tRNA, the A-, P-, and E-sites (short for aminoacyl-tRNA, peptidyl-tRNA, and exit, respectively). (A) This representation of a ribosome, which will be used in subsequent figures, is highly schematic. (B) A model of the prokaryote ribosome that depicts the arrangement of the mRNA (orange beads) and the positions of one tRNA molecule in the A-site of the ribosome (pink), one tRNA molecule in the P-site of the ribosome (green), and one tRNA molecule in the E-site of the ribosome (yellow). In this model the large ribosomal subunit is light blue, and the small subunit is light green. Although all three tRNA sites are shown occupied here, during the process of protein synthesis not more than two of these sites contain tRNA molecules at any one time.
