University:
Liberty University
Course:
BIOM 500 | Introduction to Biomedical Sciences
Academic year:

2024
Views:

385

Pages:

5
Author:

Sheha A.

Stage Initiation of Protein Synthesis Activation of amino acid: During the process of protein synthesis, aminoacyl tRNA synthetases esterify the 20 amino acids to corresponding tRNAs. A Specific amino acid initiates protein synthesis: Protein synthesis begins at amino terminal and proceeds by stepwise addition of amino acids to the carboxyl terminal end of the polypeptide chain. Initiation codon: The codon that specifies methionine residue is the initiation codon for protein synthesis. In prokaryotes, the initiation codon is N-formyl methionine. 3. Initiation: Initiation requires 30S ribosomal subunit, mRNA coding for the polypeptide to be made, the initiator tRNA-fMet, a set of three proteins called initiation factor (IF1, IF2, IF3), GTP, and 50S subunit. This is the first step of initiation. 30S ribosomal subunit binds to initiation factors IF1, IF2, IF3, and mRNA, preventing 30S and 50S subunits from combining prematurely. The mRNA then binds to the 30S subunit. In the second step of initiation process, the complex consisting of 30S ribosomal subunit, tRNA-fMet, and mRNA is joined by GTP-bound IF-2 and the 50S ribosomal subunit. In third step of initiation: This large complex combines with 50S ribosomal subunit. Simultaneously, the GTP bound to IF-2 is hydrolyzed to GDP + Pi which are released from complex. All the three initiation factors depart from ribosome at this point. This step produces a functional 70S ribosome called initiation complex containing mRNA and the initiating tRNA-fMet.