cell centrifugation

Question 1

) In the first step in this procedure, the leaves were homogenised by grinding in cold buffer solution. Explain why

(ii) a buffer solution was used.

Answer 1

keep pH the same / controls pH;
prevent change to / denaturing of proteins / enzymes;

Question 2

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells.

Answer 2

ell homogenisation to break open cells;

1. Accept suitable method of breaking open cells.
2. Filter to remove (large) debris / whole cells;
3. Reject removes cell walls.
4. Use isotonic solution to prevent damage to mitochondria / organelles;
5. Ignore to prevent damage to cells.
6. Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation;
7. Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments / heavy organelles;
8. Ignore incorrect numerical values.
9. Re-spin (supernatant / after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom.
10. Must have location

Question 3

Small samples of plant tissue were placed in a cold, isotonic solution and then treated to break open the cells to release the organelles. The different organelles were then separated. Describe a technique that could be used to

(i) break open the cells;

Answer 3

homogeniser / blender / pestle and mortar / description
e.g. grind with sand;