It is impossible to study the functions of the organelles of a cell without disrupting the cell that contains them. Cell fractionation is the process of separating the various living components of the cell while maintaining their individual functions.

The same way a tissue can be fractionated into its living constituent cell types, cells can be broken down into the organelles they contain, along with the isolation, purification, and analysis of proteins and other large molecules in the cytosol.

Modern biologists also use cell fractionation to create an enriched source of proteins of interest for further purification, and in the diagnosis of disease.
A dictionary definition of cell fractionation to share with your students”
Cell fractionation is a set of procedures for rupturing cells so their constituents can be separated and suspended in an isotonic medium, so modern biologists can study the structure, chemical composition, and function of constituent organelles.

Make sure your students understand the significance of suspending organelles in an isotonic medium.

What are the Steps to Cell Fractionation?

Any method of cell fractionation will involve extraction, homogenization, and, finally, centrifugation.

The first step of cell fractionation is liberating the cells from the tissues that contain them. This step must be mild enough that it does not damage the organelles or denature the proteins targeted for study or purification.
In many cases, this step can be accomplished with a first round of centrifugation

Centrifugal force disrupts connective tissue and adhesion molecules to free individual cells. Then the mixture of whole cells can be suspended in an isotonic solution, usually saline or a mixture of sugar and water, at a biological temperature.

In studies of cell components of animal origin, this solution might be maintained at a temperature of about 40°C. The solution must be isotonic to the content of the cells so they will neither rupture as they fill with fluid nor leak cations and proteins into the suspension medium.

The next step in cell fractionation is the liberation of organelles from within the individual cells. This can be done by:

  • Grinding. Even a mortar and pestle can be used to create a crude mixture of cells and cell organelles.
  • Osmotic shock. In this method, individual cells are placed in a hypotonic solution so they absorb water and their walls or membranes rupture.
  • High pressure, a French press or nitrogen bomb, or
  • Sonification. In this method, cells are placed in a high-speed blender that applies force not with blades but with two cylinders separated by a tiny air gap.

The results of this step are transferred with a steel rod to a higher-speed, lower-temperature centrifuge that separates cell constituents by weight. Individual proteins will form their own band in this process.

The Best Uses for Cell Fractionation

What is the most obvious use of cell fractionation for an advanced high school or college biology class? Isolating DNA!

In Modern Biology’s Experiment B1-2: Cell Fractionation and DNA Isolation, your students will first isolate nuclei from calf thymus tissue. After they examine them under the microscope, they will extract DNA with a simple procedure that contains nothing more than detergent and alcohol. A small centrifuge is helpful but not essential to the exercise.

Every Modern Biology kit includes all the reagents and test materials teachers need for their laboratory exercise. There’s no ordering separate reagents, fussing about missing shipments, or checking out lab materials from the supply room.

Modern Biology supplies the safe, non-toxic, reliable reagents and measurement materials you need for every laboratory exercise. And because Modern Biology saves you the hassle and expense of ordering reagents separately, it is a lot easier to stay within your budget for the class.

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