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Protein synthesis and gene variants: exam questions

5 questions, 14 marks. Write your answers on paper, then open each mark scheme.

Spec 3.7B–3.10B
Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean
Questions and mark scheme (PDF)3 pages

Question 1

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean

What decides the order of amino acids in a protein?

  1. The shape of the ribosome
  2. The order of bases in a gene
  3. The number of chromosomes in the cell
  4. The type of enzyme in the nucleus
[1 mark]
Show mark scheme for question 1

Answer: B – The order of bases in a gene (1)

Question 2

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean

Explain how the order of bases in a gene decides the shape of an enzyme.

[3 marks]
Show mark scheme for question 2
  • the order of bases decides the order of amino acids (1)
  • the chain of amino acids folds (1)
  • to produce a specifically shaped protein / active site (1)

Question 3

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean

Describe how a gene is used to make a polypeptide.

[4 marks]
Show mark scheme for question 3
  • RNA polymerase binds to non-coding DNA in front of the gene (1)
  • RNA polymerase produces a complementary mRNA strand (1)
  • from the coding DNA of the gene (1)
  • mRNA attaches to a ribosome (1)
  • codons / triplets of bases in the mRNA code for specific amino acids (1)
  • tRNA transfers amino acids to the ribosome (1)
  • amino acids are linked to form a polypeptide (1)
  • Max 4

Question 4

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean

A variant in the non-coding DNA in front of a gene alters the phenotype of an organism. The protein made from the gene has the same sequence of amino acids. Explain how the variant can affect the phenotype.

[3 marks]
Show mark scheme for question 4
  • the variant affects the binding of RNA polymerase (1)
  • so a different amount of mRNA is made (1)
  • so the quantity of protein produced is altered (1)

Question 5

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean
Higher tier (what this means)Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean

A variant in the coding DNA of a gene for an enzyme stops the enzyme working. Explain how.

[3 marks]
Show mark scheme for question 5
  • the sequence of amino acids is altered (1)
  • so the protein folds into a different shape / the active site changes shape (1)
  • the substrate no longer fits so the enzyme activity is reduced or lost (1)
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