VPB 321: Animal Biotechnology (2+1)

INITIATION

• The purpose of initaition step is to assemble a complete ribosome on to an mRNA molecule at the start point, the initiation codon.
• The components involved are the large and small subunits, the mRNA, the initiator tRNA in its charged form, the three initiation factors (IF1, IF2 and IF3) and GTP.
• IF1 and IF2 bind to a free 30S subunit. This helps to prevent a large subunit binding to it without an mRNA molecule and forming an inactive ribosome.
• IF3 complexed with GTP then binds to the small subunit . It will assist the charged initiator tRNA to bind.
• The assembled ribosome has two tRNA binding sites. These are called A-site or acceptor) for aminoacyl and P-site (or donor) and peptidyl sites. The A-site is where incoming aminoacyl - tRNA molecules bind and the P-site where the growing polypeptide chain is usually found.
• One major outcome of initiation is the placement of the initiator tRNA in the P-site.