Vesicle transport

On the importance of the vesicle transport system:

-proteins that function on or within the endomembrane system, the plasma membrane, or are secretory proteins are targeted to their respective final destinations via ( )

-phospholipids also move through the cell in ( )

transport vesicles

transport vesicles

moving “cargo” ( ) out of the cell from inside the cell is ( ), occurs though ( ) of vesicles from internal sources with the plasma membrane

proteins and other molecules

exocytosis

fusion

moving “cargo” into the cell from the outside is ( ), occurs through ( ) of vesicles from the plasma membrane

endocytosis

budding

phospholipids and some proteins are transported via transport vesicles, orientation remains ( ), so ( )

conserved- inside in, outside out

topology (organization/arrangement of features on each surface) is conserved 

secretory pathway ( )-molecules are transported from ( ), through ( ), to ( ) or via ( ) to ( )

red arrows

ER

Golgi

plasma membrane

endosomes

lysosomes

endocytic pathway ( )- molecules are ingested in ( ) derived from the ( ) and delivered to ( ) and then to ( ) 

green arrows 

endocytic vesicles 

plasma membrane 

early endosomes

lysosomes 

autophagy ( )- ( ) engulfed into autophagosome and go to ( )

gray arrows

cytosolic components

lysosomes

retrieval pathways ( )- endocytosed molecules are retrieved from ( ) and returned to the ( ), ( ) , or ( )

blue arrows 

endosomes 

cell surface 

Golgi

ER for reuse 

Different transport vesicles utilize different ( ) proteins.

-( ) mainly for movement from ER to ( )

-( ) mainly for movement from Golgi apparatus to ( )

coat

COPII (red)

COPI (blue)

COPII vesicle formation in ER is initiated by ( ) on ( ) by ( )- ( ) then becomes membrane bound by a ( )

guanine nucleotide exchange

Sar1 (a small G-protein)

Sar1-DEF

Sar1

amphipathic a-helix

membrane bound Sar1-GTP recruits COPII coat proteins ( ) and ( ) , ( ) specifically interacts with transport sequences on cargo proteins,

cargo receptors these specific protein-protein interactions determine which protein go into vesicles 

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Sec24

Sec24

The COPII proteins ( ) form a cage-like multimer

-forms around the vesicle as directed by ( )

-similar for COPI and clathrin coats

-not all coats form like this

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Sec 23/24

COPII-coated vesicles bud off the ER membrane with contents to be ( )

transported

receptors specifically interact with ( ), cargo proteins specifically interact with ( ) 

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receptors 

this is how cargo proteins are loaded into the vesicles, so vesicles have cargo to be transported

-only ( ) that have ( ) are loaded into COPII vesicles to leave the ER

1)cargo proteins interact with cargo receptors, which also have exit signals that

2)target them and the cargo to the correct vesicles

correctly folded proteins

exit signals

COPII-coated vesicles bud off of the ER membrane-with ( )

coat proteins ( ) after vesicle buds from donor membrane

this is the same for ( ), ( ), and ( )

contents to be transported

dissociate

COPI

COPII
clathrin coated vesicles

polymerization of actin filaments occurs near the vesicle neck, helping push the budding vesicle away from the ( )

plasma membrane 

( ) molecules assemble into a spiral around the neck of the forming bud and recruit other proteins to the bud neck, which, together with dynamin, ( ) the interacting lipid bilayers. the newly formed vesicle then pinches off from the ( )

dynamin

destabilize

membrane

what does the monomeric GTPases Rab do?

regulate intracellular vesicle traffic

These are events at target membranes-preparation to “catch” incoming vesicles

1)Rab-GEF exchange GTP to Rab (a small G-protein), causes conformation change in Rab5- (2) exposing amphiphilic a-helix and attached lipid 

-Rab proteins are held in membranes by covalently attached lipid- so they are anchored membrane proteins and a-helix

3) Rab stimulated PI kinase to tri0phosphorylate PI, which binds to Rab effector proteins 

4)Rab proteins recruit Rab effector proteins (including tethering proteins) and PI(3)P to specific areas of the target membrane for “catching” vesicles 

5)Rab proteins and phosphorinostiol phosphate PI(3)P PLUS tethering proteins and other Rab effector proteins form a “Rab membrane area” that will tether vesicles to target membranes 

( ) on vesicle specifically target and “tether” vesicle to target membranes by interacting with tethering proteins (on surface of target membrane)

Rab proteins

t-snares ( ) and v-snares ( ) to drive vesicle fusion, whereupon GTP is hydrolyzed by a GAP and Rab-GDP is released

target membranes

INTERACT (“dock” and twist)

( ) twisting forces membranes to fuse 

tSNARE/vSNARE

( ) cation channels act as neuromuscular junctions to control muscle contraction

Acetylcholine-gated

there are several ( ) proteins ( which are small G-proteins) active at several, specific locations in cells, the presence of particular Rab proteins determines ( )

Rab

specificity of vesicle transport

Golgi apparatus modifies ( ) of ( ) , nearly all ( ) in golgi are membrane proteins 

glycosylation state 

cargo proteins 

resident proteins 

( ) of proteins on serine (Ser, S), threonine (Thr, T) hydroxylated lysine (Lys, K), occurs in golgi

O-linked (on hydroxyl, OH) glycosylation

glycosylations added in ER are modified in ( )

golgi apparatus

specific glycosylation patterns provide ( ) on proteins so that they are ( ) 

specific tags 

targeted for specific functions and locations 

polysaccharides form rigid 3D structures which can be recognized by ( ) for ( )

specific molecular interactions

specific functions

( ) are formed from golgi apparatus-derived vesicles and sometimes plasma membrane derived vesicles for endocytosis or phagocytosis

lysosomes

lysosomes are proteolytic digestive ( ) 

organelles 

during acid hydrolases proteins use ( ) to digest other molecules in an acidic environment

these proteins are ( ) by a ( ) that is recognized by ( ) that are ( )

water

specifically directed to the lysosomes

“tag“ (a modified sugar attached)
receptors in the vesicles (from the Golgi)

directed to the lysosomes

lysosomes digest material from three sources:

what are they?

microorganism from outside cell (eg bacteria) by process of phagocytosis

macromolecules from outside the cell by process of endocytosis

parts of cell itself (eg mitochondria) by process of autophagy

Peroxisomes:

functions:

-( ) through oxidation reactions, producing hydrogen peroxide as a byproduct- which must be removed or it damages cells 

-( ) in the liver and kidneys ( ) that enter bloodstream ( ) 

- convert ( )

-role in ( ) in the liver ( )

breaking down fatty acids and other molecules 

detoxification reactions

detoxify toxic substances 

such as alcohol 

hydrogen peroxide, a toxic byproduct of metabolism, into water

cholesterol synthesis and bile acid production 

oxidative enzymes such as ( ) and ( ) at such high concentrations that they form crystalline structures

catalase

urate oxidase