lec 8- vesicular trafficking Flashcards
what does the Cis Golgi Network do (CGN)?
functions to sort proteins for the ER or the next golgi station
what does medial cisternae do?
it is where processing takes place in the golgi
what does the trans golgi network do (TGN)?
functions in sorting proteins either to the membrane or various intracellular destinations
what gets processed in the golgi?
the N-linked oligosaccharide that was added to nearly every protein in the ER
what is not as abundant as N-linked glycoproteins?
O-linked glycoproteins, attached to a serine or threonine hydroxyl, they are abundant in extra cellular matrix
what does the glycostation do?
-participates in sorting in the trans golgi network
-limits flexibility of protruding oligosaccharide that can prevent others from arriving to protein surface
-make glycoproteins more resistant
-serves as recognition molecule in cell-cell interactions
bottom line: gives a cell the ability to generate many chemically distinct molecules at the cell surface
what is vesicular transport model and cisternal maturation model?
-cargo is shuttled from CGN to TGN
-each cistern matures as it moves from CGN to TGN
what are the functions of coated vesicles?
-cause the membrane to curve and form a vesicle
-select the components to be carried by vesicle
what is COPII-coated vesicles?
- move materials from ER “forward” to the VTC in the ERGIC and the golgi complex
what is COPI-coated vesicles?
move materials from VTC in the ERGIC and from the Golgi complex “backward” to ER or from trans golgi to cis golgi
what is VTC and ERGIC?
VTC: vesicular tubular cluster, located in endoplasmic reticulum golgi intermedidiate compartment (ERGIC)
ERGIC: is an organelle involved in mediating traffic between ER and golgi
what do coat proteins do?
involved in endomembrane transport
what do V-snare proteins do?
it is a recognizing protein
what sequence do soluble resident ER proteins have?
KDEL (Lys-Asp-Glu-Leu), tell the golgi that this protein must remain in the ER
what happens to the KDEL protein when it gets to the golgi?
-the KDEL sequence binds to a KDEL receptor, which facilitiates COPI to take the KDEL protein back to the ER
how does vesicle budding begin?
budding begins with the recruitment of a small GTP- membrane following by binding of cytosolic coat proteins to the cytosolic domain of membrane cargo proteins
what may membrane cargo proteins be?
transmembrane proteins or receptor proteins that bind soluble proteins for transport
what do snare proteins do?
involved in the fusion of biological membranes
where are v-snare and t-snare proteins?
v-snare is in the vesicle and t-snare is in the target membrane, bringing them together to fuse
what are synaptobrevin and syntaxin?
synaptobrevin is a V-snare in the synaptic vesicle, syntaxin is a T-snare apart of the membrane of the nerve cell
how does botox paralyze muscles?
inhibits snare pairs from forming (synpatobrevin and syntaxin)
what do clatherin coated vesicles do?
clatherin coated vesicles are involved in transport from trans-golgi network to lysosomes and plasma membrane and vice versa
what is clatherin?
major protein component of clatherin coated vesicles
what is triskelion?
a clatherin molecule, each clatherin molecule consists of three large and three small polypeptide chains
how many enzymes do lysosomes have?
50 enzymes produced in the RER and can hydrolyze virtually all biological macromolecules
at what pH do lysosome enzymes function the best at in the lumen?
pH = 4.6
what do the transport proteins in the lysosome do?
carry products of macromolecule digestion to the cytosol for reuse
what is utilized for sorting and transporting lysosomial enzymes?
clatherin-coating vesicles
where are lysosomial proteins tagged and with what?
in the cis-golgi with phosphorylated mannose residues
what recognizes the tagged lysosomial proteins?
mannose-6-phosphate receptors which are bound by coat proteins in the TGN
what are lysosomial enzymes from the TGN transported in?
clatherin-coated proteins
what do the coats of clatherin coated proteins contain?
- an outer lattice composed of clatherin
- an inner shell composed of GGA adaptor proteins
- the G-protein Arf1-GTP, used to initiate membrane curvature and recruit adaptors
what does the phosphotase do to M6P (mannose-6-phosphate) residues?
removes the phosphate to prevent rebinding to M6P receptors
how are early endosomes generated?
generated by receptor mediated endocytosis
what do early endosomes fuse with and what occurs?
with late endosomes which then either transition to a lysosome or fuses with existing lysosomes (more likely)
what is autophagy?
a process of lysosomes that is a pathway that allows cytosolic proteins and organelles to be delivered to the lysosomial interior for degredation
what is a phagophore?
a double membrane structure that envelops an organelle to produce-membrane sequestering vesicle called an autophagosome and the enclosed contents are degraded
what causes lysosome storage diseases?
caused by deficiency of a lysosomal enzyme which results in accumulation of material in the lysosome
what are the symptoms of lysosomial diseases?
can be either severe or barely detectable
what causes severe lysosomial diseases?
mutations in lysosomial membrane proteins that impair transport of substances from lysosomial lumen to cytosol
what is type II glycogenosis?
a disease where glycogen accumulates in the liver, heart or skeletal muscles
what causes type II glycogenosis?
glycogen is degraded by lysosome enzymes known as alpha-1-4-glycosidase, if enzyme is not present accumulation will occur
what is Tay-Sachs disease?
an accumulation in nervous tissue of gangliosides as a result of the absence of a particular lysosomial enzyme
what is done to add the corrective lysosomial enzyme back?
enzyme replacement therapy
what is used to treat gauchers disease?
cerezyme, a modified glucocerebrosidase recognized by mannose receptors on the surface of cells for uptake
what is done to inhibit the synthesis of materials that accumulate?
substrate reduction therapy
what is used to treat both gaucher and niemann-pick disease?
Miglustat
what are the steps that occur between vesicle budding and vesicle fusion?
- movement of vesicle toward target compartment, mediated largely by microtubules and their motor proteins
- tethering vesicles to the target compartment, mediated by a diverse collection of tethering proteins
- docking vesicles to the target compartment, vesicle and target compartment membranes come into close contact via interaction between integral proteins and the two proteins
- fusion between vesicle and target membranes
what is exocytosis?
discharge of a secretory vesicle or granule after fusion with plasma membrane, triggered by Ca2+
what forms fusion pores?
interactions between vesicle and plasma membranes
what part of vesicle becomes outer and inner part of Plasma Membrane?
lumen and cytosolic part
what is endocytosis?
a process by which the cell internalizes cell-surface receptors and bound extracellular ligands
what are the two categories of endocytosis?
bulk phase and receptor mediated
what is bulk phase endocytosis?
the nonspecific uptake of extracellular fluids and may function primarily in the recycling of membrane between the cell-surface and interior compartments
what is receptor mediated endocytosis (RME)?
brings about uptake of specific ligands following their binding to receptors on the external surface of the plasma membrane
what is transcytosis?
a combination of exo and endocytosis
what is the receptors in RME concentrated in?
concentrated in coated pits at 10-20 times their level in the plasma membrane
what becomes bound to coated pits?
substances that enter the cell via clatherin mediated RME
what happens to clatherin coated regions?
invaginate into the cytoplasm and then pinch free of the cytoplasm
what do coated vesicles contain between the clatherin lattice and the surface of the vesicle?
adaptors such as AP2
what do AP2 adaptors contain?
multiple subunits that have different functions
what do AP2 adaptors do?
engage cytoplasmic tails of specific receptors to select bound cargo molecules, and bind and recruit the molecules of the overlying lattice
what forms a dynamic network of molecules in coated vesicles?
accessory proteins
what do accessory proteins do?
cargo recruitment, coat assembly, membrane bending and invagination, interaction wiht cytoskeletal components, vesicle release, and membrane uncoating
what is Dynamin and what does it self assemble into?
a G protein required for the release of clatherin coated vesicles from the membrane where it forms, self assembles into helical collar around neck of an invaginated coated pit, uses GTP to provide mechanical force
what does dynamin promote?
a GTP-mediated fission of the coated pit from the plasma membrane followed by disassembly of the dynamin ring
what are low density lipoproteins (LDL)
a complex of cholesterol and proteins, has 1500 cholesterol molecules surrounded by monolayer of p-lipids and cholesterol and a single molecule of the protein apolipoprotein B which interacts with LDL receptor
what happens to LDLs?
taken up by RME and then to lysosome to release cholesterol
what drugs lowers LDL levels?
statins which blocks HMG CoA reductase, an enzyme used in synthesis of cholesterol
how much time does it take a LDL receptor to make a round?
10 to 20 minutes
