Endocytosis Flashcards
Why do cells need endocytosis?
Lipid bilayer is poorly permeable to ions and macromolecules.
• Macromolecules enter only through membrane-bound carriers.
• Endocytosis allows the uptake of external material via plasma membrane invagination and vesicle formation.
What are the main types of endocytosis?
Phagocytosis
- Macropinocytosis
- Clathrin-mediated endocytosis
- Caveolin-mediated endocytosis
What is phagocytosis, and how does it work?
Ingestion/removal of bacteria using receptors that bind antibodies.
Mechanism:
- Receptors bind bacteria → activate F-actin polymerization.
- Plasma membrane protrudes and engulfs the particle (phagosome formation).
- F-actin disassembles.
- Phagosome transported into the cell → fuses with lysosome → content degraded.
How do some bacteria exploit phagocytosis?
They induce their own phagocytosis to enter mammalian cells for nutrients (e.g., bubonic plague).
What is macropinocytosis?
: Uptake of fluid for feeding and removal of large growth factor receptors via actin-driven plasma membrane ruffles.
What are examples of macropinocytosis exploitation?
Bacteria: Salmonella triggers it for uptake.
• Cancer cells: Use it for nutrient uptake.
Q7: What is clathrin-mediated endocytosis?
Receptor-mediated uptake of specific macromolecules (e.g., iron or cholesterol) requiring clathrin and adapter molecules.
What are the two types of receptor-mediated clathrin endocytosis?
- Constitutive receptor-mediated: Continuous uptake (e.g., transferrin receptor for iron, LDL receptor for cholesterol).
- Ligand-induced receptor-mediated: Modulation of signaling (e.g., EGF receptor).
What role do clathrin-coated pits play in endocytosis?
Form a lattice-like structure to facilitate vesicle formation.
What is the mechanism of clathrin-mediated endocytosis?
Adaptin recruits clathrin.
- Dynamin and N-WASP are recruited.
- Arp2/3 causes actin polymerization.
- Vesicle uncoated using auxillin and Hsc70 → clathrin and adaptin released.
What is the function of dynamin?
A large protein that oligomerizes into spirals and is required for vesicle fission.
What is caveolin-mediated endocytosis?
Caveolae (cholesterol and caveolin-enriched invaginations) mediate uptake.
• Caveolin self-associates to form a coat and, with cholesterol, causes membrane invagination.
• Requires dynamin and F-actin.
What is the proposed role of caveolae?
Serve as a plasma membrane reservoir to balance membrane tension.
What role do Rab proteins play in endocytosis?
Regulate compartment specificity.
• Recruit motor proteins for vesicle transport.
• Recruit effectors like SNAREs for targeting and docking.
What are SNARE proteins, and what is their function?
• Transmembrane proteins specific to compartments.
• V- and T-SNAREs form a trans-SNARE complex for vesicle fusion.
• ATPases dissociate cis-SNARE complexes to recycle SNAREs.
