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CAIE A-Level Biology 6.2.6 Gene Mutations and Base Sequences

Practise tracing a changed DNA base sequence through mRNA codons to possible amino-acid and protein effects while recognising silent or non-coding outcomes.

Syllabus
2028–2030
Course
Biology 9700
Level
AS

Exam points

  • identify a gene mutation from an altered DNA nucleotide or base-pair sequence
  • trace a changed DNA triplet through mRNA codon to a possible amino-acid change
  • recognise that not every gene mutation changes a polypeptide or its function

6.2.6—Gene mutations question 1

[Maximum number: 2]

Smooth muscle is a tissue composed of smooth muscle cells. The cells contain cytoplasm packed with proteins that are involved in contraction and relaxation.

Caldesmon is a large protein with a number of binding sites to attach to other proteins.

Caldesmon exists in two different forms, H-caldesmon and L-caldesmon.
H-caldesmon helps to regulate contraction and relaxation in smooth muscle cells.
L -caldesmon is found in some non-muscle cells, where it also acts as a regulatory protein.
- Caldesmon is coded for by a gene known as CALD1.
- CALD1 has 17 exons.
- The primary structure of H-caldesmon has a repeating sequence in the middle of the amino acid chain that is not present in L-caldesmon.

Researchers have discovered that a gene mutation is not the cause of the two different forms of caldesmon.

Explain what is meant by a gene mutation.

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