Endocytosis and Protein Degradation

Question 1

Phagocytosis

Answer 1

By macrophages/neutrophils which recognize and engulf foreign objects for delivery to the lysosome.
Also recognize apoptotic or aged cells.

Question 2

Pinocytosis

Answer 2

Small volume. Specific uptake of ligands/receptors.

Question 3

2 ways of forming vesicles in pinocytosis

Answer 3

1. ) Clathrin coat proteins

2) Caveolae

Question 4

Adaptor fx?

Answer 4

Cargo binds to TM receptor, this recognizes adaptor –> adaptor complex, allows clathrin coat and budding.
Adaptor cmplx picks correct cargo and membrane proteins.

Question 5

Dynamin

Answer 5

Pinches off vesicle.

Question 6

LDLR

Answer 6

Cholesterol uptake depends on this.
LDLR is re-used. It cycles b/w the surface and lysosome and brings LDL particles to the lysosome where they get degraded.
Turns over every 10 min even w/o cholesterol.

Question 7

LDLR mechanism

Answer 7

LDL particles come in, get clatrhin coated pit, lose coat as it becomes early endosome. Late endosome fuses with lysosome has low pH, causes LDL to dissociate from LDLR.
LDLR recycled to membrane. Cholesterol broken down.
AP2 binds receptor and clathrin. that’s how it gets in pits.

Question 8

Transferrin

Answer 8

Iron. Receptor binds transferrin which has Fe. Endocytosis via clathrin.
Receptor/clathrin recyled.

Question 9

Caveolae

Answer 9

Little cavities.
Small endocytic vesicles without coat proteins.
Important in lipid rafts (lots of cholesterol/signaling mlcs.)
A scaffolding protein for coordinating protein complexes.

Question 10

Caveolin disease

Answer 10

3 genes. Cav-3 in skeletal/cardiac muscle. Mutations cause limb girdle and muscle rippling disease.

Question 11

Viruses and bacteria get into cells how?

Answer 11

Can be doen with clathrin (vesicular stomatitis), caveolin, pinocytosis, phagocytosis (bacteria), fusion

Question 12

3 major protein degradation pathways

Answer 12

1. ) Ubiquitin proteosome system (UPS)
2. ) Lysosome (part of endocytosis path)
3. ) Autophagy (long-lived proteins, entire organelles), role in development of cellular stress like starving

Question 13

Production/elimination balance

Answer 13

They should be equal in the steady state.

Question 14

Why is protein misfolding naughty?

Answer 14

Misfolded proteins don’t work or stick to others via hydrophobic domains —> aggregates

Question 15

Hsp70

Answer 15

Binds hydrophobic regions and prevent aggregation. Bip is Hsp-70 like protein, uses ATP.
During syntehsis
Expand and contract again to get outermost normally folded

Question 16

Hsp60

Answer 16

Isolation chamber to prevent aggregation, refold. Uses ATP to help protein fold in chamber.

Question 17

Calnexin and Calreticulin and Glucosyltransferase

Answer 17

ER resident proteins. Calnexin is TM protein, calretic is in ER lumen.
They bind if sugar is attached (they are lectins). They also bind Ca.
when glucose removed they released, if protein not folded right glucosyltransferase recognized and sugars it… protein can go through many cycles until it folds right or is destined for degradation by being translocated out of the ER. Don’t really know when in cycle this happens.

Question 18

Degradation after failure of cal cycle

Answer 18

proteosome is trash can (1/3 of proteins made get degraded).
Retrotranslocated proteins have multiple ubiquitin mlcs to target to proteosome, are deglycosylated.
Need at least 4 ubiquitins (poly b/c just ubiq not always for degradation).

Question 19

Proteosome

Answer 19

Cylinder. ATP used to unfold protein. Each end of cylinder has a cap that recognizes polyubiquitin.
Ubiqs are recycled, clipped by proteosome.

Question 20

3 ligase enzymes

Answer 20

Nec for attachment of ubiquitis.

E1 (bind and activate ubiq), E2, E3 (specificity, add more ubiq).. ubiq transferred from E2 to E3 via lysine

Question 21

Lysosomes

Answer 21

Mannose-6-P is how the machinery for the lysosome arrives.
Lumen is acidic because of proton pump.
mono-ubiquinated plasma mem proteins are targeted for endocytosis and transferred via late endosome/multivesicular body to lysosome for degradation.
Degrades all classes of molecules.

Question 22

What is prone to lysosomal storage disease?

Answer 22

CNS and PNS

Question 23

Autophagy

Answer 23

eating yourself. Stress response to starvation. Also to degrade organelles.
Double mem forms around organelle, will fuse with lysosome.