Translation is the second stage of protein synthesis: the mRNA base sequence is used to make a polypeptide with a specific amino acid sequence. It happens at a ribosome.
1. The mRNA binds to the small subunit of a ribosome, at the start codon AUG.
2. A tRNA with the complementary anticodon (UAC) pairs with the start codon by hydrogen bonds, bringing methionine.
3. A second tRNA, carrying its specific amino acid, pairs with the next codon. The ribosome holds two tRNA molecules at a time.
4. A peptide bond forms between the two amino acids in a condensation reaction, catalysed by the ribosome.
5. The ribosome moves along the mRNA by one codon. The first tRNA is released and can collect another amino acid from the cytoplasm.
6. A third tRNA pairs with the next codon, another peptide bond forms, and the process repeats.
7. When the ribosome reaches a stop codon (UAA, UAG or UGA), no tRNA matches it, and the completed polypeptide is released.Energy from ATP is needed to attach each amino acid to its tRNA.The polypeptide may then be modified and folded into its functional shape, for example in the rough endoplasmic reticulum and Golgi apparatus.Worked example: an mRNA has 101 codons including the start and stop codons. The start codon codes for methionine but the stop codon codes for nothing, so the polypeptide has 100 amino acids.
1. The mRNA binds to the small subunit of a ribosome, at the start codon AUG.2. A tRNA with the complementary anticodon (UAC) pairs with the start codon by hydrogen bonds, bringing methionine.
3. A second tRNA, carrying its specific amino acid, pairs with the next codon. The ribosome holds two tRNA molecules at a time.
4. A peptide bond forms between the two amino acids in a condensation reaction, catalysed by the ribosome.
5. The ribosome moves along the mRNA by one codon. The first tRNA is released and can collect another amino acid from the cytoplasm.
6. A third tRNA pairs with the next codon, another peptide bond forms, and the process repeats.
7. When the ribosome reaches a stop codon (UAA, UAG or UGA), no tRNA matches it, and the completed polypeptide is released.Energy from ATP is needed to attach each amino acid to its tRNA.The polypeptide may then be modified and folded into its functional shape, for example in the rough endoplasmic reticulum and Golgi apparatus.Worked example: an mRNA has 101 codons including the start and stop codons. The start codon codes for methionine but the stop codon codes for nothing, so the polypeptide has 100 amino acids.