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

2024
Views:

46

Pages:

9
Author:

Sheha A.

Stage Initiation of Protein Synthesis Activation of Amino Acids: Begins the process of protein synthesis. Aminoacyl-tRNA synthetases attach the 20 amino acids to corresponding tRNAs. Initiation: A specific amino acid initiates protein synthesis. Protein synthesis begins at the 5' end of mRNA and proceeds by adding amino acids to the carboxyl terminal end of the polypeptide chain. The mRNA codon that specifies methionine serves as the initiation codon. In prokaryotes, the initiation codon is N-formyl methionine. 3. Initiation: Initiation is the first step of polypeptide synthesis. Proteins initiate with Met-tRNA as the start codon. Proteins, GTP, 50S subunit, mRNA, and initiation factors (IF1, IF2, IF3) combine. In the first step of initiation: 30S subunit, IF1, IF2, IF3, GTP, and mRNA combine. 50S subunit combines with the initiation complex. In the second step of initiation: The initiation complex consisting of 30S subunit, IF1, IF2, IF3, GTP, mRNA, and fMet-tRNA is joined by the 50S subunit. GTP is hydrolyzed to GDP and Pi. IF1 and IF2 are released. In the third step of initiation: All initiation factors are released. The 50S subunit binds to the initiation complex. GTP is hydrolyzed to GDP and Pi. The initiation codon is positioned correctly in the P site. Step 4: A complex of GTP-bound EF-Tu-tRNA binds to complex comprising 50S-mRNA-fMet-tRNA. GTP is hydrolyzed and EF-Tu-GDP complex is released. The EF-Tu-GDP complex is recycled in a process involving EF-Ts and GTP. Step 5: A peptide bond is formed by condensation reaction between the amino acid bound to tRNA in the A site and the amino acid bound to tRNA in the P site on the ribosome. This occurs by transfer of N-formylmethionine group from tRNA in the P site to amino acid in the A site. Now in A site is a dipeptide tRNA bound to the P site. The uncharged tRNA is released from the P site. This association of peptide bond formation is catalyzed by peptidyl transferase. Step 6: Translocation takes place. The ribosome moves one codon along the mRNA. The dipeptide tRNA is now in the P site, and the A site is empty.