cell bio 2c
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what kind of proteins with what kind of signals are transported to lysosomes?
glycoproteins, mannose-6-P chains
what is the purpose of acid hydrolases in acidic organelles?
breakdown of endocytosed substances and turnover of organelles
how does the cell know to target lysosome?
- phosphorylate N-linked mannose sugars
- recognized by man6-P receptors (integral membrane proteins)
- recognized by adaptors
- pH sensitive release in endosome/lysosome
- man 6-P receptors are recycled to Golgi
what is the lysosome involved in?
digestion of phagoctosed substances and turnover of organelles by autophagy
what is phagocytosis?
engulf and ingest bacteria by phagosome
what is autophagosome?
membrane forms bilayer around organelle to autophasome to lysososme to be degraded
what types of pathway are secretory proteins targetted for?
regulated and consitutive secretion in trans-Golgi
how do secretory granules mature?
- immature secretory granule buds off
- gets more dense as it matures: v type ATPase decrease pH allows proteins to condense and concentrate.
- Mature granules wait near the plasma for signal, fusion of vesicle and secretion
- proteins not suppose to be in secretory material sent to sorting endosome
what are the terminal steps in calcium triggered membrane fusion during secretion?
- ATP-dependent priming
- Ca sensors: CAP-calcium activating protein for secretion (priming)
- synaptotagmin-will halt fusion until signal
what are the three pathways to distribute integral membrane proteins to apical or basolateral plasma membrane?
- direct sorting from TGN (lipid raft)
- indirect (apical and basal go to basal, then apical go to endosome to lysosome)
- indirect via transcytosis (both basal and apical go to basal, then apical goes to sorting endosome and apical
what is the function of the Golgi in relation to secretory membrane system?
- carbohydrate processing
- protein sorting
- sphingomylein and glycosphingolipid synthesis
at what phase does the Golgi fragment start to break up? and when does it appear again?
what is the function of microtubles?
- maintains focused Golgi
- disruption leads to loss of Golgi and fragmentation
how are proteins transferred through the endomembrane system?
- transferred in vesicles
- coat proteins and dynamin drive vesicle formation
- transmembrane SNARE proteins ensure targeting specificity
- coats are removed prior to membrane fusion achieve with SNAREs
what does phagocytosis, Clathrin-mediated uptake and Macrophinocytosis need?
phosphoinositides in endocytic compartments
what are the different mods of endocytosis?
- macropinocytosis *scoop and engulf
- Clathrin-coated vesicle
- non-coated vesicle
- caveolae *lipid raft areas
- phagocytosis *engulfmemt
**Calthrin and cavelao are tightly regulated by recognition of signal
what are the mechanisms of phagocytosis?
- attachment: recognizes foreign body using protein receptors; actin polymerization
- engulfment: phagocytic cup uses to engulf bacteria, membrane from endosome allows it to recycle plasma membrane and phagosome matures
- fusion: with lysosome lower pH to 4-5 (proteosis)
what is the function of actin in the mechanism of phagocytosis?
- push membrane forward as it forms a cup around bacteria
- actin is used to push bacteria away from plasma membrane
what is PI (4,5)-P2 important for?
phagocytosis, clatherin mediated uptake, macrophinocytosis
How do endothelial cells take up nutrients? what are the invaginations in endothelial cells called?
caveolin, which makes up coat of caveolae, invaginations called little caves
where does caveloin bind and stabilize?
binds cholestrol and stailizes lipid rafts, immobile in membrane, also uses dynamin
what is the difference between Clarithin and COP vs. caveolin?
Clathrin and COP gets recruited by adaptor proteins while caveolin is immobile in membrane
what are the protein components of coated vesicles?
AP2, Clathrin, Dynamin
what is the role of AP2?
alpha and beta subunits; beta subunit recruits invaginating factors
what is the role of the micro chain on AP2
it is an adaptor protein that interacts with Clathrin; forms Clathrin cage
how does Clathrin come together?
the hub connects to two light chains
describe the process of receptor mediated endocytosis by coated vesicles
- AP2 recruitment (AP2 nd Clathrin)
- coat assembly and curvature
- coated pit formation
- dynamin collar constriction: amphiphysin and dynamin
- uncoating for transport
what is the role of synaptojanin in receptor mediated endocytosis?
dephosphorylates PI(4,5)P2 to PI(4)P and the coat falls off
what is the role of amphiphysin in receptor mediated endocytosis?
interacts with AP2 and recruits dynamin
what does Clathrin coated vesicle formation requires?
- Cargo receptors
- coat proteins
what does GTPase dynamin provide?
energy to release vesicles
what is the role of adaptor proteins?
bind cytoplasmic tails to sort and concentrate
what are the antibodies to the LDLs labeled as?
describe the processes of LDLs
- apolipoprotein binds to receptor
- binding gets adaptor protein AP2
- get Clathrin
- dephosphorylation of PI (4,5)P2 (invagination)
- vesicles goes to endosome (ph6)--pH change causes receptor to dissociate
why does LDL end up in the lysosome?
gets chewed up into cholesterol components (spit out for cells to use as free cholesterol)
what is the difference between an early and late endosome?
EE has pH 6, late endosome pH 5
what is the rate of membrane internalized per minute?
2-20% of membrane internalized per minute
what is transferrin and is it released at low pHs?
transferrin binds tightly to iron receptors and is not release when Fe is release, it goes back to membrane with iron receptor
how do endosomal membrane have pH and functional differences?
different components of different endosomal membranes
describe the process of protein sorting to multivesicular bodies
- ubiquitylated cargo *Hrs protein added
- Hrs protein target receptor to ESCRT complexes , which shuttles it to invagination site where it waits for multivesicular body to turn to late endosome
what are some ways viruses and toxins enter into cells?
- translocation across endosome
- fusion with endosome
- lysis of endosome
- retrograde transport to ER
how do toxins translocate across endosome?
pH causes conformation change which allows toxins to sweep through
how does toxins fuse through with endosome
pH change causes viruses to fuse with endosome which allows them to release capsid
how does lysis of endosome occur?
bacteria poke holes in phagosome and release toxins
what does the retrograde transport of ER entail?
caveolae; toxins endocytosed to ER and use ER mechanism to get itself back out to cytoplasm
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