OCR AS Biology

Revision Notes

2.3.8 Translation

Translation

  • Translation occurs in the cytoplasm of the cell
  • After leaving the nucleus via a nuclear pore, the mRNA molecule attaches to a ribosome
  • In the cytoplasm, there are free molecules of tRNA (transfer RNA)
  • These tRNA molecules have a triplet of unpaired bases at one end (known as the anticodon) and a region where a specific amino acid can attach at the other
    • There are about 20 different tRNA molecules, each with a specific anticodon and specific amino acid binding site
  • The tRNA molecules bind with their specific amino acids (also in the cytoplasm) and bring them to the mRNA molecule on the ribosome
  • The triplet of bases (anticodon) on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule
  • Two tRNA molecules fit onto the ribosome at any one time, bringing the amino acid they are each carrying side by side
  • A peptide bond is then formed (via a condensation reaction) between the two amino acids
  • This process continues until a ‘stop’ codon on the mRNA molecule is reached – this acts as a signal for translation to stop and at this point the amino acid chain coded for by the mRNA molecule is complete
  • The amino acid chain then forms the final polypeptide

_tRNA molecules bind with amino acids, downloadable AS & A Level Biology revision notes

The translation stage of protein synthesis – tRNA molecules bind with their specific amino acids.

Translation (1)_3, downloadable AS & A Level Biology revision notesTranslation (2), downloadable AS & A Level Biology revision notes
The translation stage of protein synthesis – an amino acid chain is formed.

Exam Tip

Make sure you learn both stages of protein synthesis fully. Don’t forget – transcription occurs in the nucleus but translation occurs in the cytoplasm!

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