Lecture 13 - Endomembranes & Vesicles Flashcards
what are the functions of vesicles protein coatings?
- curve the membrane to form the vesicle
- select the components to be carried in the vesicle
def: vesicle coating, acts as a scaffolding cage around the vesicle
outer layer
def: vesicle coating, acts as an adaptor between the outer layer and the lipid bilayer/cargo
inner layer
def: move materials from the ER “forward” to the ERGIC and Golgi complex
COPII coated vesicles
def: move materials from the ERGIC and Golgi “backward” to ER or from the trans Golgi to the cis Golgi cisternae
COPI coated vesicles
def: move materials from the plasma membrane “backwards”, and the TGN to the endoscopes/lysosomes/plant vacuoles
Clathrin-coated vesicles
in a COPII coated vesicle, what is budding initiated by?
the recruitment of small GGTP binding proteins (GTPases) = SAR1-GDP to a patch of donor membrane
what gives COPII vesicles their curvature?
Sec23 and Sec24 dimers, since they have curved conformation
def: not only curving protein, but also acts as an adaptor protein, associating with ER export signals recruiting proteins to the forming vesicle
Sec24
def: integral membrane protein crucial for the fusion of the vesicle to the correct target membrane
v-SNAREs
in COPII what forms the cage like outer layer?
Sec13 and Sec 31
for COPII vesicles, the outer layer is a relatively simple _____, with each vertex forming from the convergence of ____ ______ ____ dimers
lattice, four Sec13 and Sec31 dimers
what happens to the protein coat while in transit of COPII and why
it disassembles and release its contents back into the cytosol so the v-SNAREs are accessible and the vesicle can target the proper membrane
what chemical process mediates the disassembly of the protein coat of the vesicle?
hydrolysis of GTP, producing SAR1-GDP
what mediates the movement of vesicles while reaching their targets?
microtubules
the initial contact between a vesicle and the target membrane involves _________ proteins
tethering
what are the 2 groups of tethers?
- rod shaped fibrous proteins that form long bridges
- multi-protein complexes that hold two membranes close together
def: regulates membrane specificity and is responsible for most of membrane vesicle/target specificity, group of GTPases
Rab GTPases
how does Rab-GTP allow docking to occur?
- recruits the cytosolic tether proteins to the membrane surface
- recruits motor proteins to the vesicle to facilitate transport
SNARE proteins _____ _______ between vesicles and target membranes
mediate fusions
def: sorting and targeting of vesicles involves two families of SNARE proteins
SNARE hypothesis
def: SNARE proteins found on vesicles
v-SNARE
def: SNARE proteins found on target membranes
t-SNARE
T or F: v- and t-SNAREs are not complementary molecules to each other
False, they are complementary molecules
v- and t-SNARE __________ intertwine, pulling the membranes together
alpha helices
in vitro, the v-SNARE–t-SNARE interaction is strong enough to cause _______ ______, but in vivo, a rise in ____ _________ is thought initiate fusion
membrane fusion, Ca2+ concentration
T or F: After fusion, the v- and t-SNARE are still tightly associated, and are now in the same membrane
true
how do v- and t-SNAREs dissociate after membrane fusion has occurred?
- require NSF and SNAPs to pry apart the SNAREs, using energy from ATP hydrolysis
where do v-SNAREs go after the vesicle transport has occurred?
they are shuttled back to the previous compartment to repeat this process
what is the main difference between how COPI- coated vesicles are formed compared to COPII
they use different coat and adaptor proteins
def: aka a secretory pathway, vesicle contents are released to the exterior, vesicle membranes fuses with the plasma membrane
exocytosis
def: imports extracellular molecules by forming vesicles with the plasma membrane, in steady state with exocytosis
endocytosis