Cells (FRACTIONATION & ULTRACENTRIFUGATION)

Question 1

What is cell fractionation

Answer 1

Cell fractionation is the process in which different parts and organelles of a cell a separated so that they can be studied in detail. The most common method of cell fractionation is differential centrifugation.

Question 2

Give the 3 steps for cell centrifugation

Answer 2

1) Homogenisation
2) Filtration
3) Ultracentrifugation

Question 3

Describe stage 1 of cell differential centrifugation

Answer 3

Homogenisation
Cells are broken up by grinding them in a blender
–> Solution must be ice cold to reduce enzyme activity
–> Solution must be isotonic to prevent damage of organelles through osmosis
–> Solution must be buffered to stop enzymes from denaturing

Question 4

Describe stage 2 of cell centrifugation

Answer 4

Filtration
–> Homogenised cell solution (homogenate) is filtered to seperate cell debris from organelles

Question 5

Describe stage 3 of cell centrifugation

Answer 5

Ultracentrifugation
–> Cell fragments are spun in centrifuge at low speed. Heaviest organelles (eg: nuclei) form pellent at bottom of tube
–> The fluid at the top, called the supernatant, is removed which leaves just the sediment of
the nuclei. The supernatant is then transferred to another tube and spun at a slightly faster speed. This time the pellet that forms contains the next heaviest organelle, the mitochondria.
– This process continues so that each time the speed is increased the next heaviest organelle is sedimented and separated out.