Ribosome Stage
Progress
Codon
—
Position
0 / —
Amino Acids
0
A-site
empty
Controls
Key Sites
A site — Aminoacyl: incoming charged tRNA binds here.
P site — Peptidyl: holds tRNA carrying the growing chain.
E site — Exit: empty tRNA leaves through here.
P site — Peptidyl: holds tRNA carrying the growing chain.
E site — Exit: empty tRNA leaves through here.
Why 80S, not 100S?
This is a eukaryotic ribosome. The 40S and 60S subunits combine to form an 80S ribosome — not 100S.
S = Svedberg unit, a measure of sedimentation rate (not mass). It is non-additive: when subunits join, the assembled particle's shape changes how it sediments, so 40S + 60S = 80S, not 100S.
S = Svedberg unit, a measure of sedimentation rate (not mass). It is non-additive: when subunits join, the assembled particle's shape changes how it sediments, so 40S + 60S = 80S, not 100S.