Edexcel A (SNAB) A Level Biology:复习笔记2.3.2 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)
  • tRNA is a single stranded molecule of RNA that folds into a clover-like structre
  • tRNA molecules have a triplet of unpaired bases at one end, known as the anticodon, and a region at the other end where a specific amino acid can attach
  • 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 on the mRNA molecule called the codon
  • Near the beginning of the mRNA is a triplet of bases called the start codon (AUG)
  • This is a signal to start off translation
  • AUG codes for an amino acid called methionine
• 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 process of translation