A level Biology B · Edexcel 9BI0 · Topic 1F
Protein synthesis and the genetic code
Key points
- A gene is a sequence of bases coding for a polypeptide. The genetic code is a triplet code, non-overlapping and degenerate (most amino acids have more than one codon), with start and stop codons.
- Transcription (in the nucleus): RNA polymerase makes a complementary mRNA copy of the template strand. In eukaryotes introns are removed by splicing, leaving the exons.
- Translation (at the ribosome): mRNA codons pair with anticodons on tRNA molecules, each carrying a specific amino acid.
- The ribosome moves along the mRNA, peptide bonds form between amino acids, and the process ends at a stop codon.
- Alternative splicing allows one gene to give several different proteins.
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A gene is only useful if the cell can read it. Protein synthesis turns a base sequence in DNA into a sequence of amino acids in two stages: transcription in the nucleus and translation at a ribosome.
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