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Alberts B, Bray D, Lewis J, et al. Molecular Biology of the Cell. 3rd edition. New York: Garland Science; 1994.

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Cover of Molecular Biology of the Cell

Molecular Biology of the Cell. 3rd edition.

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Figure 4-36. Comparison of methods of velocity sedimentation and equilibrium sedimentation.

Figure 4-36Comparison of methods of velocity sedimentation and equilibrium sedimentation

In velocity sedimentation (A) subcellular components sediment at different speeds according to their size when layered over a dilute sucrose-containing solution. In order to stabilize the sedimenting bands against convective mixing caused by small differences in temperature or solute concentration, the tube contains a continuous shallow gradient of sucrose that increases in concentration toward the bottom of the tube (typically from 5% to 20% sucrose). Following centrifugation, the different components can be collected individually, most simply by puncturing the plastic centrifuge tube and collecting drops from the bottom, as illustrated here. In equilibrium sedimentation (B) subcellular components may move up or down when centrifuged in a gradient until they reach a position where their density matches their surroundings. Although a sucrose gradient is shown here, denser gradients, which are especially useful for protein and nucleic acid separation, can be formed from cesium chloride. The final bands, at equilibrium, can be collected as in (A).

From: Fractionation of Cells and Analysis of Their Molecules

Copyright © 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D Watson.

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