Food Chemistry and Fish in Nutrition ( 2+1)

8.3.1.3. Termination

In comparison to initiation and elongation, termination is a relatively simple process. After multiple cycles of elongation culminating in polymerization of the specific amino acids into a protein molecule, the nonsence or terminating codon of mRNA (UUA, UAG, UGA) appears in the a site. Normally, there is no tRNA with an initiation codon capable of recognizing such a termination signal. Releasing factors (eRF) are capable of recognizing that a termination single resides in the A site. The releasing factor, in conjunction with GTP and the peptidyl transferase, promotes the hydrolysis of the bond between the peptide and the tRNA occupying the P Site.

Thus, a water molecule, rather than an amino acid, is added. This hydrolysis releases the protein and the tRNA from the P site. Upon hydrolysis and release, the 80S ribosome dissociates into its 40S and 60S subunits, which are then recycled. Therefore, the leasing factors are proteins that hydrolyze the peptidyl-tRNA bond when a nonsense codon occupies the A site.

The mRNA is then released from the ribosome, which dissociates into its component 40S and 60S subunits, and another cycle can be repeated.
In animal cells, many proteins are synthesised from the mRNA template as a precursor molecule which is then modified to form the required active protein.