Receptors and Endocytosis

Question 1

Define endocytosis

Answer 1

Transport of molecule into cell by membrane invagination

Question 2

What does phagocytosis need?

Answer 2

Specialised cells (specific)

Question 3

What is receptor-mediated endocytosis?

Answer 3

Any specific cell

Question 4

What is pinocytosis?

Answer 4

Any non-specific cell

Question 5

What are the steps of phagocytosis?

Answer 5

Recognition/Adherence/Engulfment/Digestion

Question 6

Name some specialised cells linked to phagocytosis

Answer 6

Macrophages, Neutrophils

Question 7

Describe the process of phagocytosis

Answer 7

Only by specialised cells

Pathogen associated molecular pattern (PAM’s) binds with a Toll-like receptor

Question 8

Describe the structure of clathrin molecules

Answer 8

Macromolecular cages
Composed of three-legged units (triskelions)
Lattice of hexagons/pentagons (soccer ball)

Question 9

What do clathrin-coated vesicles transport?

Answer 9

selected integral membrane proteins from cell surface and trans-Golgi network to endosomal system

Question 10

In terms of scission, What is dynamin?

Answer 10

Large GTPase involved in budding, scission nascent vesicles from parent membranes

Question 11

What is bin-amphiphysin-rvs (BAR)?

Answer 11

Proteins bind to membrane, sculpt the curvature

Question 12

Describe BAR

Answer 12

Domain is one of the main links btw membranes/actin cytoskeleton
BAR proteins sense membrane curvature, recruit actin to membranes, interact with GTPase dynamin which mediates vesicle fission

Question 13

Describe the energy dependent step (uncoating)

Answer 13

Auxilin binds with high affinity to assembled clathrin lattices with ATP
Together they distrupt protein-protein interactions in clathrin lattice

Question 14

What are SNARE proteins?

Answer 14

Soluble protein receptors

Question 15

Describe the function of SNARE proteins

Answer 15

Mediate fusion of vesicles structures

Vesicle deliver cargo to target membrane bound structures

Question 16

What do SNARE proteins tether?

Answer 16

Target membrane and vesicle, support fusion

Question 17

What can be formed from SNARE proteins?

Answer 17

Vesicle and target SNARE proteins form tight a-helical bundle - SNARE complex disassembled and recycled

Question 18

In terms of SNARE disassembly, what is cytoplamic?

Answer 18

NSF is thought to disassemble the SNARE complex using ATP as an energy source

Question 19

Describe the clathrin-independent process and what it contributes to

Answer 19

Major contributor to fluid uptake in cells/membrane repair

Contributes to cellular polarisation, motility, regulation of signalling, normal cell growth

Question 20

What are the mechanisms involved with clathrin-independent processes?

Answer 20

Caveolae - Involves caveolin/lipid rafts

Macropinocytosis - Large vesicles

Question 21

Describe what happens after internalisation

Answer 21

Fusion with early endosomes, Importance of pH

Different processing pathways - Recycling to plasma membrane, Degradation by lysosomal enzymes, Transcytosis

Question 22

Name some examples of delivery of cholesterol and iron to tissues

Answer 22

Low density lipoprotein (LDL)
Transcytosis of antibodies
Familial hypercholesterolaemia - Autosomal dominant genetic disorder by chr19 mutation = Defect in LDL receptor, causes high level of LDL in blood

Question 23

Describe transferrin

Answer 23

Carries iron in blood, lower pH in endosome causes trans to release its iron, receptor recycled into plasma membrane, dissociates from receptor when in pH7 outside cell

Question 24

Describe transcytosis

Answer 24

Movement of macromolecules btw cells (across endo of blood vessels)
For caveolae/clathrin-mediated processes, Regulates SNARE proteins, cytoskeleton, lipids