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Sedimentation (24.7)

Sedimentation (24.7). When macromolecules move in solution, their motion is dictated by the forces they feel Gravitational force (F g ) is opposed by frictional (F fr ) and buoyant (F b ) forces

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Sedimentation (24.7)

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  1. Sedimentation (24.7) • When macromolecules move in solution, their motion is dictated by the forces they feel • Gravitational force (Fg) is opposed by frictional (Ffr) and buoyant (Fb) forces • Specific volume of the solute is the change in solution volume upon addition of a given amount of solvent (measure in cm3/g) • When all forces sum to zero, terminal velocity is achieved (vter) • Sedimentation coefficient relates speed of sedimentation to properties of macromolecule and solvent • Measured in units of Svedbergs (S) where 1S = 1 x 10-13 s

  2. Velocity Sedimentation (24.7) • Velocity sedimentation utilizes centripetal force instead of gravity • ω is the angular velocity (i.e., speed of centrifuge) and x is the distance between the particle and the center of rotation • Centrifugation causes heavier particles (solute) to move away from center of rotation • Boundary forms with one side being solution and the other side solvent • Sedimentation coefficient can be determined by monitoring motion of boundary • Sedimentation coefficients can give us molar mass (M = mNA) of the macromolecule if we know the frictional coefficient • We can get this from a diffusion experiment

  3. Sedimentation Forces

  4. Centrifuge Cell for Velocity Sedimentation

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