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CAIE A-Level Biology 2.3.2 Protein Structure Levels

Practise distinguishing amino-acid sequence, α-helices or β-sheets, overall polypeptide folding and multi-subunit association across four protein-structure levels.

Syllabus
2028–2030
Course
Biology 9700
Level
AS

Exam points

  • identify primary structure from the specific order of amino acids in a polypeptide
  • recognise alpha-helices and beta-sheets as local forms of secondary structure
  • reserve quaternary structure for proteins containing two or more associated polypeptide chains

2.3.2—Protein structure levels question 1

[Maximum number: 1]

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.

Suggest how the two different forms of caldesmon can still have similar functions, even though they have a different primary structure.

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