Which organelles contribute to biosynthetic pathways?
- secretory vesicle
- early and late endosome
Which organelles contribute to endocytic pathways?
- late endosome to lysosome
- early endosome to late endosome
- early endosome to extracellular space
What organelles contribute to the retrieval pathway?
What does the coat of the vesicle perform?
- concentrate select proteins to a location for transport
- mold the vesicle to deform the membrane and give shape to the vesicle
- the coat is discarded before the vesicle fuses with target membranes
What mediate transport from COPI and COPII?
- from the ER to the Golgi cisternae
What mediates transport from golgi to the plasma membrane?
- clathrin-coated vesicles
What is the function of COPI?
- major role in retrieval pathway
What is the triskelion?
- clathrin subunit that had 3 large and small polypeptide chains that form a 3-legged structure
What is the function of clathrin-coated vesicles?
- transmembrane receptors bind with soluble cargo in the vesicle
What are the stages of bud formation of the clathrin coat?
- coat assembles and cargo binds to the proper receptor
- bud formation occurs when adaptor proteins bind
- vesicle continues to form, and dynamin binds to begin pinching off of the vesicle
- after vesicle is released the adaptor protein uncoats and releases a naked transport vesicle
What do phosphoinositides do in the role of protein trafficking?
help with coat assembly, vesicle formation, and protein trafficking
What is unique about phosphoinositides?
- can undergo different stages of phosphorylation and dephosphorylation to form various derivatives
- allows different organelles uniqeu set of PI kinases and phosphatases to facilitate inter-conversion
- control the recruitment and binding of proteins to specific organelles and regulate vesicle trafficking
What is a BAR domain?
- membrane bending protein
- is a coiled coil structure that dimerizes and associates with the negative PM, which induces the binding of a vesicle
What protein is required to cleave the vesicle from the PM?
- contains a PIP2 and GTPase domain
- recruits other proteins which will degrade PIP2 and allow vesicle to loose the coat
What does a Rab protein function to do?
direct vesicle to specific spot on target membrane
What does a SNARE protein funciton to do?
mediate fusion of vesicle with the membrane
What is the soluble form of Rab-GDP?
Rab-GDP bound with an inhibitor (GDI) maintains the inactive soluble form
Which form of GTP binds to the membrane?
Rab-GEFs keep Rab bound to GTP which is in the active form
What does an active Rab effector do?
facilitate the membrane tethering and fusion
What does the SNARE protein do?
catalyzes fusion of vesicles to the membrane by utilizing the v-snare on the vesicle and the t-snare on the target membrane
What components are required for membrane fusion?
- GTP-Rab to bind and tether to the target
- V-/T-SNAREs to form the stalk and budding process to complete fusion
After the two membranes fuse, what happens to the trans-SNARE complex?
- the addition of accessory proteins, NSF, and ATP produce the t-SNARE and v-SNARE components
What vesicles help transport proteins from the ER to the golgi?
COPII coated vesicles
Explain the role of BiP and calnexin?
chaperones that bind to improperly folded proteins within the ER, and label them for degradation
fusion of vesicles from the same compartment
Fusion of vesicles from different compartments
What sequence signals or ER membrane proteins to be packaged into COPI and where do they go?
- KKXX sequence
- are sent back to original organelle
What signals for soluble proteins to migrate back to their original organelle?
KDEL sequence binding with KDEL receptor
Cis golgi Network (CGN)
fused vesicular tubular clusters arriving from the ER. Allows proteins and lipids to enter golgi
Trans golgi network (TGN)
allows proteins and lipids to exit the golgi and proceed to the next step of pathway
What are the different models of how proteins are transported in the Golgi?
- cisternal maturation model
- vesicle transport model
What is the cisternal maturation model?
- vesicles from the ER combine at cis face
- the proteins migrate from CGN-> cis -> medial -> trans -> TGN and the cycle repeats for new additions
- Retrieval process moves proteins back to where they need to be
What is teh vesicle transport model of Golgi transport?