Cell Fractionation (subsection of 3.1)

Question 1

What does ‘homogenise’ mean?

Answer 1

To break up the tissue and break open the cells.

Question 2

What is a ‘homogeniser’?

Answer 2

A glass tube that contains a plunger.

Question 3

What does steps must take place before cell fractionation can occur?

Answer 3

The tissue is cut up and kept in a cold, isotonic, buffered solution.

Question 4

What is the effect of the ‘buffer solution’?

Answer 4

To keep the pH constant/ It prevents the pH from fluctuating

Question 5

What effect does the pH changing have on the cells?

Answer 5

The enzymes in the cell’s organelles could denature

Question 6

What effect does the water potential of the buffer have on the cells?

Answer 6

It prevents water from moving into organelles by osmosis and causing them to burst

Question 7

What effect does keeping the sample cold have on the cells?

Answer 7

It reduces enzyme activity

Question 8

What is the cell homogenate?

Answer 8

It’s a fluid that contains all the organelles that we find in the cell.

Question 9

What is the order of largest to smallest organelles in cells?

1. _________
2. _________
3. _________
4. _________

Answer 9

1. Nucleus
2. Mitochondria
3. Lysosomes
4. Ribosomes

Question 10

What is cell fractionation?

Answer 10

It is the process by which different organelles in a cell are separated out

Question 11

What are the two stages to cell fractionation?

Answer 11

1. Homogenisation
2. Ultracentrifugation

Question 12

What is meant by the term centrifuge?

Answer 12

A machine that spins the homogenate at very high speeds

Question 13

What is meant by ultracentrifugation?

Answer 13

The process by which the fragments in the filtered homgenate are seperated in a centrifuge.

Question 14

What does steps take place in the process of ultracentriguation?

Answer 14

1. The tube of filtrate is placed in the centrifuge and spun at a slow speed
2. The heaviest organelles (nuclei) are forced at the bottom of the tube where they form a thin sediment or pellet
3. The fluid at the top of the tube (supernatant) is removed, leaving just the sediment of nuclei.
4. The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before
5. The next heaviest organelles (mitochondria) are forced at the bottom
6. The process is continued this way , so that at each increase in speed, the next heaviest organelle is sedimented and separated out