A-site, P-site and E-site

A-site: the ribosomal site most frequently occupied by aminoacyl-tRNA. The aminoacyl-tRNA in the A-site functions as the acceptor for the growing protein during peptide bond formation.

P-site: the ribosomal site most frequently occupied by peptidyl-tRNA, i.e. the tRNA carrying the growing peptide chain. The P-site is also referred to as the puromycin sensitive site. Puromycin is an antibiotic which shows similarities with a part of aminoacyl-tRNA. When puromycin is present in the A-site, the peptide can be linked to puromycin via a peptide bond. Thus, peptidyl-tRNA in the P-site is located in the puromycin sensitive site.

E-site: the ribosomal site harbouring decylated tRNA on transit out from the ribosome.