Figure 40.1  Binding sites for transfer RNA. (A) Three tRNA molecules are shown in the tRNA-binding sites on the 70S ribosome. They are called the A (for aminoacyl), P (for peptidyl), and E (for exit) sites. Each tRNA molecule contacts both the 30S and the 50S subunit. (B) The tRNA molecules in sites A and P are base-paired with mRNA.