Endocytosis

Question 1

Describe pinocytosis

Answer 1

All cells, constitutive, form pinosomes. Stimulated by growth factors and other signals. Used for bulk nutrient uptake (solutes and proteins)

Question 2

Describe action of pinocytosis

Answer 2

Actin remodels cytoskeleton to form protrusions which close and vesicles move along microtubules to cell center

Question 3

Describe Phagocytosis

Answer 3

Specialized cells used inc macrophages, PMN, Dendritic cells. Receptoy triggered by Clathrin independent. Uses opsonins

Question 4

What are opsonins and their action

Answer 4

Proteins such as complement, antibodies, bact oligo, apoptotic cell memb. Bind to receptors on phagosomes and brought to lysosome

Question 5

What are the phases of phagocytosis

Answer 5

1. Attachment: phag to opsonin
2. Engulfment: actin filament assembly to fuse to phagosome
3. Fuse with lysosome: microtubules and motor proteins direct phag to lys. Fusion involves RAB, Snares, SNAP and NSF
4. Digestion: Lys H-lytic enzymes leads to residual bodies

Question 6

Describe receptor mediated endocytosis Clathrin

Answer 6

Receptors cluster, bind to target, initiate formation of clathrin coated pits. Adaptin interacts with cyto sorting signal and C-R concentrate cargo

Question 7

Describe the pathway of clathrin coat endocytosis

Answer 7

Cargo - C-R - adaptin - clathrin - Dynamin (close vesicle) - RAB assisted release of clathrin exposing v snare - tsnare and docking mech

Question 8

Describe RME - Chol

Answer 8

LDL - LDL-R - adpatin - clathrin - Dynamin - endosome - low pH (LDL dissoc from LDL-R) - lysosome - free chol

Question 9

Describe Caveolin

Answer 9

Not well understood, integral membrane protein and spikey

Question 10

What is familial hypercholesterolemia

Answer 10

Mut in LDL-R increasing plasma chol and chol synthesis. Class 4 = not located in pits (LDL-R) so ineffective endocytosis