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AAT Bioquest

Why do 60S & 40S ribosomal subunits make an 80S ribosome instead of the 100S?

Posted December 13, 2022


Answer

The 80S ribosome is identified according to its sedimentation coefficients in Svedberg units.  Since it is a measure of sedimentation time, it is not simply a sum of subunits. Svedberg units are a nonlinear function, and 60S and 40S are two separate subunits that together sediment at 80S. If it were a matter of size or mass, they could be added up to 100S, but the Svedberg unit is a measure of time based on speed instead.  

Additional resources

Theordore Svedberg and the Ultracentrifuge

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