endocytosis and exocytosis Flashcards
N linked, O linked glycoproteins and proteoglycan synthesis
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
glycoaminoglycan
- repeating disaccharide 100 sugars long
- negatively charged
degradation of proteoglycans and glycoproteins
- 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
ABO blood type
- depends on oligosacchardie portion of glycoprotein on RBC
- codes for certain glycosyltransferase that delivers:
- GA1 Nac - A antigen
- GA1 -B antigen
- nothing - O antigen
constituitive vs regulated exocytosis
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
Phagocytosis
- 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
receptor mediated endocytosis
-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
early and late endosome
early - near PM. sorting station for endocytosis. pH 6
late - near nucleus. delivers cargo to lysosome or becomes a lysosome
endocytosis pathways
- recycle- to PM
- degrade - in lysosome
- transcytosis - in onemembrane domain and out another. like Ab to breast milk from blood
lysosome structure and function
- 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:
- endocytosis
- phagocytes
- autophagy - obsolete cell parts build themselve a membrane and fuse with endosome or lysosome
human lysosomal storage disease
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