Practice question

Sedimentation coefficient S measured in Svedberg units quantifies particle velocity in ultracentrifuge under standard conditions. It does not directly equal molecular weight because hydrodynamic friction matters. S depends on molecular mass, partial specific volume, solvent density, and shape expressed via frictional coefficient. Compact spherical particles sediment faster than elongated rods of same mass due to lower drag. Hence mitochondrial 55S being more massive than bacterial 70S yet sedimenting slower illustrates shape and density effects, as proteins increase porosity and lower sedimentation despite higher mass.