OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(g) transcription and translation of genes resulting in the synthesis of…
Full specification wording
Nucleotides and nucleic acids: (g) transcription and translation of genes resulting in the synthesis of polypeptides.
Transcription makes a messenger RNA copy of a gene in the nucleus.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 8 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Transcription makes a messenger RNA copy of a gene in the nucleus. DNA helicase unwinds the double helix, and RNA polymerase joins free RNA nucleotides to the template strand by complementary base pairing (adenine pairs with uracil in RNA). The mRNA strand is formed, then leaves the nucleus through a nuclear pore to a ribosome. Translation occurs at the ribosome: tRNA molecules carry specific amino acids and their anticodons pair with complementary mRNA codons. A start codon begins translation, and a stop codon ends it. Peptide bonds form between adjacent amino acids, building a polypeptide whose sequence is determined by the order of codons.
What earns the marks
- Transcription: DNA helicase unwinds the double helix and RNA polymerase joins free RNA nucleotides to the template strand by complementary base pairing.
- In RNA, adenine pairs with uracil, so the mRNA sequence is complementary to the DNA template.
- mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome.
- Translation: tRNA molecules carry specific amino acids, and their anticodons pair with complementary mRNA codons.
- A start codon initiates translation and a stop codon terminates it.
- Peptide bonds form between adjacent amino acids, producing a polypeptide whose sequence is set by the codon order.
Common mistakes and how to put them right
Saying thymine pairs with adenine during transcription.
Put it right by stating uracil pairs with adenine in RNA.
Confusing the template and coding strands.
Put it right: The mRNA is complementary to the template strand, not identical to it.
Describing translation as occurring in the nucleus.
Put it right: State that mRNA moves to a ribosome in the cytoplasm for translation.
Exam tips
- Sequence the stages clearly: unwinding, complementary base pairing, mRNA formation, movement to ribosome, codon–anticodon pairing, peptide bond formation.
- Use the terms template strand, anticodon and codon precisely to gain credit.
- Link the final polypeptide sequence to the order of mRNA codons.
Try the lesson
The start of the Nucleotides and nucleic acids: (g) transcription and translation of genes resulting in the synthesis of polypeptides. lesson, made from checked teaching notes for this specification point.
Have a go first
During transcription, which enzyme forms phosphodiester bonds between adjacent RNA nucleotides?
Listen
Transcription makes a messenger RNA copy of a gene in the nucleus. DNA helicase unwinds the double helix, and RNA polymerase joins free RNA nucleotides to the template strand by complementary base pairing (adenine pairs with uracil in RNA). The mRNA strand is formed, then leaves the nucleus through a nuclear pore to a ribosome. Translation occurs at the ribosome: tRNA molecules carry specific amino acids and their anticodons pair with complementary mRNA codons. A start codon begins translation, and a stop codon ends it. Peptide bonds form between adjacent amino acids, building a polypeptide whose sequence is determined by the order of codons. A strong answer earns marks for these points. Transcription: DNA helicase unwinds the double helix and RNA polymerase joins free RNA nucleotides to the template strand by complementary base pairing. In RNA, adenine pairs with uracil, so the mRNA sequence is complementary to the DNA template. mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome. Translation: tRNA molecules carry specific amino acids, and their anticodons pair with complementary mRNA codons. A common slip: Saying thymine pairs with adenine during transcription. Instead, stating uracil pairs with adenine in RNA. Exam tip: Sequence the stages clearly: unwinding, complementary base pairing, mRNA formation, movement to ribosome, codon–anticodon pairing, peptide bond formation.
Key words
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Transcription by RNA polymerase
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Complementary base pairing with uracil
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Translation at the ribosome
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Codon–anticodon pairing and peptide bond formation
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See every definition
- Transcription by RNA polymerase
- DNA helicase unwinds the double helix and RNA polymerase joins free RNA nucleotides to the template strand by complementary base pairing.
- Complementary base pairing with uracil
- In RNA, adenine pairs with uracil, so the mRNA sequence is complementary to the DNA template.
- Translation at the ribosome
- mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome, where tRNA molecules carry specific amino acids.
- Codon–anticodon pairing and peptide bond formation
- Anticodons pair with complementary mRNA codons, and peptide bonds form between adjacent amino acids, producing a polypeptide whose sequence is set by the codon order.
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