Endocytosis

Question 1

Receptor mediated endocytosis

Answer 1

Uses receptors to bind specific ligands

Receptors are enriched within coated pits, and the endosomes become enriched for the ligand

Question 2

Late endosomes

Answer 2

When the endosomes become acidified and enriched with acid hydrolases

Will ultimately become lysosomes

Question 3

Phagocytosis

Answer 3

Evagination of the plasma membrane

Engulfing foreign particles such as bacteria or viruses

Internalizing them in membrane-enclosed phagosomes

Question 4

Autophagy

Answer 4

Removal of organelles into autophagosomes for digestion

Get rid of old organelles

Under conditions of starvation, cells can digest organelles as a stress response

Increases in neural injury, neurodegeneration

Can destroy intracellular pathogens

Question 5

AP2 protein role in receptor mediated endocytosis

Answer 5

Integral receptor (or cargo) is bound to the AP2 protein

AP2 reacts with clathrin

Question 6

Once AP2 reacts with clathrin (endocytosis)

Answer 6

ARF promotes the de-coating of clathrin

Early endosome is now formed

Gains other proteins (acid hydrolases, ATP-dependent proton pump) through vesicular trafficking from the TGN

—> late endosome

Question 7

What causes the endosome to get more acidic

Answer 7

ATP dependent proton pump

—> becomes lysosome

…ligand receptor complexes will dissociate and either recycle to the plasma membrane or degrade in the lysosome

Question 8

LDL ligand for RME

Answer 8

ApoB

On the outer surface of the LDL

High affinity for the LDL receptor at physiological pH

Once pH lowers in endsome/lysosome…LDL receptor releases LDL so it can be broken down

Then its recycled back to the plasma membrane so it can take up another LDL

Question 9

Familial Hypercholesterolemia

Answer 9

Elevation of LDL in blood

Mutation in LDL receptor (could be in alot of ways that the receptor or the process of the LDL uptake is defective)

Question 10

Ferrotransferrin

Answer 10

Fe3+ and transferrin protein

The complex in which iron is transported to cells

Question 11

Apotransferrin

Answer 11

Transferrin in the absence of iron

Question 12

Transferrin receptor

Answer 12

What cells use to recognize and take up iron (ferrotransferrin)

High affinity at normal pH

Low pH —> lets go of ferrotransferrin

Question 13

How apotransferrin is release out of cell once iron is released from it in the lysosome

Answer 13

Low pH = high affinity for transferring receptor

Recycled back to plasma membrane

Normal pH = low affinity…released

Question 14

Situations when the cell would want to break down the membrane of vesicle and the integral proteins

Answer 14

1. Certain receptors are not recycled and degraded
2. Some proteins get worn out in golgi and need to be degraded

In such cases…the membrane and proteins invaginate into lysosome and become vesicular bodies

Then degraded when acid hydrolases become active

Question 15

Hrs proteins and ESCRT complex (lysosomal invagination)

Answer 15

1. Hrs protein and the proteins for degradation…become monoubiquitinated
2. Interact with ESCRT complex to induce invagination
3. ESCRT are recycled after degradation of proteins

Question 16

Budding of HIV particles

Answer 16

HIV Gag protein is analogous to the Hrs protein in lysosomal invagination process

Become monoUbq-ed and serve as a scaffold for the EXCRT assembly

However result = evagination

***Gag protein is part of the HIV envelope