Vesicular Transport Flashcards
Describe the anterograde movement of transport
ER–> golgi–> plasma membrane or lysosomes
Describe the retrograde movement of transport
plasma membrane endosome–> golgi–> golgi compartments–>ER
Describe endocytosis
plasma membrane buds, early endosome forms, golgi compartments bind and late endosome forms, lysosome
Vesicular transport involves
Cargo selection Vesicle budding Vesicle Transport Vesicle targeting Vesicle fusion and cargo delivery
Cargo selection uses a _____ ________ to bind to the cargo which in turn binds with the ______ _______ and a vesicle buds off. The adaptor proteins are shed to create a __________ _______
cargo receptor, adaptor protein, transporter vesicle
Mechanism used for vesicle transport
cytoskeletal proteins with motor proteins attached (myosin protein on actin, dyneins and kinesins on microtubules), Rab GTPs bind the motor proteins to the vesicles.
Rab proteins
GTPases that connect vesicles to motor proteins on cytoskeleton for transport. They also bind Rab effectors on the target surface to make a primary connection (highly specific). GTP form marks vesicles
SNAREs
Proteins that mediate the the fusion of the vesicle and target membranes, v and t.
The three coat proteins and which vesicles they correspond to
- Clathrin- exo and endocytotic vesicles from membrane to golgi or trans Golgi network to endosomes
- COP1- golgi to ER or golgi to other golgi compartments
- COP2- ER to golgi
ER chaperone proteins- where are they and what do they do?
in lumen of ER, they hold unfolded proteins, keeping them from getting exported in COP2 coated vesicles
Folded ER proteins need a ______ _______ with a _______ tail that will bind the COP2 protein
cargo receptor, cytoplasmic
Sar 1-GTP
a Rab-GTP like protein that allows the association of COP2 coat proteins with the ER membrane. It embeds in the ER membrane with its amphipathic helix domain (when associated with GTP).
COP 1 proteins
allow vesicles with proteins that have escaped inappropriately to be ushered back to the ER. The proteins must have the KDEL signal sequence
KDEL
ER retention signal sequence. Proteins with this can be taken up with COP1 coated vesicles and transported back to the ER (retrieval pathway)
How do you mark membrane cargo receptors for coat proteins/vesicle to recognize?
phosphorylate cytoplasmic side, have an amino acid motif, or ubiquitination
Monoubiquitination of integral membrane proteins occurs in …
early endosomes (clathrin will bind)
YxxPHI aa motif occurs in…
plasma membrane or TransGN
Describe the LDL uptake process in a cell
LDL binds to LDL receptors and clathrin associates, endocytosis occurs, and with high [acid], the LDL dissociates from the receptor. It goes into a lysosome and gets hydrolyzed–>available for use
Hyper-cholesterolemia
less cholesterol is taken up by cells, caused by LDL receptor mutation (clathrin cannot bind)
Vesicle budding is driven by ______ _______ which assemble in specific geometric shapes to create a curve.
coat proteins
Vesicle fission is assisted by …
dynamin and its associated proteins (it bring the membrane so close they fuse)
Phosphoinositides (PI3, PI4, PI4,5, etc)
hydroxyl on inositol sugar is phosphorylated on membrane- a distinguishing mark on a target organelle used to guide a vesicle and it’s specific Rab to the surface
Describe the process of vesicle recognition
PI kinase phosphrylates the specific PI, which then recruits a specific Rab GEF. This will transfer GDP off and GTP onto the incoming Rab protein of the vesicle, allowing it to embed/tether into the target membrane.
_____ promote fusion of vesicles to target
SNAREs (via scissor sort of alpha helix which is energetically favorable)
How do you break up SNAREs after fusion?
ATP, accessory proteins, and NSF cause dissociation
Botulism toxin does what to inhibit Ach transfer to muscle cells?
it cleaves SNAREs so that vesicles with ACh cannot fuse–> muscle paralysis
What is the Golgi’s main function?
it is a sorting station. The cis-golgi receives protein-filled vesicles from ER and the TGN sorts/modifies and ships to lysosomes, plasma membrane, or secretory vesicles
What are two characteristics of the Golgi?
It is made of membranous stacks very closed spaced to each other.
It is located mostly near the nucleus (perinuclear)
Enzymatic functions of the Golgi
CGN: phosphorylate oligosaccharides on on lysosomal proteins
the Cisterna: removal of Man and addition of glycans
TGN: sulfation of tyrosines and carbs
Storage granules
dense homogenous protein material formed after “distillation” of a via movement from the Golgi to the vesicle
An ________ ________ pathway will regulate some protein secretion of vesicles. Otherwise they are __________ expressed
intracellular signaling, constitutively
