The ribosome is the site of which translation occurs. Ribosomes have a large and small subunit, each constructed from ribosome RNA (rRNA) and protein. Protein synthesis happens as a result of collaboration between tRNA, mRNA and the ribosome. The tRNA traverse along three sites of the ribosome in the order: A, P, and E.

  • The A (amino acid) site is where the tRNA, with attached amino acid, bind to the mRNA codon
  • The site where the tRNA adds its amino acid to the polypeptide chain is the P (polypeptide) site
  • The E (exit) site is where tRNA resides before being releasesed from the ribosome

On the right, a large globular 3 dimensional shape shows three chemical structures inside labelled from left to right, E P and A. A cartoon of this structure is shown on the right with three compartments inside labelled E P and A. A cartoon strand of mRNA with 5 prime at the left and 3 prime at the right is shown as a long thin string with letters attached to it. It is held inside the ribosome with three letters in each compartment. The top portion of both images is labelled small subunit and the bottom portion of the ribosome is labelled large subunit. The mRNA binding site is indicated within the small subunit and located between P and A.

Figure 1. The Ribosome