Cell: endocytosis

Question 1

What are the 3 fates endocytosed material can have?

Answer 1

Degredation
Transcytosis
Recycling

Question 2

Give some examples of endocytic pathways

Answer 2

Macropinocytosis
Phagocytosis

Question 3

Describe phagocytosis

Answer 3

→ used to recognise apoptotic cells, bacteria and engulf
- Often used by immune cells e.g macrophages (but other cells can be induced)
- Uptake of large molecules
- Pathogens are often coated by antibodies (opsonization) which are recognised by phagocytes

Question 4

What is frustrated phagocytosis?

Answer 4

When 2 cells are trying to engulf the same bacterium
= Shows fusion of pseudopods is cell autonomous
Can be used as an experimental tool

Question 5

Describe the first experiment on membrane recycling

Answer 5

Macrophages phagocytosed 1.1uM latex beads
By counting the beads it was possible to estimate how much membrane was internalised

Results:
30% of total SA internalised per hour
But no change in cell size
= Therefore membrane must be recycled

Question 6

Describe Macropinocytosis

Answer 6

• Cells firm active driven ruffles which sometimes fuse to form macropinosomes
• Mechanistically similar to phagocytosis
• Non selective uptake of extracellular material
• Used by immune cells e.g dendrites, macrophages to ‘sample’ envrion
• Used by cancer cells to take up nutrients

Question 7

Describe clathrin-mediated endocytosis

Answer 7

• LDL receptors clustered into clathrin coated pits
• Pit forms coated vesicle containing LDL + receptor
• Vesicle uncoats to fuse with endosome
• Early endosome (important in sorting carbs) → lower pH than cytoplasm
• Receptor recycled to membrane
  -LDL sent to lysosome and broken down

Question 8

Why do adapter proteins join onto clathrin triskelia?

Answer 8

Adapter proteins bind to the heavy chains of the triskelia, facilitating the binding of transmembrane receptors e.g LDL receptors

Question 9

What type of structure do clathrin treskelia self-assemble into?

Answer 9

spherical lattices

Question 10

Which GTPase is required to pinch off the clathrin coated vesicles?

Answer 10

Dynamin

Question 11

Why is pH important in the endocytic pathway?

Answer 11

LDL needs lower pH to dissociate from receptor
Lysosomes need low pH
Rab5 proteins help SNAREs to mediate fusion

Question 12

What is the late endosome known as?

Answer 12

Multivesicular Body (MVB)