iGen 06-14

Eukaryotic ribosome rRNA / tRNA / mRNA complex

    Ribosomes comprise a Small Subunit (SSU) and a Large Subunit (LSU) that includes rRNA molecules. Each subunit contributes to an Exit ("E"), Peptidyl ("P") site, and an Aminoacyl ("A") site. During translation, tRNA molecules enter the right-hand A site, pass to the middle P site, and are released from the left-hand E site. To ensure that the mRNA will be read 5'3', it is convenient to think of the ribosomal complex as moving along a fixed mRNA molecule in the 5'3' direction. Note however that this motion is relative: one can also think of the ribosome as fixed, and the mRNA molecule, starting with the 5' end.

   IMPORTANT: The EPA sites may be drawn left to right, or right to left, and the LSU and SSU above or below each other: remember that "top / bottom" & "left / right" are arbitrary conventions to make 5'3' rRNA transactions easier to describe.


Figure © 2010 PJ Russell, iGenetics 3rd ed.; all text material © 2014 by Steven M. Carr