DNA structure (biology only) - AQA GCSE Biology Exam Questions

Practise 30 exam-style questions on DNA structure (biology only) for AQA GCSE Biology. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

30 questions
1–4 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

1 mark

Where in the cell are proteins synthesised?

Model answer

Ribosomes

Explanation

Proteins are assembled at ribosomes in the cytoplasm (or on the rough endoplasmic reticulum).

Mark scheme

1 mark
ribosome(s)

Question 2

2 marks

Name the three parts of a DNA nucleotide.

Model answer

A sugar (deoxyribose), a phosphate group and a base attached to the sugar.

Explanation

Each nucleotide contains a common sugar and phosphate backbone with one of four bases attached to the sugar.

Mark scheme

1 mark
sugar (deoxyribose)
1 mark
phosphate group or base
Any two of the three parts earn 2 marks; list may include base as one mark.

Question 3

3 marks

Explain why complementary base pairing is important for accurate DNA replication.

Model answer

Because each base only pairs with its specific partner (A with T, C with G), each strand can act as a template to make a matching complementary strand so the sequence is copied accurately.

Explanation

Specific pairing ensures that when the two strands separate, new nucleotides line up against the exposed bases to produce an accurate copy of the original DNA.

Mark scheme

1 mark
each base pairs with a specific partner (A with T, C with G)
1 mark
each original strand acts as a template
1 mark
so the new strand is complementary and the sequence is copied accurately

Question 4

4 marks

Give a simple description of protein synthesis suitable for a GCSE answer.

Model answer

The DNA sequence is used as a template to make a molecule that carries the code (transcription). This code is read at ribosomes; carrier molecules bring specific amino acids and the amino acids are joined in the correct order to make the protein (translation).

Explanation

A simplified account describes the two main stages: a template from DNA and the assembly of amino acids on ribosomes in the correct sequence to form a protein.

Mark scheme

1 mark
DNA is used as a template to make a code (transcription)
Allow 'a molecule carrying the code' (no need to name mRNA at foundation).
1 mark
proteins are synthesised on ribosomes
1 mark
carrier molecules bring specific amino acids
Do not penalise use of term 'carrier molecules'.
1 mark
amino acids joined in correct order to make protein

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