5.12.1 Mechanism of Translation · Part 4

and mRNA. Neomycin inhibits the interaction between tRNA and mRNA. Erythromycin inhibits the translocation of mRNA along the ribosome. Streptomycin inhibits the initiation of translation and causes misreading. Chloramphenicol inhibits peptidyl transferase and formation of peptide bonds. Structure of the operon : Each operon is a unit of gene expression and regulation and consists of one or more structural genes and an adjacent operator gene that controls transcriptional activity of the structural gene. i) The structural gene codes for proteins, rRNA and tRNA required by the cell. ii) Promoters are the signal sequences in DNA that initiate RNA synthesis. RNA polymerase binds to the promoter prior to the initiation of transcription. step ). An additional amino acid is added to the growing polypeptide, each time mRNA advances through the ribosome. Once a polypeptide chain is assembled, it emerges out from the base of the large subunit ( Fig. . c ). Termination is the final phase of translation. Termination of protein synthesis occurs when one of the three stop codons appears in the ‘A’ site of the ribosome. The terminal codon signals the action of GTP – dependent release factor, which cleaves the polypeptide chain from the terminal tRNA releasing it from the translational complex (step ). The tRNA is then released from the ribosome, which then dissociates into its subunits (step ) ( Fig. . d ). Fig. . d- Termination of the process of translation