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" & "left" are arbitrary conventions to make 5'
3' rRNA transactions
easier to describe.
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" & "left" are arbitrary conventions to make 5'
3' rRNA transactions
easier to describe.