exam 3 vesicular transport Flashcards
what occurs via vesicular transport
movement of proteins between the ER, most membranous organelles, and the cell surface
what do proteins have to undergo before using vesicular transport to get into ER
undergo transmembrane transport
what are proteins transported by in vesicular transport
transported by vesicles, which bud off of one organelle and fuse with another and deliver contents that way
what are proteins guided by
specific coat and targeting proteins
what do retrograde pathways do
they are reverse pathways that allow the return of “escaped” proteins to original organelles and the recycling of targeting proteins
what serves as roadways for vesicular transport
cytoskeleton
why do proteins never have to cross a membrane from one side to the other using vesicular transport
vesicular transport keeps topological similarities
what does vesicular sorting depend on
the assembly of a special protein coat formed at specific locations along a given donor compartment
what do coat proteins do
deform membrane to start vesicular formation and initiate targeting to next compartment
what are the 3 main classes of coat proteins
COPI, COPII, clathrin
what is COPII used in
coating vesicles that bud off of ER and go to golgi
what is COPI used for
vesicles that bud off of golgi and move internally or go to ER and plasma membrane
what is clathrin used for
transport between cell surface, golgi, and endosomes
what represents the initial step in vesicle formation
coat proteins
what do transport vesicles bud off as
as coated vesicles that have a distinctive cage of proteins covering their cytosolic surface
what closes off membrane into spherical vesicle
a forced curvature of membrane due to coat proteins - before the vesicle fuses with a target membrane, the coat is discarded to allow the two cytosolic membrane surfaces to interact directly and fuse
what marks organelles and membrane domains
phospholipids containing inositol head groups
how do coat proteins know where they are
lipid concentrations are different in different domains
what/where can inositol get phosphorylated by
inositol can get phosphorylated at various locations by different lipid kinases
what can different phosphorylations be recognized by
other proteins, which can then tag membranes to identify them - kinases are selectively associated with different membranes
what can phosphoinositides recruit
various proteins that possess lipid binding domains (which only recognize a specific type of PI)
how can binding be regulated
by phosphorylating or dephosphorylating polar head groups
what do adapter proteins bind to
membrane proteins or membrane to recruit coat proteins (often bind to cargo receptors)
what controls coat assembly
coat recruitment GTPases
what does assembly of coat proteins involve
binding of GTP form
what does disassembly of coat proteins involve
GTP is hydrolyzed to GDP
which of cytosol and ER membrane bound forms of coat proteins are inactive and active
GDP is in cytosol = inactive
GTP is ER membrane-bound = active
what allows for specificity in vesicle targeting
surface markers that identify vesicles according to their origin and type of cargo
what is recognition of donor vesicles by acceptor membranes controlled by
SNAREs and Rabs
what do Rabs do
type of GTPase that works together with other proteins to regulate the initial docking and tethering of the vesicle to the target membrane
how do Rabs transfer to SNAREs
Rabs release protein when it is hydrolyzed to GDP - this transfers to SNAREs
what do SNAREs do
provide specificity and catalyze vesicular fusion of the target membrane
what are v-SNAREs and t-SNAREs
v = vesicle
t = target membrane
make a very tight interaction and the force of this drives fusion events between membranes - separated later using ATP hydrolysis
how do Rab and SNAREs work together
Rab tethering protein catches vesicle, SNAREs force fusion between two membranes
how does cargo recruitment work
- membrane proteins have exit signals in the cytosolic tails that are recognized by coat proteins
- soluble proteins bind to cargo receptors that have exit signals in their cytosolic tails
what happens after transport vesicles bud off of ER
they fuse together to form intermediate compartments called vesicular tubular clusters
what do vesicular tubular clusters do
- travel towards the cis golgi via motor proteins on microtubule tracks
- generate coated vesicles going back to the ER (COPI coat) - retrograde transport
what happens with ER retrieval signals
- membrane ER resident proteins retrieve signals in their cytosolic tails, recognized by COPI coat proteins
- soluble ER resident proteins retrieve signals within their structure and bind to receptors
what are the two models for how cargo travels through the golgi
static model and dynamic model
what is the static model
golgi stacks (cisterae) remain the same throughout - vesicles travel between them, moving proteins
what is the dynamic model
golgi stacks (cisternae) move upward, changing their protperties slightly as they migrate
how do enzymes get returned
through vesicular transport in retrograde directions
how do proteins leaving golgi get to plasma membrane
vesicles carrying them fuse with the plasma membrane via exocytosis
what are the two basic pathways of secretion
constitutive secretory pathways and regulated secretory pathway
what happens with constitutive secretory pathway
- once you leave golgi, directed to plasma membrane which you fuse with
- no additional signal required
what happens with the regulated secretory pathway
secreted components are concentrated into secretory vesicle which moves to plasma membrane. it requires an external signal to trigger fusion of vesicle with plasma membrane
what are clathrin-coated vesicles used for
transport between plasma membrane, endosomal system, and golgi
what is the structure of clathrin
composed of three copies each of heavy and light chains; arranged in a triskelion
what does clathrin interact with
cargo receptors and other markers to drive vesicle formation, then clathrin coat is lost
what is dynamin
a GTPase that is a cytoplsasmic proteins which control the pinching-off of clathrin-coated vesiclse
how does dynamin work
- wraps around the stem of the budding vesicle
- brings inner leaflet membranes of vesicles together
- fusion of these membranes severs the vesicle from the donor compartment
- GTP hydrolysis regulates rate of vesicle pinching off
what are the characteristics of lysosomal enzyme cargo
soluble, carry a unique marker - mannose 6-phosphate (M6P) groups
what happens when lysosomal enzyme cargo is recognized by M6P receptor in golgi network
it’s packaged into clathrin-coated vesicles for delivery to lysosomes
what are endosomes
intermediate organelles in vesicular transport pathways between plasma membrane, lysosomes, and golgi
what are the three classes of endosomes
early, late recycling
what are early endosomes
develop from endocytosis
what are late endosomes
mature from early endosomes to become more like lysosome compartments
what are recycling endosomes
compartment that after some cargo has delivered to endosomes, compartments can go back to plasma membrane
what do endosomes eventually mature into
lysosomes by becoming increasingly acidic because of addition of proton pumps
what do proton pumps do
move protons from cytosol and concentrate them inside compartment to become more acidic
what happens in exocytosis
vesicle fuses with plasma membrane and releases cargo
what happens in endocytosis
vesicle comes in from outside and pinches off
what does low pH activate enzymes to do
to be able to degrade biological molecules
what are multivesicular bodies
vesicles with vesicles in them - characterizes maturation of late endosomes
what happens to membrane proteins and lipids as vesicle cargo
they’re removed from the plasma membrane and some will be recycled back to surface, some will be degraded
what happens to soluble proteins as vesicle cargo
they’re from extracellular space and are carried into the lumen to be degraded
what are the common components targeted during exocytosis
cell surface receptors and the ligands that bind them
what is phagocytosis
cellular eating - the ingestion of large particles, such as microorganisms or dead cells via vesicles called phagosomes
what is pinocytosis
cellular drinking - the ingestion of fluids and solutes by vesicles called pinocytic vesicles, including receptor-mediated endocytosis
what do cells do constantly in terms of endocytosis
pinocytosis - doesn’t require a trigger - it’s how cells get fluids in cell and sample nutrients
how does cholesterol get into cells
via receptor-mediated endocytosis
what receptors generally get recycled to the cell surface
receptors that involve the transport of nutrients
what receptors generally get degraded
receptors involved in signaling events because that turns off signaling to reset the cell
what is transcytosis
moving from one side of a polarized epithelium to another
