Cell Fractionation

Question 1

What is cell fractionation?

Answer 1

Cell fractionation is the process by which cells are broken up and their organelles separated.

Question 2

What happens to the cell before fractionation?

Answer 2

Before fractionation the cells are placed in a cold, buffered and isotonic solution. It is cold to reduce enzyme activity, buffered to maintain a constant pH and isotonic to prevent cells from bursting.

Question 3

What are the two stages to cell fractionation?

Answer 3

Homogenisation and ultracentrifugation.

Question 4

What is homogenisation?

Answer 4

Cells are broken up by a homogeniser to release the organelles. Any cells still intact are filtered out to the leave the homogenate.

Question 5

What is ultracentrifugation?

Answer 5

The homogenate is placed in an ultracentrifuge and spun at a slow speed initially, the heaviest organelles are forced to the bottom and form a thin pellet. The fluid at the top, the supernatant, is removed. The supernatant can then be respun at a faster speed to gain the next heaviest organelle. The process is repeated.

Question 6

What order do the pellets form in?

Answer 6

1. (1000) Nuclei (10 mins)
2. (3500) Mitochondria and Chloroplasts (10 mins)
3. (16500) Lysosomes and Endoplasmic Reticulum (20 mins)
4. (100000) Ribosomes (60 mins)