Compartments and Protein Sorting III Flashcards
What is the internal pH of lysosomes?
pH 5
- Acidity maintained by proton motor pump that hydrolyzes ATP to move H+ into the lysosome against its gradient
What modification of lysosomal proteins directs them to the lysosome?
A mannose 6-phosphate
What is the name of the enzyme that adds the mannose 6-phosphate tag to lysosome hydrolases?
N-acetylglucosamine phosphotransferase
Where does the addition of mannose 6-phophate to lysosomal protein occur?
The Endoplasmic Reticulum (ER)
What disease is characterized by defects in N-acetylglucosamine phosphotransferase?
I-cell disease
What disease is associated with the specific deficiency of the lysosomal hydrolase, Beta-hexaminadase A?
Tay Sachs Disease
- results in the accumulation of GM2 ganglioside (a glycolipid)
What disease is associated with the deficiency of the lysosomal hydrolase, glucocerebroside?
Gaucher’s Disease
By what mechanisms can extracellular material be delivered to lysosomes?
Phagocytosis and endocytosis
What type of cells are primarily involved in phagocytosis?
White blood cells (Macrophages and Neutrophils)
The term used for the expansion of the plasma membrane around a particle during phagocytosis?
Pseudopod
The formation of the Pseudopod is dependent on what?
Microfilaments (Actin) underneath the plasma membrane
How do some bacterium such as Mycobacterium, and Salmonella avoid degradation by lysosomes within a cell?
They prevent the fusion with the lysosomes
What are the two types of Endocytosis?
- Pinocytosis
2. Receptor-mediated endocytosis
What characteristics distinguish pinocytosis from receptor-mediated endocytosis?
Pinocytosis is nonspecific and non-saturable
Receptor-mediated is specific and saturable
Where does endocytosis usually occur?
At coated pits
What is the function of clathrin proteins and where are they located?
They drive the inward budding of the plasma membrane during endocytosis and they are located on the cytoplasmic side of coated pits
Other than at coated pits, where else can endocytosis occur?
At caveolae
What is the protein that makes up the coat of Caveolae?
Caveolin
Where are Caveolae most abundant? What do they endocytose?
Abundant in epithelial cells. The primarily uptake lipids
What secures clathrin proteins to the cytoplasmic side of the plasma membrane?
Adaptin proteins
What is the name of the GTPase that wraps around the neck of the invaginated vesicle and pinches it off from the plasma membrane?
Dynamin
T or F: LDL dissociates from the LDL receptor once inside the early endosome?
True
T or F: LDL receptors are recycled back to the cell surface?
True
What causes the disease, Familial Hypercholesterolemia?
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
What do adaptin proteins bind to?
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
T or F: EGF dissociates from the EGF-Receptor once inside the early endosome
False
- EGF remains bound to the EGF-Receptor
T or F: EGF-receptors are recycled back to the cell surface
False
- EGF remains bound to the EGF-receptor and BOTH are degraded in the lysosome
The diphtheria toxin is dependent on what type of cell surface coat?
Diphtheria toxin endocytosis is clathrin-dependent
Which chain of the Diphtheria toxin binds to the receptor?
The B-chain
Once endocytosed, how does the diphtheria toxin enter the cytoplasm?
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
Cholera toxin is dependent on what type of surface coat?
Cholera toxin endocytosis is caveolae-dependent
What protein found on the membrane enveloping the influenza virus is responsible for the binding with host cell receptors?
Hemagglutin
What cell surface coat is associated with the endocytosis of the influenza virus?
clathrin
How does the genetic material of the influenza virus enter the cytoplasm?
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
By what method does HIV enter the cell?
By direct fusion with the plasma membrane
-HIV does not require endocytosis
At what pH does direct fusion of HIV occur?
Neutral pH
