Lesson 5: Organelles and Compartmentalisation

Question 1

What structures are not considered organelles?

Answer 1

cell wall
cytoplasm
cytoskeleton

Question 2

What is the purpose of cell fractionation?

Answer 2

Isolate different organelles.

Question 3

what are the two main steps to cell fractionation?

Answer 3

homogenisation and ultracentrifugation.

Question 4

What are the steps of homogenisation?

Answer 4

1. Tissues containing cells is broken up in a blender. The cells are blended in a cold, buffered and isotonic solution.
2. Blended solution is filtered to remove large cell debris.

Question 5

why does the tissue need to be blended in a cold, buffered and iostonic solution?

Answer 5

Cold: reduces enzyme activity which could damage ther organelles.
Isotonic: prevent bursting or shrivelling of cells.
Buffered: maintains the pH to prevent proteins denaturing.

Question 6

what are the steps to ultracentrifugation?

Answer 6

1. filtered solution is spun at a low speed by an ultracentrifuge.
2. The densest organelles form a pellet at the bottom of the centrifuge tube.
3. Pellet is removed, process is repeated at higher speeds, producing a series of pellets containing one type of organelle each time.

Question 7

What is phagocytosis?

Answer 7

process which solid material such as bacteria is taken into a cell by endocytosis.

Question 8

What are the steps of Phagocytosis?

Answer 8

1. A bacterium is taken into a cell by endocytosis, forming a phagocytic vacuole.
2. Lysosomes fuse with the phagocytic vacuole to form a phagosome.
3. The lysosome’s enzymes digest the bacterium.
4. soluble debris is excreted by exocytosis.

Question 9

Why should the nucleus be compartmentalised?

Answer 9

protection of DNA from harmful reactions in the cytoplasm.
maintains ideal conditions for transcription
allows the nucleus to break down into vesicles during mitosis and meiosis.

Question 10

What are vesicles?

Answer 10

membrane-bound sacs used for transport and storage

Question 11

What is the role of clathrins?

Answer 11

proteins that help with the formation of vesicles

Question 12

How are clathrin-coated vesicles formed?

Answer 12

1. Clathrin proteins attach to recruiter proteins in the membrane.
2. Clathrin proteins polymerize to form a clathrin cage.
3. The clathrin cage forces the membrane to form a rounded bud.
4. The bud is cleaved off to form a clathrin-coated vesicle.
5. The clathrin cage is removed.