Microbiology Procedure

Index >> Protein Synthesis >> Peptide Bond Formation

Peptide Bond Formation

	Peptide Bond Formation - The starting amino acid (N-formylmethionine in prokaryotes and methionine in eukaryotes) is now united by a peptide bond with the second amino acid (aa₂). The tRNA molecule of fMet tRNA or Met tRNA is discharged from the P site, and the unloaded molecule is cast off from the ribosome. The second amino acid (aa₂) remains attached to its tRNA through its carboxyl group. Attached to it is methionine/N-formylmethionine by means of the peptide bond. Peptide bond formation docs not require any external source of energy or soluble factors. It is catalysed by the peptidyl transferase complex located in the large subunit. The enzyme peptidyl transferase is probably composed of the A site the P site and a catalytic centre. Its activity may, however, be influenced by several neighboring proteins. The A site is located near proteins L6, L15, LI6 and L18 and the P site in the vicinity of L2, L11, L18, L20 and L27.
The newly formed polypeptide chain travels through a peptide groove consisting of binary and ternary complexes the following scheme may be L2, L20, L24, L27 and L32-33. The protein L11 was proposed as the catalytic centre of peptidyl transferase, although later reports have cast some doubts on this. 238 rRNA probably has a structural or functional role in peptidyl transferase. There is evidence that this RNA is present in the peptide groove. It has been suggested that there is complementary binding between the -C-C-A ends of aminoacyl tRNA and peptidyl tRNA with UGG sequences of 238 tRNA at the A and P sites of peptidyl transferase.
The tRNA molecule to which the growing polypeptide chain is attached is called peptidyl tRNA. It is bound to the P site (peptidyl donor site). The incoming tRNA molecule bearing an amino acid molecule is called aminoacyl tRNA. It binds to the A site (acceptor site). During the formation of the peptide bond there is a transfer of the polypeptide chain from peptidyl tRNA to aminoacyl tRNA. The carboxyl ester link of peptidyl tRNA is broken and a new peptide bond is formed with the amino acid of aminoacyl tRNA. The peptide bond is a covalent bond between two amino acid molecules. The α amino group of one amino acid is bonded to the α carboxyl group of the other. During this process there is elimination of H₂O.

	Back to Home
Protein Synthesis Part 1 Release of Deacylated tRNA Hydrolysis of GTP Locking and Unlocking Ribosome Model inchworn Theory Conformational Changes Recognition of the Termination Signal Release of the Polypeptide Chain Prokaryote and Eukaryote Release Factors Processing Polypeptide Chain Rate of Protein Synthesis Signal Hypothesis Prokaryote and Eukaryote Protein Synthesis Teminism

Home | Site map | Submit Article | Resources | Search

Language >> English | Français | Español | Deutsch | Italiano | Portugues | Japanese | Korean | Sim-Chinese