A cell in the pancreas produces the protein insulin. Describe the roles of DNA, messenger RNA (mRNA) and ribosomes in producing the insulin protein, starting from the gene in the nucleus.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Insulin is a protein hormone made up of a specific sequence of amino acids. It is produced in specialised cells of the pancreas and released into the blood to regulate blood glucose concentration.
Model answer (5 marks)
The gene in the nucleus contains the DNA sequence that codes for insulin.
The DNA sequence is transcribed into a complementary mRNA strand.
The mRNA exits the nucleus and binds to a ribosome in the cytoplasm.
The ribosome reads the mRNA codons, each codon specifying a particular amino acid.
The ribosome links the amino acids in the correct order to form the insulin protein.
The DNA sequence is transcribed into a complementary mRNA strand.
The mRNA exits the nucleus and binds to a ribosome in the cytoplasm.
The ribosome reads the mRNA codons, each codon specifying a particular amino acid.
The ribosome links the amino acids in the correct order to form the insulin protein.
Examiner tips
- Use the word ‘transcription’ for DNA to mRNA, ‘translation’ for mRNA to protein.
- Show the flow: gene → mRNA → ribosome → protein.
- Mention codons and amino acid sequence.
- Keep each point short and to the point.
Common mistakes
- Confusing transcription with translation or vice versa.
- Omitting the ribosome’s role in reading codons.
- Not stating that the mRNA leaves the nucleus.
Mark scheme (5 marks)
- The gene (section of DNA) contains a sequence of bases that codes for the insulin protein
- The base sequence of the gene is used as a template to make a complementary strand of mRNA (transcription)
- The mRNA moves out of the nucleus to a ribosome in the cytoplasm
- The ribosome reads the mRNA base sequence in groups of three bases (codons) / each codon codes for a specific amino acid
- Amino acids are joined together in a specific sequence to form the insulin protein (translation)
Key terms in this question
gene · DNA · messenger RNA (mRNA) · ribosome
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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