BIOLOGY Volume 1 - A Guide to General Biology - 2004

5. CELLS

5.7. Cell Fractionation

Cell/15.html">Microscopy has made an immense contribution to The Study of The Cell. However, investigating the Functions of individual Organelles requires a variety of other Research Methods as well. Typically, determining the function of a specific organelle involves isolating it from other cellular components and enabling it to carry out that function in vitro. To achieve this, Cells are disrupted (homogenized) by placing them in a suitable medium (with appropriate pH, ionic composition, and Temperature). This can be accomplished using a standard blender. The resulting mixture is then subjected to centrifugation. The higher the centrifugation speed, the smaller the particles that sediment (Fig. 5.9). Centrifugation is carried out in several steps with gradually increasing speeds. After each spin, the supernatant is separated from the pellet and subjected to further centrifugation. Each successive pellet contains progressively smaller organelles. This technique is known as differential centrifugation. Achieving high speeds requires a specialized centrifuge known as an ultracentrifuge.

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Fig. 5.9. Fractionation of cellular components using a centrifuge. Centrifugal acceleration generated by the centrifuge is measured in g-force (where g is the acceleration due to gravity).