L13: Endocytosis & Intracellular Vesicle Trafficking

Question 1

Define endocytosis

Answer 1

Process of uptake of outside materials by invagination of the plasma membrane followed by pinching off & intracellular vesicle formation

Question 2

Function of phagocytosis

Answer 2

Ingestion & removal of bacteria

Question 3

Mechanism of phagocytosis

Answer 3

1) Receptors that bind bacteria become activated
2) F-actin polymerisation is also activated
3) More receptors bind more ligand molecules, cell membrane engulfs target
4) Phagosome formed
5) F-actin disassembles
6) Phagosome fuses with lysosome= phagolysome
7) Digestion of target

Question 4

Function of macropinocytosis

Answer 4

Uptake of fluid for feeding & removal of large no. of growth factor receptors from plasma membrane

Question 5

Macropinocytosis

What does growth factor stimulate ?

Answer 5

Stimulate actin driven protrusion of plasma membrane called ruffles taken up by large vesicles

Question 6

Use of macropinocytosis in cancer cells

Answer 6

Nutrient uptake

Question 7

3 types of receptor-mediated endocytosis

Answer 7

1. clathrin-mediated
2. non-clathrin-mediated
3. caveolin-mediated

Question 8

Function of clathrin-mediated endocytosis

Answer 8

Receptor-mediated that allows cells to take up specific macromolecules not abundant in the extracellular fluid

Question 9

What molecules does clathrin-mediated endocytosis require?

Answer 9

Requires clathrin & adapter molecules

Question 10

2 receptor mediated endocytosis in clathrin-mediated endocytosis

Answer 10

1) Constitutive receptor mediated
2) Ligand induced receptor mediated

Question 11

Structure of clathrin

Answer 11

Clathrin forms 3-legged structures

Question 12

Mechanism of Clathrin-mediated endocytosis

Initiation

Answer 12

Specific ligands bind to receptors on cell membrane

Question 13

Mechanism of Clathrin-mediated endocytosis

Bud formation

Answer 13

Binding triggers recruitment of clathrin proteins which forms a basket around membrane where receptors are located

Question 14

Mechanism of Clathrin-mediated endocytosis

Invagination

Answer 14

Clathrin-coated pit begins to invaginate to create a deep pocket- to form a vesicle

Question 15

Mechanism of Clathrin-mediated endocytosis

Vesicle formation

Answer 15

Dynamin (GTPase enzyme) wraps around the neck of the invaginated pit

Dynamin constricts & hydrolyses GTP

Question 16

Mechanism of Clathrin-mediated endocytosis

Vesicle uncoating

Answer 16

After vesicle is formed, clathrin is rapidly removed from its surface, allowing vesicel to fucse with early endosomes

Question 17

Mechanism of Clathrin-mediated endocytosis

Cargo processing

Answer 17

Vesicle delivers its cargos to lysosomes for degradation

Question 18

How does caveolin cause membrane invagination?

Answer 18

It self-associates to form a coat & with cholesterol in the membrane causes invagination

Question 19

What are SNAREs?

Answer 19

Transmembrane proteins

Question 20

What are SNARE’s recruited by?

Answer 20

Rab’s

Question 21

What does v-SNAREs & t-SNAREs on opposing membranes form?

Answer 21

trans-SNARE complex

Question 22

What does Rab-GTP recruit?

Answer 22

Motor proteins that transport carriers on actin filaments/microtubules