Question

Two ribosomal subunits have sedimentation coefficients of 60S and 40S. Assuming that both subunits have spherical shapes and their densities are equal, calculate the ratio of their molecular weights ( not with the actual molecular weight values).

Answer 1

The sedimentation coefficients are 60 S & 40 S

both subunits have spherical shapes & their densities are equal

1 Swedberg unit= 10^-13

Two ribosomal subunits have Sedimentation coefficient =

Large subunit= 60 S

= 60 X 10^-13

small subunit = 40S

   = 40 X 10^-13

molecular mass of 60 S subunit is = 3 million gram /mole

& 40S subunit = 1.5 million gm /mole

ratio of their molecular weight = large subunit / small subunit

   = 3 /1.5

   = 1.5 million gram /mole