Compartments and Protein Sorting III

Question 1

What is the internal pH of lysosomes?

Answer 1

pH 5

- Acidity maintained by proton motor pump that hydrolyzes ATP to move H+ into the lysosome against its gradient

Question 2

What modification of lysosomal proteins directs them to the lysosome?

Answer 2

A mannose 6-phosphate

Question 3

What is the name of the enzyme that adds the mannose 6-phosphate tag to lysosome hydrolases?

Answer 3

N-acetylglucosamine phosphotransferase

Question 4

Where does the addition of mannose 6-phophate to lysosomal protein occur?

Answer 4

The Endoplasmic Reticulum (ER)

Question 5

What disease is characterized by defects in N-acetylglucosamine phosphotransferase?

Answer 5

I-cell disease

Question 6

What disease is associated with the specific deficiency of the lysosomal hydrolase, Beta-hexaminadase A?

Answer 6

Tay Sachs Disease

- results in the accumulation of GM2 ganglioside (a glycolipid)

Question 7

What disease is associated with the deficiency of the lysosomal hydrolase, glucocerebroside?

Answer 7

Gaucher’s Disease

Question 8

By what mechanisms can extracellular material be delivered to lysosomes?

Answer 8

Phagocytosis and endocytosis

Question 9

What type of cells are primarily involved in phagocytosis?

Answer 9

White blood cells (Macrophages and Neutrophils)

Question 10

The term used for the expansion of the plasma membrane around a particle during phagocytosis?

Answer 10

Pseudopod

Question 11

The formation of the Pseudopod is dependent on what?

Answer 11

Microfilaments (Actin) underneath the plasma membrane

Question 12

How do some bacterium such as Mycobacterium, and Salmonella avoid degradation by lysosomes within a cell?

Answer 12

They prevent the fusion with the lysosomes

Question 13

What are the two types of Endocytosis?

Answer 13

1. Pinocytosis

2. Receptor-mediated endocytosis

Question 14

What characteristics distinguish pinocytosis from receptor-mediated endocytosis?

Answer 14

Pinocytosis is nonspecific and non-saturable

Receptor-mediated is specific and saturable

Question 15

Where does endocytosis usually occur?

Answer 15

At coated pits

Question 16

What is the function of clathrin proteins and where are they located?

Answer 16

They drive the inward budding of the plasma membrane during endocytosis and they are located on the cytoplasmic side of coated pits

Question 17

Other than at coated pits, where else can endocytosis occur?

Answer 17

At caveolae

Question 18

What is the protein that makes up the coat of Caveolae?

Answer 18

Caveolin

Question 19

Where are Caveolae most abundant? What do they endocytose?

Answer 19

Abundant in epithelial cells. The primarily uptake lipids

Question 20

What secures clathrin proteins to the cytoplasmic side of the plasma membrane?

Answer 20

Adaptin proteins

Question 21

What is the name of the GTPase that wraps around the neck of the invaginated vesicle and pinches it off from the plasma membrane?

Answer 21

Dynamin

Question 22

T or F: LDL dissociates from the LDL receptor once inside the early endosome?

Answer 22

True

Question 23

T or F: LDL receptors are recycled back to the cell surface?

Answer 23

True

Question 24

What causes the disease, Familial Hypercholesterolemia?

Answer 24

Mutations in the LDL-receptor that prevents the binding of adaptins, and consequently the prevention of endocytosis of LDL
- results in high serum cholesterol that leads to atherosclerosis

Question 25

What do adaptin proteins bind to?

Answer 25

LDL-Receptors and clathrin

• Adaptin proteins are attached to the cytosolic side of LDL-receptors and once LDL binds, they recruit and bind clathrin proteins

Question 26

T or F: EGF dissociates from the EGF-Receptor once inside the early endosome

Answer 26

False

• EGF remains bound to the EGF-Receptor

Question 27

T or F: EGF-receptors are recycled back to the cell surface

Answer 27

False

• EGF remains bound to the EGF-receptor and BOTH are degraded in the lysosome

Question 28

The diphtheria toxin is dependent on what type of cell surface coat?

Answer 28

Diphtheria toxin endocytosis is clathrin-dependent

Question 29

Which chain of the Diphtheria toxin binds to the receptor?

Answer 29

The B-chain

Question 30

Once endocytosed, how does the diphtheria toxin enter the cytoplasm?

Answer 30

The B-chain dissociates from the receptor and creates a pore in the endosome through which the A-chain enters the cytoplasm and inhibits protein synthesis

Question 31

Cholera toxin is dependent on what type of surface coat?

Answer 31

Cholera toxin endocytosis is caveolae-dependent

Question 32

What protein found on the membrane enveloping the influenza virus is responsible for the binding with host cell receptors?

Answer 32

Hemagglutin

Question 33

What cell surface coat is associated with the endocytosis of the influenza virus?

Answer 33

clathrin

Question 34

How does the genetic material of the influenza virus enter the cytoplasm?

Answer 34

The low pH of the endosome triggers the fusion of the viral membrane with the endosome membrane which then releases the genetic material into the cytoplasm

Question 35

By what method does HIV enter the cell?

Answer 35

By direct fusion with the plasma membrane

-HIV does not require endocytosis

Question 36

At what pH does direct fusion of HIV occur?

Answer 36

Neutral pH