Defenition: the process used to separate cellular components while preserving their individual functions.

Process:

1. Cut up sample into pieces and immerse in a cold, isotonic, buffered solution.

2. Blend the sample until it is homogenised.

3. Place in an ultracentrifuge and spin at a high speed for 10 minutes

4. separate the sediment (thicker sludge at the bottom) from the supernatant (the suspension of the other organelles in solution)

5. Put the supernatant into the ultracentrifuge and repeat the process until you have separated the intended organelle from the solution.

Why does this work?

As the ultracentrifuge spins, centripetal force pushes the organelles with the most mass to the bottom of the container. This allows the organelles to separate by their masses.

The Solution

Must be:

1. Cold - this is to reduce enzyme activity. Once the sample is homogenised (fully blended), the cell membranes of some organelles may be ruptured. For example, lysosomes contain digestive enzymes which may leak into the solution. The rate of reaction of enzyme activity is decreased in cold environments.

2. Isotonic - this means that the solution contains the correct levels of dissolved salts and sugars. This means that water will not travel into or out of organelles by osmosis, which prevents the organelles from shrivelling up or bursting.

3. Buffered - organelles may die or function inefficiently in certain pH values. A buffer regulates the pH of the solution. This pH value can be changed if necessary.