UNIT 2 (topic 1) cell fractionation

Question 1

why do you prepare in cold solution

Answer 1

lysosomes activity decreases so don’t release digestive enzymes that will digest organelles

Question 2

why do you prepare in an isotonic solution

Answer 2

chemistry of the cytoplasm is delicately balanced - water potential could become unbalanced

Question 3

why do you prepare in a buffered solution

Answer 3

pH remains constant so protein organelles don’t denature (tertiary structure)

Question 4

what are the stages of cell fractionation

Answer 4

• homogenation
• ultracentrifugation

Question 5

explain homogenation

Answer 5

tissue is placed in the homogeniser
- breaks open the cell membrane releasing the organelles
- then filtered to get rid of any unbroken cells and large pieces of debris

Question 6

explain ultracentrifugation

Answer 6

filtered homogenate is put in a centrifuge
- spins the homogenate at varying speeds
- heaviest, most dense organelles go to the bottom first
- supernatant is removed from pellet
- spun faster to get the next heaviest organelle to the bottom

Question 7

define pellet

Answer 7

organelles that are at the bottom of the homogenate

Question 8

what is the order of organelles, most dense to least dense

Answer 8

nuclei, chloroplasts, mitochondria, lysosomes, ribosomes