cell bio 2b
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what are the secretory membrane system?
golgi apparatus, endoplasmic reticulum, plasma membrane
where does the secretory membrane system transport on?
microtubles and actin filaments
what are the signal sequences in secretory membrane system?
FedEx system; vesicular tubular carriers
what are the sugar systems in glycosylation?
- 2 N-acetylglucosamine
- 9 mannose
- 3 glucose
what is the calnexin cycle?
correction pathway, sends protein out of translocon when protein is incorrectly folded
what are the regulatory proteins that transport material from ER to Golgi?
Rab, Arf, Sar
what is cholesterol?
leaflet in bilayer facing extracellular space
how do we measure the movement of protein in Golgi
- transform cells with secretion protein with GFP tag (cells with a temp-sensitive mutation ER export process express FFP viral membrane protein fusion
- cells are at the restrictive temp in the start, causing accumulation of protein in ER
- when temp is lowered, trasnport can be followed
what is the function of the Golgi?
processing and sorting functions, modifications of core sugar group originated in ER, where proteins get proteolytically processed
where are sphingolipids made?
in Golgi (cis to trans)
how are the sugar groups of proteins modified in Golgi?
- cis: phosphorylation of oligosaccharides on lysosomal proteins, removal of Man
- medial: removal of Man, addition of GlcNAc
- trans: addition of GaI, addition of NANA
what are the two models that explain vesicular transport?
vesicular transport model and cis maturation model (lipids movies)
what are the proteins made in the ER?
cholesterol and phospholipid (rafts); as cells mature, they get thicker.
What is the role of lipid gradients along the secretory pathway?
transmembrane proteins sort to appropriate thickness of membrane; differences make PM less permeable and ER deformable for protein insertion; Golgi mix is perfect for sorting
which lipids move forward and which lipids have retrograde
- forward flow of cholesterol, sphingolipids and phospholipids
- some selective retrograde flow of sphingolipids and phospholipids
what is the role of coats in vesicular transport?
- formed from cytosolic proteins
- help pinch off vesicle
- select cargo for target
- coats recognize cytosolic tails of integral proteins in donor membrane
- phospholipids play role in creating domains
- motor proteins
- Arf GTPase switches
what are the protein machinery for vesicular traffic?
- specialized coats
- tethering factors
- fusion proteins
- identities of organelles
why are there different coat types?
control sorting and delivery routes
what is the role of COPII?
from ER to Golgi with help of Sar1
what is the role of COPI?
from TGN to ER Arf1
what is the role of Clathrin?
- also Arf1; from TGN to endosomes, lysosomes
- endocytosis and from endosomes to lysosomes
what are Arf GTPases?
- small GTP binding protein; binds to anchoring protein to form one of the coats
- associate with membranes via covalently bound myristol group to C-terminus
- regulate by GAP (hydrolyzes GTP/release from membrane/ inactivates) and GEFs (exchange GTP for GDP, recruits to membrane and activates)
what is the function of GTP binding protein, Sar?
- COPII associated with Sar, Sar-GTP binds ER membrane
- recruits other coat subunits of COPII
- must disassemble before fusing twith target membrane to Sar-GDP
- releases other COPII subunits
- ER to Golgi
What are the function of Sec?
- genetic secretion mutants; using coatomer to rip off vesicle from ER
- GTP to GDP releasing coatomer and releasing vessicles
what is the role of small GTP binding Arf1?
- associated with COPI
- must be hydrolyzed before coat dissambled
- golgi to ER an din between Golgi stacks
what are the components of membrane coats from transport of vesicle to and from ER?
cargo, cargo receptor, adaptin, clarthrin coat, coatomers (protein links cargo through transmembrane)
how does ER proteins know to return to ER?
KDEL sequence recognized by KDEL receptor, binds to adaptin for COI trigger assesmbly of COPI, returning it back to ER
what is the purpose of snare
transmembrane SNARE proteins in vesicles (v-SNAREs) interact specifically with target SNAREs (t-SNAREs) for forward movement of vesicles
what is SNARE regulated by?
Rabs, GTP binding protein; coats are removed prior to fusion; interact with specific Rabs
describe the Rab GTPase cycle
- switches that control interactions between transport carriers and docking complexes
- c-terminal geranylgeranyl
- also recruit motors
- large family about 70
- role of GDI
what does fusion require?
- lipid bilayers are within 1.5nm of each other
- water is removed between the two membranes
- SNARE complex disassembles after fusion
what does botox prevent?
secretion at the neuromuscular junction by destroying protein that mediates the t-SNARE/v-SNARE interactions
what are the pathways from TGN?
- Constitutive pathway to plasma membrane (partition into lipid domains richer in cholesterol and sphingolipids
- motors on MT and actin
- endosome/lysosome pathway (large and diverse group, hydrolytic enzymes in lysosome (pH)
- secretory granule pathway
where does AP3 coated vesicles go?
to late endosome
where does AP1 clathrin coated vesicles go?
to endosome, lysosome
what is the function of mannose 6 phosphate
M6P receptors put it in vesicles with AP3 trafficked to lysosome
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