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Nucleic Acids (Biomolecules) — WBJEE Practice

WBJEE-focused MCQs on nucleic acids with answers, explanations, essential revision notes and related mock tests to aid chapter practice and exam preparation.

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Biomolecules (Nucleic Acids) Revision Guide for WBJEE Chemistry

Biomolecules (Nucleic Acids) is part of WBJEE Chemistry preparation. A strong revision plan should combine concept review with exam-style questions so that definitions, relationships, calculations and exceptions are recalled accurately.

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  • Important equations or relationships
  • Common applications and examples
  • Frequently confused concepts
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  • Error review and targeted revision

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Top 20 Biomolecules (Nucleic Acids) MCQs with Answers

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WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

1. DNA stands for:

  • A. Deoxyribose nitrogen acid
  • B. Dinucleic acid
  • C. Deoxyribonucleic acid
  • D. Dihydroxyribonucleic acid
Answer: C
Explanation: DNA is deoxyribonucleic acid.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

2. RNA stands for:

  • A. Reactive nucleic acid
  • B. Ribonucleic acid
  • C. Reduced nucleic acid
  • D. Ribose nitrogen acid
Answer: B
Explanation: RNA is ribonucleic acid.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

3. The pentose sugar in DNA is:

  • A. 2-Deoxyribose
  • B. Ribose
  • C. Glucose
  • D. Fructose
Answer: A
Explanation: DNA contains 2-deoxy-D-ribose.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

4. The pentose sugar in RNA is:

  • A. 2-Deoxyribose
  • B. Glucose
  • C. Galactose
  • D. Ribose
Answer: D
Explanation: RNA contains ribose.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

5. A nucleotide contains:

  • A. Sugar and amino acid
  • B. Base and fatty acid
  • C. Nitrogenous base, pentose sugar and phosphate
  • D. Base and sugar only
Answer: C
Explanation: A nucleotide is a phosphorylated nucleoside.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

6. A nucleoside contains:

  • A. Sugar and amino acid
  • B. Nitrogenous base and pentose sugar
  • C. Base, sugar and phosphate
  • D. Phosphate only
Answer: B
Explanation: A nucleoside consists of a base linked to a pentose sugar.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

7. Which pair consists only of purine bases?

  • A. Adenine and guanine
  • B. Cytosine and thymine
  • C. Thymine and uracil
  • D. Cytosine and uracil
Answer: A
Explanation: Adenine and guanine are purines.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

8. Which base is a pyrimidine?

  • A. Adenine
  • B. Guanine
  • C. Both adenine and guanine
  • D. Cytosine
Answer: D
Explanation: Cytosine is a pyrimidine base.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

9. The base present in DNA but normally absent from RNA is:

  • A. Adenine
  • B. Guanine
  • C. Thymine
  • D. Uracil
Answer: C
Explanation: DNA normally contains thymine instead of uracil.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

10. The base present in RNA in place of thymine is:

  • A. Cytosine
  • B. Uracil
  • C. Guanine
  • D. Adenine
Answer: B
Explanation: RNA normally contains uracil.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

11. In Watson-Crick DNA base pairing, adenine pairs with:

  • A. Thymine
  • B. Guanine
  • C. Cytosine
  • D. Uracil
Answer: A
Explanation: Adenine pairs with thymine in DNA.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

12. In double-stranded DNA, guanine pairs with:

  • A. Adenine
  • B. Thymine
  • C. Uracil
  • D. Cytosine
Answer: D
Explanation: Guanine pairs specifically with cytosine.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

13. An A-T base pair is stabilised by:

  • A. One covalent bond
  • B. Four hydrogen bonds
  • C. Two hydrogen bonds
  • D. Three hydrogen bonds
Answer: C
Explanation: Adenine and thymine form two hydrogen bonds.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

14. A G-C base pair is stabilised by:

  • A. Four ionic bonds
  • B. Three hydrogen bonds
  • C. Two hydrogen bonds
  • D. One hydrogen bond
Answer: B
Explanation: Guanine and cytosine form three hydrogen bonds.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

15. The backbone of a nucleic-acid chain is mainly:

  • A. Sugar-phosphate
  • B. Base-base
  • C. Peptide
  • D. Fatty acid-glycerol
Answer: A
Explanation: Alternating pentose and phosphate groups form the backbone.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

16. Adjacent nucleotides in one nucleic-acid strand are linked by:

  • A. Peptide bonds
  • B. Disulfide bonds
  • C. Hydrogen bonds only
  • D. Phosphodiester bonds
Answer: D
Explanation: 3'-5' phosphodiester linkages connect nucleotides.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

17. The nitrogenous base is attached to pentose sugar through a:

  • A. Disulfide bond
  • B. Phosphodiester bond
  • C. N-glycosidic bond
  • D. Peptide bond
Answer: C
Explanation: A beta-N-glycosidic bond links the base to C1' of the sugar.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

18. The two strands of typical DNA are:

  • A. Identical in sequence
  • B. Antiparallel
  • C. Parallel in the same direction
  • D. Covalently cross-linked throughout
Answer: B
Explanation: One strand runs 5'→3' while the complementary strand runs 3'→5'.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

19. Complementary DNA strands are held together mainly by:

  • A. Hydrogen bonds between bases
  • B. Peptide bonds
  • C. Metallic bonds
  • D. Disulfide bonds
Answer: A
Explanation: Hydrogen bonding between complementary bases stabilises the duplex.

WBJEE Chemistry · Biomolecules (Nucleic Acids) · Very Very Hard

20. If one DNA strand contains 5'-ATGC-3', the complementary strand written antiparallel is:

  • A. 3'-ATGC-5'
  • B. 5'-TACG-3' only as antiparallel notation
  • C. 3'-UACG-5'
  • D. 3'-TACG-5'
Answer: D
Explanation: A pairs with T and G with C, with opposite strand polarity.

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