Explain why two different types of human cell, such as a liver cell and a muscle cell, can contain the same genes yet produce different proteins.

Cambridge International IGCSE Biology (0610) — 17.1 Chromosomes, genes and proteins · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

All human cells contain the same genes, i.e. the same DNA sequence.
Only certain genes are switched on (expressed) in a given cell type.
A gene codes for the sequence of amino acids in a specific protein.
Because different genes are switched on in different cell types, different amino‑acid sequences are assembled at ribosomes, producing different proteins.

Examiner tips

  • Use the word "expressed" to show understanding of gene regulation.
  • Show the link from DNA → RNA → protein to justify protein differences.
  • Mention that the same DNA can give different proteins via selective gene expression.

Common mistakes

  • Confusing DNA with RNA or proteins; not explaining the role of gene expression.
  • Failing to state that all cells have the same genes; implying genetic differences.
  • Using vague terms like "different" without linking to gene activation.

Mark scheme (4 marks)

  1. All (body/diploid) cells contain the same genes / same DNA / same genetic information
  2. Only certain genes are switched on (expressed) in a given cell type
  3. A gene codes for / determines the sequence of amino acids in a specific protein
  4. Different genes switched on in different cell types means different sequences of amino acids are assembled at ribosomes, producing different proteins

Key terms in this question

gene

Related

More Chromosomes, genes and proteins questions

▶ Try answering this question with AI marking (free) →