Lecture 7
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Endosomes Converges what? Property?
Converges biosynthetic and endocytic pathway -low pH of 6 -is the recycling and sorting compartment
Why does endosomes have low pH and what is it’s function?
Low pH is caused by the proton pump which acidifies the content. Low pH promotes dissociation of receptors and their ligands
what is LDL
LDL is low-density lipoproteins, they carry cholesterol to be used for biosynthesis
Hypothesis for endosome compartments
Stable which transfers down cargo vesicle and bring back empty ones Maturation is where early fuses to late fuses to lysosomes and recycles vesicle back u
Horseradish Peroxidase and what does it catalyze?
-good for tracing -catalyze polymerization of DAB which forms a product that is visible with EM
Heterotypic Fusion
Fusion of compartments with different composition eg. vesicle to ER
Homotypic
Fusion of same composition compartments eg. Golgi to Golgi
Homotypic Fusion involves?
Rab GTPase with GEF, tethers, SM and R- and Q-SNAREs
Multivesicular Bodies or late endosomes
Internalized molecules for degradation becomes packaged into large spherical structures
2 main functions of Light Microscopy
Magnify and add contrast
Refraction
Is when light’s velocity changes when medium changes
How does oil immersion increase resolution?
It allows light to not have internal reflection and focuses the rays to just inside the immersion compared to just air
Phase-Contrast Microscopy
Enhances phase shift by increase interference. Different protein concentration have different refractive index
Do late endosomes mature or fuse into lysosomes?
Experiment was used to confirm that late endosomes FUSE HRP was used to chase. All HRP was internalized by lysosomes which are then inactivated by DAB. All late endosomes were not maturing and could not fuse.
How do endosomes sort?
Geometry and biochemically
Rab conversion
GDI recruits Rab5 to early endosome, switches or recruits Rab7 with HOPS as tether and is bound to late endosome
Retromer
Coat-like endosome sorting device Transports to TGN “coils” brings back CI-MPR to TGN
ESCRT complexes recognizes? function?
-recruited to endosomes -recognizes ubiquitylated transmembrane proteins -pass cargo to next complex to MVB vesicles -like a conveyor belt
ESCRT III
-its assembly drives vesicle formation -assembly is driven by Vsp4 -is like a drill
Vps4 what part of family? Drives what and how?
AAA+ ATPase Associated with diverse cellular Activities Drives formation of intraluminal vesicles with the formation of ESCRT-III its polymerization is like a tug-of-war- driven by Vps4 ATP hydrolysis in every new subunit
3 things that happen to internalized vesicles
-Degradation to lysosmes -Storage (like MHCII) -exosome release