Translation is the second part of the central dogma of molecular biology : RNA → Protein. It is the process in which the genetic code in mRNA is read to make a protein on a ribosome. After mRNA leaves the nucleus, it moves to a ribosome, which consists of rRNA and proteins. The ribosome reads the sequence of codons in mRNA. Molecules of tRNA bring amino acids to the ribosome in the correct sequence. Amino acids thus brought are joined with peptide bonds, at the expense of energy, forming long chain – Proteins.
Aminoacylation of tRNA or Charging of tRNA happens when amino acids are linked to their cognate tRNA in the presence of ATP.
- mRNA joins with the small subunit of ribosome to form initiation complex & translation begins. This is followed by activation of ribosome when both, large & small, subunit join each other.
- Initiation of polypeptide chain –The initiator t RNA recognizes the start codon (AUG) and helps ribosome to bind to it, there are two sites on the large subunit for two amino acids to bind which are so close to each other that a peptide bond is formed between them.
- During the elongation stage, “tRNA – amino acid complexes”, sequentially bind to the codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into Polypeptide sequences dictated by DNA and represented by mRNA.
- The translational unit in mRNA is flanked by the start codon (AUG) & a stop codon ( UAA / UAG / UGA) & codes for a polypeptide. The untranslated regions (UTRs), present at both 5’ end (before start codon ) and 3’ end (after stop codon),on the mRNA are needed for efficient translation. A release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.