea cycle, transamination, one-carbon metabolism),
nucleotide synthesis (purines, pyrimidines)
4. Hormonal Regulation: Insulin, glucagon, cortisol, epinephrine (metabolic effects), thyroid
hormones, regulation of blood glucose, starvation/well-fed states
5. Nutrition & Vitamins: Water-soluble vitamins (B1, B2, B3, B5, B6, B7, B9, B12, C), fat-soluble
vitamins (A, D, E, K), deficiency diseases, coenzyme functions
6. Molecular Biology & Genetics: DNA replication, transcription, translation, mutations (point,
frameshift, nonsense, missense, silent), DNA repair mechanisms, regulation of gene expression
(operons, transcription factors, epigenetics), cancer biology (oncogenes, tumor suppressors,
p53, Rb)
7. Clinical Correlations: Metabolic disorders (PKU, alkaptonuria, von Gierke, Pompe, McArdle, Tay-
Sachs, Gaucher, Niemann-Pick, Lesch-Nyhan, OTC deficiency), porphyrias, amyloidosis, Wilson
disease, hemochromatosis, galactosemia, fructose intolerance, diabetic ketoacidosis (DKA),
lactic acidosis
1. Which amino acid contains an indole ring and is a precursor for serotonin?
A) Phenylalanine
B) Tyrosine
C) Tryptophan
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D) Histidine
Answer: C) Tryptophan
*Rationale: Tryptophan contains an indole ring and is the precursor for serotonin (5-hydroxytryptamine)
and melatonin. Phenylalanine and tyrosine are precursors for catecholamines; histidine is precursor for
histamine.*
2. A patient presents with homocystinuria, which can result from a defect in the metabolism of which
amino acid?
A) Methionine
B) Lysine
C) Leucine
D) Arginine
Answer: A) Methionine
Rationale: Homocystinuria is often due to cystathionine beta-synthase deficiency, leading to
accumulation of homocysteine (derived from methionine metabolism). Clinical features include
intellectual disability, lens dislocation, and thromboembolic events.
, Page 3 of 120
3. Which of the following amino acids is both ketogenic and glucogenic?
A) Leucine
B) Lysine
C) Isoleucine
D) Phenylalanine
Answer: C) Isoleucine
Rationale: Isoleucine is both ketogenic and glucogenic. Leucine and lysine are purely ketogenic;
phenylalanine is both glucogenic and ketogenic (converts to tyrosine).
4. A newborn with progressive neurological deterioration and a characteristic "maple syrup" odor in
urine likely has a defect in which metabolic pathway?
A) Urea cycle
B) Branched-chain amino acid metabolism
C) Phenylalanine hydroxylase
D) Tyrosine degradation
Answer: B) Branched-chain amino acid metabolism
Rationale: Maple syrup urine disease (MSUD) results from deficiency of branched-chain alpha-keto acid
, Page 4 of 120
dehydrogenase, causing accumulation of leucine, isoleucine, and valine, with urine odor resembling
maple syrup.
5. Which bond is primarily responsible for stabilizing alpha-helices in proteins?
A) Disulfide bonds
B) Hydrophobic interactions
C) Hydrogen bonds between amide hydrogens and carbonyl oxygens of residues four apart
D) Ionic bonds between side chains
Answer: C) Hydrogen bonds between amide hydrogens and carbonyl oxygens of residues four apart
*Rationale: Alpha-helices are stabilized by intrachain hydrogen bonds between the amide hydrogen of
residue n and the carbonyl oxygen of residue n+4.*
6. In the Lineweaver-Burk plot, competitive inhibition is characterized by which of the following
changes?
A) Increased Vmax, unchanged Km
B) Decreased Vmax, increased Km
C) Unchanged Vmax, increased Km
D) Unchanged Vmax, decreased Km
CBSE BIOCHEM Exam Actual Test Questions and Correct
Answers With Rationales LATEST THIS YEAR
Biochemistry Core Topics (CBSE/Step 1 Alignment)
1. Protein Structure & Function: Amino acid classification (nonpolar, polar, acidic, basic),
primary/secondary/tertiary/quaternary structure, protein folding, denaturation, post-
translational modifications, collagen structure, hemoglobin/myoglobin (oxygen binding curves,
cooperativity, 2,3-BPG, Bohr effect)
2. Enzymes & Kinetics: Michaelis-Menten kinetics (Vmax, Km), Lineweaver-Burk plots, competitive
vs. noncompetitive inhibition, allosteric regulation, cofactors/coenzymes, zymogen activation,
isoenzymes (CK-MB, LDH, ALP)
3. Bioenergetics & Metabolism: ATP as energy currency, redox reactions (NADH, FADH₂),
glycolysis, gluconeogenesis, glycogenolysis/glycogenesis, pentose phosphate pathway (G6PD
deficiency), TCA cycle, oxidative phosphorylation (ETC complexes, ATP synthase, uncouplers,
inhibitors), fatty acid oxidation (carnitine shuttle, ketogenesis), fatty acid synthesis, cholesterol
synthesis, amino acid metabolism (urea cycle, transamination, one-carbon metabolism),
nucleotide synthesis (purines, pyrimidines)
4. Hormonal Regulation: Insulin, glucagon, cortisol, epinephrine (metabolic effects), thyroid
hormones, regulation of blood glucose, starvation/well-fed states
5. Nutrition & Vitamins: Water-soluble vitamins (B1, B2, B3, B5, B6, B7, B9, B12, C), fat-soluble
vitamins (A, D, E, K), deficiency diseases, coenzyme functions
6. Molecular Biology & Genetics: DNA replication, transcription, translation, mutations (point,
frameshift, nonsense, missense, silent), DNA repair mechanisms, regulation of gene expression
(operons, transcription factors, epigenetics), cancer biology (oncogenes, tumor suppressors,
p53, Rb)
7. Clinical Correlations: Metabolic disorders (PKU, alkaptonuria, von Gierke, Pompe, McArdle, Tay-
Sachs, Gaucher, Niemann-Pick, Lesch-Nyhan, OTC deficiency), porphyrias, amyloidosis, Wilson
disease, hemochromatosis, galactosemia, fructose intolerance, diabetic ketoacidosis (DKA),
lactic acidosis
1. Which amino acid contains an indole ring and is a precursor for serotonin?
A) Phenylalanine
B) Tyrosine
C) Tryptophan
, Page 2 of 120
D) Histidine
Answer: C) Tryptophan
*Rationale: Tryptophan contains an indole ring and is the precursor for serotonin (5-hydroxytryptamine)
and melatonin. Phenylalanine and tyrosine are precursors for catecholamines; histidine is precursor for
histamine.*
2. A patient presents with homocystinuria, which can result from a defect in the metabolism of which
amino acid?
A) Methionine
B) Lysine
C) Leucine
D) Arginine
Answer: A) Methionine
Rationale: Homocystinuria is often due to cystathionine beta-synthase deficiency, leading to
accumulation of homocysteine (derived from methionine metabolism). Clinical features include
intellectual disability, lens dislocation, and thromboembolic events.
, Page 3 of 120
3. Which of the following amino acids is both ketogenic and glucogenic?
A) Leucine
B) Lysine
C) Isoleucine
D) Phenylalanine
Answer: C) Isoleucine
Rationale: Isoleucine is both ketogenic and glucogenic. Leucine and lysine are purely ketogenic;
phenylalanine is both glucogenic and ketogenic (converts to tyrosine).
4. A newborn with progressive neurological deterioration and a characteristic "maple syrup" odor in
urine likely has a defect in which metabolic pathway?
A) Urea cycle
B) Branched-chain amino acid metabolism
C) Phenylalanine hydroxylase
D) Tyrosine degradation
Answer: B) Branched-chain amino acid metabolism
Rationale: Maple syrup urine disease (MSUD) results from deficiency of branched-chain alpha-keto acid
, Page 4 of 120
dehydrogenase, causing accumulation of leucine, isoleucine, and valine, with urine odor resembling
maple syrup.
5. Which bond is primarily responsible for stabilizing alpha-helices in proteins?
A) Disulfide bonds
B) Hydrophobic interactions
C) Hydrogen bonds between amide hydrogens and carbonyl oxygens of residues four apart
D) Ionic bonds between side chains
Answer: C) Hydrogen bonds between amide hydrogens and carbonyl oxygens of residues four apart
*Rationale: Alpha-helices are stabilized by intrachain hydrogen bonds between the amide hydrogen of
residue n and the carbonyl oxygen of residue n+4.*
6. In the Lineweaver-Burk plot, competitive inhibition is characterized by which of the following
changes?
A) Increased Vmax, unchanged Km
B) Decreased Vmax, increased Km
C) Unchanged Vmax, increased Km
D) Unchanged Vmax, decreased Km
