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DNA, genes and protein synthesis: exam questions

6 questions, 18 marks. Write your answers on paper, then open each mark scheme.

Spec 3.14–3.18BQuestions and mark scheme (PDF)3 pages

Question 1

Which statement correctly describes a gene?

  1. The entire DNA of an organism
  2. A section of a DNA molecule that codes for a specific protein
  3. A structure in the nucleus made of many chromosomes
  4. A single base in a DNA molecule
[1 mark]
Show mark scheme for question 1

Answer: B (1)

Question 2

Describe how genes, chromosomes and the nucleus are related.

[3 marks]
Show mark scheme for question 2
  • the nucleus contains chromosomes (1)
  • genes are located on the chromosomes (1)
  • each gene is a section of DNA that codes for a specific protein (1)
  • allow chromosomes are made of DNA / one long DNA molecule

Question 3

In a human body cell, where are chromosomes found?

  1. Ribosomes
  2. Cell membrane
  3. Nucleus
  4. Mitochondria
[1 mark]
Show mark scheme for question 3

Answer: C (1)

Question 4

Biology only (what this means)Biology only: only in International GCSE Biology. Double Award students can skip it. What the labels mean

A section of one strand of a DNA molecule has the base sequence A T T G C A. (a) Write the base sequence of the complementary strand. (1) (b) Describe the structure of a DNA molecule. (2)

[3 marks]
Show mark scheme for question 4
  • T A A C G T (1)
  • two strands coiled to form a double helix (1)
  • strands linked by (a series of) paired bases (1)
  • allow A with T and C with G for the third marking point

Question 5

Biology only (what this means)Biology only: only in International GCSE Biology. Double Award students can skip it. What the labels mean

The template strand of a gene has the base sequence T A C C T T G C A. (a) Write the sequence of mRNA that is made from this gene. (2) (b) State the anticodons of the tRNA molecules that pair with the first two codons. (2)

[4 marks]
Show mark scheme for question 5
  • first codon A U G (1)
  • second and third codons G A A C G U (1)
  • first anticodon UAC (1)
  • second anticodon CUU (1)
  • allow ecf from (a)

Question 6

Biology only (what this means)Biology only: only in International GCSE Biology. Double Award students can skip it. What the labels mean

Describe how the information in a gene is used to make a protein. In your answer, include the roles of mRNA, ribosomes, tRNA, codons and anticodons.

[6 marks]
Show mark scheme for question 6
LevelMarksWhat the answer does
35–6A clear, correct and well-organised account of both transcription and translation, in the right order, using most of the terms (mRNA, ribosome, tRNA, codon, anticodon) accurately.
23–4A mostly correct account of both stages, or a detailed account of one stage, with some of the terms used. Some steps may be missing or out of order.
11–2A few relevant points, for example that mRNA carries a copy of the gene to a ribosome. Little detail or sequencing.

Indicative content

  • transcription in the nucleus: a copy of the gene is made as mRNA (single strand, complementary bases, U instead of T)
  • mRNA leaves the nucleus and attaches to a ribosome
  • mRNA is read in codons, groups of three bases, each coding for one amino acid
  • tRNA molecules each carry a specific amino acid to the ribosome
  • the anticodon of tRNA pairs with the complementary codon on mRNA
  • amino acids are joined in order to make a polypeptide, which folds to form a protein
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