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
Examiner 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!
