OCR A Level Biology:复习笔记2.3.8 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

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

The translation stage of protein synthesis – an amino acid chain is formed