A student is investigating how proteins are made in a cell. Explain how the sequence of bases in a gene determines the structure of a specific protein, including the roles of transcription and translation in this process.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Proteins are made by cells following instructions stored in the DNA. The process involves two key stages that take place in different parts of the cell.
Model answer (5 marks)
A gene is a DNA segment that encodes a specific amino‑acid sequence.
During transcription the DNA double helix is opened and an RNA polymerase synthesises a complementary mRNA strand in the nucleus.
The mRNA is transported to the cytoplasm and binds to a ribosome.
During translation the ribosome reads the mRNA codons and matches each with the appropriate tRNA carrying an amino acid.
The amino acids are joined in the order dictated by the mRNA to form a protein with a defined structure and function.
During transcription the DNA double helix is opened and an RNA polymerase synthesises a complementary mRNA strand in the nucleus.
The mRNA is transported to the cytoplasm and binds to a ribosome.
During translation the ribosome reads the mRNA codons and matches each with the appropriate tRNA carrying an amino acid.
The amino acids are joined in the order dictated by the mRNA to form a protein with a defined structure and function.
Examiner tips
- Use the exact terms ‘gene’, ‘transcription’, ‘mRNA’, ‘translation’, ‘ribosome’, ‘amino acid’, ‘protein’.
- Show the flow: DNA → mRNA → ribosome → protein.
- Mention the nucleus for transcription and cytoplasm for translation.
- Include that the mRNA codon sequence determines the amino‑acid order.
Common mistakes
- Confusing DNA with RNA or omitting the nucleus/cytoplasm locations.
- Using vague phrases like ‘copy’ instead of ‘mRNA’ or ‘transcription’.
- Failing to state that the ribosome joins amino acids in the correct order.
Mark scheme (5 marks)
- A gene is a section of DNA that codes for a specific amino acid sequence
- During transcription, the DNA is unzipped and a copy is made as mRNA in the nucleus
- The mRNA carries the genetic information from the nucleus to the ribosomes
- During translation, the mRNA sequence is used to join amino acids in the correct order at the ribosome
- The amino acids are polymerised to form a specific protein with a particular structure/function
Key terms in this question
gene · transcription · translation
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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