Endocytosis and Protein Degredation

Question 1

Two methods of endocytosis

Answer 1

1. phagocytosis

2. pinocytosis

Question 2

How does the cell get cholesterol from the environment?

Answer 2

LDLR binds LDL

Then endocytosed via clathrin coated vesicle formation (with adaptor protein binding cargo )

Question 3

Describe two major routes for small volume endocytosis.

Answer 3

1. clathrin coated vesicles

2. caveolae

Question 4

How does the cell get iron into the cell?

Answer 4

Transferring receptor binds Iron. Then endocytosed via clathrine coated vesicle.

Question 5

Caveolae formation. Give examples of what utilizes it

Answer 5

Doesn’t use protein coats. Form endocytic vesicle like- thing at plasma membrane.

Utilized by cholera toxin, albumin ect.

Question 6

Describe two types of molecular chaperones.

Answer 6

1. Hsp70

2. Hsp60

Question 7

Hsp70

Answer 7

binds to exposed hydrophobic patches of incompletely folded proteins to prevent aggregation

Question 8

Hsp60

Answer 8

forms large, barrel shaped structure that acts as isolation chamber

misfolded proteins are fed into it to prevent aggregation and promote proper refolding

Question 9

4 examples of how quality control of protein synthesis ensured in the ER.

Answer 9

1. ER provides optimized oxidizing environment
2. folding enzymes
3. chaperones - ATPases
4. Folding sensors

Question 10

How does the ER provide an optimized oxidizing environment?

Answer 10

The oxidizing environment is optimal for folding of the protein and oligomeric assembly

Question 11

What is an example of folding control used in ER quality control?

Answer 11

formation of disulfide bonds

Question 12

What is an example of molecular chaperones-ATPase used in ER quality control?

Answer 12

BiP - HSP70 family

keeps protein from aggregating when it is being formed

Question 13

What is an example of folding sensors used in ER quality control?

Answer 13

UDP-glucose:glycoprotein glucosyltransferase (UGGT)

Question 14

Describe the proteasome, protein degradation, and the role of ubiquitin.

Answer 14

proteosome: garbage/recycling protein

ER is monitored - misfolded proteins are detected, translocated back into the cytosol to be deglycosylated, ubiquitylated, and degraded in proteosomes.

Question 15

Ubiquitination:

what is it and what are the steps?

Answer 15

Covalent attachment of ubiquitin (conserved sequence) to acceptor lysine in protein to be degraded.

steps:
1. E1 ubiquitin - activates ubiquitin
2. E2 ubiquitin - takes activated ubiquitin and transfers it to E3
3. E3 ubiquitin - protein ligating enzyme that binds directly to substrate and covalently attaches ubiquitin to substrate
4. Binding of 1 ubiquitin = causes more to bind
5. Proteosome removed ubiquitins and murders the hell out of the protein

Question 16

How are lysosomes regulated?

Answer 16

degrades all cellular components

1. targeted via endocytic pathway
2. Monoubiquitinated transmembrane proteins
3. regulated at multivesicular body: contains prelysosomal compartment and fuses with lysosome

Question 17

Examples of lysosomal storage diseases

Answer 17

1. Tay sachs
2. gaucher’s disease
3. Niemann-Pick

Question 18

Tay-Sachs:

Answer 18

beta-hexosaminidase, breaks down gangliosides in neurons

Question 19

Gaucher’s disease

Answer 19

beta-glucosidase, breaks down glucosylceramide in monocytes and leukocytes

Question 20

Niemann-Pick

Answer 20

(1) sphingomyelinase, breaks down sphingomyelin in macrophages
(2) cholesterol transporter, moves cholesterol from the lysosome to the cytosol.