A research team is studying how muscle cells in an athlete produce large amounts of myosin, a structural protein needed for muscle contraction. Describe how the genetic information in a cell leads to the production of myosin, starting from the DNA in the nucleus.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Myosin is a protein made up of a specific sequence of amino acids. It is encoded by a gene found on one of the chromosomes inside muscle cell nuclei.
Model answer (5 marks)
A gene is a section of DNA that codes for a specific amino‑acid sequence – the myosin gene encodes the sequence of myosin. The DNA is transcribed in the nucleus to produce a messenger RNA (mRNA) copy. The mRNA carries the genetic information from the nucleus to the ribosomes in the cytoplasm. At the ribosome the mRNA is translated, with tRNA bringing the appropriate amino acids. The amino acids are joined together in the order specified by the mRNA to form the myosin protein, whose specific sequence determines its structure and function.
Examiner tips
- Use the exact terms ‘gene’, ‘transcription’, ‘mRNA’, ‘translation’, ‘ribosome’, ‘amino‑acid sequence’.
- Show the flow: DNA → mRNA → ribosome → protein.
- Mention that the sequence determines structure and function.
Mark scheme (5 marks)
- A gene is a section of DNA that codes for a specific amino acid sequence / the myosin gene codes for the specific amino acid sequence of myosin
- The DNA / gene is transcribed and a copy is made as mRNA (messenger RNA) in the nucleus
- The mRNA carries the genetic information from the nucleus to the ribosomes
- At the ribosome, the mRNA sequence is translated into an amino acid sequence
- The amino acids are joined together in a specific sequence to form the protein myosin / the specific sequence of amino acids determines the structure and function of the protein
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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