endocytosis and exocytosis

Question 1

N linked, O linked glycoproteins and proteoglycan synthesis

Answer 1

N link glycoproteins - added in ER, modified by glycosyl transferase in golgi. 3 classes: mannose, complex, hybrid

O link glycoproteins - Add OH to threonine and serine. adding sugars one at a time (N linked is added at once then modified). done post translationally

proteoglycan synthesis - 95% carb. must contain glycoaminoglycan (varying amounts)
-protein core made in ER, sugars added in golgi or ER
3 types of glycosylation
1. o linked glycosaminoglycan
2. o linked oligosaccharide
3. N linked oligosaccharide

Question 2

glycoaminoglycan

Answer 2

• repeating disaccharide 100 sugars long

- negatively charged

Question 3

degradation of proteoglycans and glycoproteins

Answer 3

• by hydrolases (protease and gllycosidase) in lysosome
  1. glycosidase removes carb
  2. protease cleaves peptide
  3. glycosidase removes sugars in opposite way they were added

Question 4

ABO blood type

Answer 4

• depends on oligosacchardie portion of glycoprotein on RBC
• codes for certain glycosyltransferase that delivers:
• GA1 Nac - A antigen
• GA1 -B antigen
• nothing - O antigen

Question 5

constituitive vs regulated exocytosis

Answer 5

constituitive: default. always going on and happens unless signal says otherwise
regulated: proteins from golgi into secretory vesicles and wait by PM for signal to be released

Question 6

Phagocytosis

Answer 6

• ingest large particles by phagosomes
• need receptors
• alternate to pinocytosis which is all the same for small molecules
• WBC, neutrophils, macrophages
• when induced extends PM and engulfs to form phagosome, which binds lysosome for degradation

Question 7

receptor mediated endocytosis

Answer 7

-bind receptors on PM to recruit clathrin coated bits and enguld coated vesicles. makes pinocytosis efficient.
LDL example
-need cholesterol for membrane synthesis
-cholesterol is in LDL particles
-LDL receptors on PM associate with clathrin proteins and bring LDL vesicle in
-shed clathrin in endosome, LDL receptor disociates
-LDL frees cholesterol once inside llysosome
-Familial hypercholesterolemia - LDLreceptors are block and build plague in blood. kids get heart attacks

Question 8

early and late endosome

Answer 8

early - near PM. sorting station for endocytosis. pH 6

late - near nucleus. delivers cargo to lysosome or becomes a lysosome

Question 9

endocytosis pathways

Answer 9

1. recycle- to PM
2. degrade - in lysosome
3. transcytosis - in onemembrane domain and out another. like Ab to breast milk from blood

Question 10

lysosome structure and function

Answer 10

• 40 acid hydrolases
• ATP pump keeps pH at 5
• degraded products back to cytosol
• proteins that make up lysosome are glycosylated to protect themselves from harsh environment
• lysosomal protein and enzymes made in ER. tagged with M6P msrker and in trans golgi get packed into vesicles that will be transported to lysosome by an endosome

3 paths to lysosome:

1. endocytosis
2. phagocytes
3. autophagy - obsolete cell parts build themselve a membrane and fuse with endosome or lysosome

Question 11

human lysosomal storage disease

Answer 11

defective hydrolases

• undigested glycoproteins and proteoglycans accumulate
  a. Inclusion cell disease - enzymes for M6P marker missing. hydrolases are secreted. undigested substrate accumulate

b. mucopolysaccharidoses - enzyme for glycosamnoglycan degradation defect. build up in lysosomes, blood, tissues (Hurler syndrome)
c. oligosaccharidoses - cant degrade oligosaccharides. cause facial dysmorphia and mental retardation. Schindler disease
d. sphingolipidoses - cant degrade sphingoliids. build up in macrophages in lver, spleen, bone marrow. Gaucher and Tay Sachs disease