3.1 Cell structure (ultracentrifugation)

Question 1

What is cell fractionation

Answer 1

The process where cells are broken up an the different organelles they contain are separated

Question 2

What is the tissue places in before cell fractionation occurs

Answer 2

In a cold, buffered solution of the same water potential (isotonic)

Question 3

State the use of the components of the solution

Answer 3

Cold: reduces enzyme activity that might break down the organelles
Isotonic: Prevents organelles from bursting or shrinking as a result of osmotic gain or loss of water
Buffered: So the pH does not fluctuate

Question 4

What are the two stages of cell fractionation

Answer 4

Homogenation
Ultracentrifugation

Question 5

What happens in homogenation

Answer 5

Cells are broken up up by a homogeniser
This releases the organelles from the cell
The homogenate is filtered to remove any complete cells and large pieces of debris

Question 6

What happens in ultracentrifugation

Answer 6

The fragments in the filtered homogenate are separated in a centrifuge
Centrifuge: spins tubes of homogenate at very high speeds in order to create a centrifugal force

Question 7

What is the process of cell fractionation for animal cells

Answer 7

• Tube of filtrate spun at low speed in the centrifuge
• Heaviest organelles are forced to the bottom of the tube. A pellet is formed.
• The supernatant is removed; sediment of nuclei is left behind.
• Supernatant is transferred to another tube & spun at a faster speed in the centrifuge
• Next heaviest organelles, mitochondria, are forced to the bottom of the tube.
• Process is continued, so the next heaviest organelle is sedimented & separated out.