Site pages
Current course
Participants
General
18 February - 24 February
25 February - 3 March
4 March - 10 March
11 March - 17 March
18 March - 24 March
25 March - 31 March
1 April - 7 April
8 April - 14 April
15 April - 21 April
22 April - 28 April
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. |