Preparing the cell contents
Cell fractionation separates cell components so that particular organelles can be isolated for closer study.
The first stage is homogenisation. Cells are broken open using a homogeniser, disrupting the cell-surface membranes and releasing the organelles into a liquid called the homogenate.
Conditions during homogenisation
The tissue is homogenised in a solution that is cold, isotonic and buffered.
| Condition | Why it is needed |
|---|---|
| Cold | Slows enzyme activity, reducing the breakdown of organelles. |
| Isotonic | Prevents organelles being damaged by osmotic movement of water. |
| Buffered | Maintains a stable pH, helping to prevent proteins and enzymes from being denatured. |
Filtration
The homogenate is passed through gauze. Large pieces of tissue and other cell debris are retained, while the organelles pass through in the liquid filtrate.
- Place the tissue or cell sample in a cold, isotonic, buffered solution.
- Use a homogeniser to break the cells open.
- Collect the resulting homogenate.
- Filter the homogenate through gauze to remove large debris.
- Collect the filtrate, which contains a mixture of organelles.
Exam Tip: If asked why the homogenising solution is cold, isotonic and buffered, give a separate biological reason for each condition rather than treating them as one point.