AS & A Level Biology 9700 · Nucleic acids and protein synthesis · 6.1

Structure of nucleic acids: past paper questions

343 real questionsasked in 9 of the last 10 exam series2019–2025usually: Explain, State, Suggest, Describe, Complete

Real questions on structure of nucleic acids

The newest 20 of 343 written questions. Open one to see it on the real paper.

9700/21 · October/November 2025 · Q6a(i)[1]
State the term used to describe the sequence of nucleotides in the DNA of the alveolar macrophage that codes for a protein, such as lysozyme.
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9700/21 · October/November 2025 · Q6a(ii)[1]
Synthesis of lysozyme occurs in two stages. The first stage occurs in the nucleus using one strand of DNA to synthesise mRNA. State the name of the strand of DNA that is used to synthesise mRNA.
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9700/22 · October/November 2025 · Q3b[2]
With reference to the process of lactase synthesis, explain the relationship between: • • a transcribed strand and a primary transcript a primary transcript and messenger RNA (mRNA).
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9700/23 · October/November 2025 · Q4b(i)[2]
Complete Fig. 4.2 by drawing dotted lines to represent all the hydrogen bonds between the two strands of the DNA molecule.
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9700/23 · October/November 2025 · Q4b(ii)[1]
State the name of the bond X.
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9700/41 · October/November 2025 · Q1a(i)[2]
List all the possible genotypes of a guinea pig with short black fur.
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9700/41 · October/November 2025 · Q1a(ii)[1]
A test cross could be used to determine the genotype of a female guinea pig with short black fur. Describe the phenotype of the male guinea pig that could be used to carry out this test cross.
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9700/41 · October/November 2025 · Q1b[4]
A black guinea pig with long fur that was homozygous at both loci was crossed with a chocolate guinea pig with short fur that was homozygous at both loci. The F1 offspring of this cross had short black fur. F1 offspring were mated together to produce the F2 offspring. Complete the Punnett square to: show the cross betw...
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9700/41 · October/November 2025 · Q1c[2]
Some genes in guinea pigs are structural genes and some are regulatory genes. Describe the difference between a structural gene and a regulatory gene.
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9700/41 · October/November 2025 · Q2b(iii)[4]
Explain the genetic basis of the type of variation shown by the maize F2 generation.
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9700/41 · October/November 2025 · Q4a[3]
State the term used to describe: • an organism that has two copies of each gene • a form of a gene • a form of a gene that gives a phenotypic effect in a heterozygote. In addition to producing black coat colour, the protein coded for by the CPD103 gene also defends against infectious lung disease. Canine distemper viru...
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9700/42 · October/November 2025 · Q2a[3]
Explain the terms gene, genotype and phenotype. gene genotype phenotype
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9700/42 · October/November 2025 · Q2b[5]
A monohybrid genetic cross can be carried out to produce an F1 and an F2 generation. • • Outline how a monohybrid genetic cross is carried out. State the expected percentage of each of the different offspring genotypes in the F2 generation. Assume that the inheritance pattern is for autosomal dominant and recessive all...
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9700/42 · October/November 2025 · Q5d[4]
MLD is a rare autosomal recessive disease. It is estimated that there is one case of MLD in every 40 000 births worldwide. Children with MLD have a reduced life expectancy. • • MLD is a degenerative disease that causes severe disability. Before 2022, there was no known cure for MLD and the only treatment for symptoms w...
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9700/43 · October/November 2025 · Q1a(i)[2]
List all the possible genotypes of a guinea pig with short black fur.
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9700/43 · October/November 2025 · Q1a(ii)[1]
A test cross could be used to determine the genotype of a female guinea pig with short black fur. Describe the phenotype of the male guinea pig that could be used to carry out this test cross.
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9700/43 · October/November 2025 · Q1b[4]
A black guinea pig with long fur that was homozygous at both loci was crossed with a chocolate guinea pig with short fur that was homozygous at both loci. The F1 offspring of this cross had short black fur. F1 offspring were mated together to produce the F2 offspring. Complete the Punnett square to: show the cross betw...
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9700/43 · October/November 2025 · Q1c[2]
Some genes in guinea pigs are structural genes and some are regulatory genes. Describe the difference between a structural gene and a regulatory gene.
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9700/43 · October/November 2025 · Q2b(i)[2]
Explain how Fig. 2.1 can be used to determine which parent maize variety shows the greatest resistance to infection by E. turcicum.
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9700/43 · October/November 2025 · Q2b(ii)[1]
State the name of the type of variation shown by the maize F2 generation in Fig. 2.1.
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What examiners said

The majority of responses correctly identified most of the terms.
— Examiner report, February/March 2025, 9700/22 Q5(a) (Cambridge)

This was well answered, with most responses stating the correct term.
— Examiner report, February/March 2025, 9700/22 Q5(b)(i) (Cambridge)

Most responses provided the correct sequence of all six bases.
— Examiner report, February/March 2025, 9700/22 Q5(b)(iii) (Cambridge)

Practise this topic

Answer these questions online and get each one marked against the official mark scheme, with what you missed and how to fix it.

Practise structure of nucleic acids

In the syllabus

6.1 Structure of nucleic acids

describe the structure of nucleotides, including the phosphorylated nucleotide ATP (structural formulae are not expected)
state that the bases adenine and guanine are purines with a double ring structure, and that the bases cytosine, thymine and uracil are pyrimidines with a single ring structure (structural formulae for bases are not expected)
describe the structure of a DNA molecule as a double helix, including: • the importance of complementary base pairing between the 5′ to 3′ strand and the 3′ to 5′ strand (antiparallel strands) • differences in hydrogen bonding between C–G and A–T base pairs • linking of nucleotides by phosphodiester bonds
describe the semi-conservative replication of DNA during the S phase of the cell cycle, including: • the roles of DNA polymerase and DNA ligase (knowledge of other enzymes in DNA replication in cells and different types of DNA polymerase is not expected) • the differences between leading strand and lagging strand replication as a consequence of DNA polymerase adding nucleotides only in a 5′ to 3′ direction
describe the structure of an RNA molecule, using the example of messenger RNA (mRNA)

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