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CAIE A-Level Biology AS 6.1 Structure of Nucleic Acids and Dna Replication Questions

Practise CAIE AS Biology 6.1 by interpreting nucleotide and DNA structures, comparing RNA with DNA, and tracing semi-conservative DNA replication.

Syllabus
2028–2030
Course
Biology 9700
Level
AS

Exam points

  • Describe nucleotide structure, including the sugar, phosphate and nitrogenous base in ATP and nucleic-acid nucleotides.
  • Distinguish purines from pyrimidines by their ring structures and identify the bases found in DNA and RNA.
  • Interpret DNA double-helix structure, including antiparallel complementary base pairing, hydrogen bonds and phosphodiester bonds.
  • Explain semi-conservative DNA replication, including DNA polymerase, ligase, leading and lagging strands, and 5′ to 3′ synthesis.
  • Describe RNA structure using mRNA and compare RNA nucleotides with those in DNA.

Covered syllabus points

6.1.1—Nucleotide structure6.1.2—Purines (adenine, guanine)6.1.3—Pyrimidines (cytosine, thymine, uracil)6.1.4—DNA double helix structure6.1.5—Semi-conservative DNA replication6.1.6—RNA (mRNA) structure

Question 1

[Maximum number: 1]

Which statements are correct for all nucleotides?

1 The nitrogen-containing base is always attached to carbon atom 1 of the pentose.
2 The phosphate group is always attached to carbon atom 5 of the pentose.
3 A condensation reaction occurs to join the nitrogen-containing base to the pentose.
4 Nucleotides are linked together by condensation reactions between phosphate groups.

A

1, 2 and 3

B

1 and 2 only

C

1, 3 and 4

D

2, 3 and 4

Question 2

[Maximum number: 1]

Which row represents the correct features of guanine?

has a single ring structure

is a purine

joins its complementary base via three hydrogen bonds

pairs with thymine

key

✓ = correct

χ=\boldsymbol{\chi}= not correct

✓

✓

χ\boldsymbol{\chi}

✓

✓

χ\boldsymbol{\chi}

✓

χ\boldsymbol{\chi}

x

✓

✓

×\boldsymbol{\times}

χ\boldsymbol{\chi}

χ\boldsymbol{\chi}

✓

✓

Question 3

[Maximum number: 1]

The diagrams show the chemical structure of four bases.

1

1

2

2

3

3

4

4

Which diagrams show thymine and cytosine?

A

1 and 2

B

1 and 4

C

2 and 3

D

3 and 4

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