Initiation
The first stage of translation involves the assembly of the three components that carry out the process (mRNA, tRNA, ribosome)
The small ribosomal subunit binds to the 5’-end of the mRNA and moves along it until it reaches the start codon (AUG)
Next, the appropriate tRNA molecule bind to the codon via its anticodon (according to complementary base pairing)
Finally, the large ribosomal subunit aligns itself to the tRNA molecule at the P site and forms a complex with the small subunit
Understanding:
Synthesis of the polypeptide involves a repeated cycle of events
Elongation
A second tRNA molecule pairs with the next codon in the ribosomal A site
The amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site
The tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site carries the peptide chain
Translocation
The ribosome moves along the mRNA strand by one codon position (in a 5’ → 3’ direction)
The deacylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site
Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated
Understanding:
Disassembly of the components follows termination of translation
Termination
The final stage of translation involves the disassembly of the components and the release of a polypeptide chain
Elongation and translocation continue in a repeating cycle until the ribosome reaches a stop codon
These codons do not recruit a tRNA molecule, but instead recruit a release factor that signals for translation to stop
The polypeptide is released and the ribosome disassembles back into its two independent subunits