Bke2 Biochemistry Lectures

Lecture 33: Protein synthesis
Reading material: Horton, Chapter 23 in 2nd Ed; 22 in 3rd Ed (Stryer, Chapter 34)

Abstract: Amino acids are activated and linked to particular tRNA molecules by specific aminoacyl tRNA synthetases. Protein synthesis takes place on ribosomes, which are composed of rRNA (2/3) and many proteins. The ribosome contains three binding sites for tRNA, the A (aminoacyl) P (peptidyl) and E (exit) sites. The aminoacyl tRNA is delivered to the A site of the ribosome by the GTP form of elongation factor Tu. A peptide bond is made to the peptide attached to the tRNA in the P site by peptidyltransferase. This is formed by the 23S rRNA. The peptide then sits at the tRNA in the A site. In the translocation step the tRNA molecules and the mRNA are moved so that the free tRNA at the P site moves to the E site and the tRNA with the peptide in the A site moves to the P site. Then another cycle in the peptide synthesis can take place.

Peptide synthesis is initiated in prokaryotes by the binding of formylmehionyl-tRNA to the P site of the ribosome. In eukaryotes, methionine bound to a special tRNA participates in the initiation. Protein synthesis is terminated by the binding of release factors to stop codons of the mRNA.

Key concepts:
Translation
tRNA
Codon/anticodon
Aminoacyl tRNA synthetases
Ribosome
30S, 50S subunits
rRNA, proteins
A (aminoacyl) P (peptidyl) and E (exit) sites
Elongation factor Tu
Peptidyltransferase
Translocation
Initiation
Termination