Method of studying cells

Question 1

What is cell fractionation?

Answer 1

The process by which cells are broken up and the different organelles they contain are separated out

Question 2

What is centrifugation?

Answer 2

separating the organelles by spinning the solution at different and specific speeds

Question 3

Describe Stage 1 and why this has to happen

Answer 3

Fractionation cells are placed in a cold, buffered isotonic solution:

• cold to reduce enzyme activity that could damage the organelles
• buffered to maintain constant pH + prevent protein damage
• Isotonic to prevent cell organelles bursting/shrinking by osmosis

Question 4

Describe Stage 2

Answer 4

Homogenisation: cells are broken up by a homogeniser (blender) to release the organelles

Question 5

Describe Stage 3

Answer 5

The blended tissue is filtered through a sieve to remove insoluble material e.g cell walls, large pieces of unhomogenised tissue and connective tissue

Question 6

Describe Stage 4

Answer 6

Ultracentrifugation:

• The filtrate is placed in a centrifuge and span at slow speed
• The heaviest organelles (e.g nuclei) are forced to the bottom + form a thin pellet
• The fluid a the top (supernatant) is removed
• The supernatant can be re-spun at a faster speed to gain the next heaviest organelles (e.g chloroplasts)

Question 7

What is left?

Answer 7

After centrifuging all the cell organelles (separately) it leaves the cytoplasm