Intracellular Vesicular Traffic 1 Flashcards
Vesicles ________ from primary compartment and _____ with the next one
Bud off
fuse
Proteins and other biomolecules are transported via what?
Transport vesicles
Transport vesicles come in different ______ and ______:
Shapes and sizes
Small spherical or large irregular or tubular
Contents of vesicle called _____
cargo
Transport is ______
directional
___________ mediates a continuous _________ of components between various membrane enclosed compartments
Vesicular transport
exchange
_______ of the _______ and ______ on membrane surface provide cues for incoming traffic
components
membrane
molecular markers
______________ gives each compartment its full molecular address
Combination of markers
___________ return molecules to source
retrieval pathways
Cells ____ ____ into membrane domains by assembling a special ____ on cytosolic side of the membrane.
segregate proteins
coat
Transport vesicles bud off as _____ ______.
Coated vesicles
The coat performs 2 major functions:
- concentrates select proteins in a specialized patch for transport
- Coat molds the vesicle to form a basketlike lattice that deforms the membrane and give shape to the vesicle
Coat ________ before vesicle fuses with target membrane
discarded
____ and _____ mediate transport from ER to Golgi ______
COPI and COPII
Cisternae
________-________ vesicles mediate transport from Golgi apparatus and from plasma membrane
Clathrin-coated
COPI are coated vesicles of _____
Golgi
COPII are coated vesicles of ______.
ER
The major protein of clathrin-coated vesicles is _____.
clathrin
Each clathrin subunit is made of ______ and _____ polypeptide chains that form a 3-legged structure called ________
3 large
3 small
triskelion
triskelions assemble into a ___-____ structure of hexagons and pentagons that form coated pits on the _______ side of membrane
basket-like
cytosolic
______ ______ form a second layer between the cage and membrane
adaptor proteins
Adaptor proteins trap various transmembrane proteins including receptors that capture ____ _____ inside vesicle.
soluble cargo
Assembly of the coat protein molecules introduces a _____ in the membrane.
curvature
Curvature in the membrane leads too the formation of ____ ____.
coated buds
____ _____ bind clathrin and membrane-bound cargo receptors
Adaptor proteins
______ recruitment of membrane and cargo molecules in vesicle
selective
Clathrin ___ ___ after vesicle formation completed
coat lost
_________ play a major role in coat assembly, vesicle formation and protein trafficking
phosphoinositides (PI)
Phosphoinositides can undergo rapid cycles of ______ and ______ at the __,__, and__ positions to form various derivatives
phosphorylation
dephosphorylation
3’, 4’, and 5’
_______ between various phosphinositides is highly compartmentalized. It is ____ specific and ____ specific.
Interconversion
Organelle
domain
Different organelles have a unique set of __ ____ and _______ to facilitate the inter-conversions
PI kinases and phosphatases
Different proteins bind with high specificity to the ______ of particular phosphoinositidies.
Headgroups
The headgroups of PI control ____ and ____ of____ to specific organelles/domains and regulate vesicle trafficking.
recruitment and binding of proteins
What are membrane bending proteins?
BAR domains
A protein called ______ assembles a ring around a clathrin bud
dynamin
Dynamin contains a ___ ____ _____ (tethers the protein to membrane) and a _____ ______ (regulates rate of vesicle pinching)
PIP2 binding domain
GTPase domain
______ brings the 2 cytosolic sides of the membrane togehter and allows them to fuse
pinching
Dynamin recruits other proteins that _____ the____ _____ e.g., by lipid modifying enzymes that change lipid composition
distort the lipid bilayer
Vesicle looses coat, ______ is degraded which weakens the binding of adaptor proteins.
PIP2
____ ___ chaperone protein uses ATP to peel off the coat.
Hsp 70
Specificity in targeting is achieved by ____ _____ on vesicles and ______ ______ on target membrane.
surface markers
complementary receptors
Two types of proteins play an important role in vesicle targeting:
Rab and SNARE
___ _____ direct vesicle to specific spots on target membrane
Rab proteins
_____ ______ mediate fusion of vesicle with membrane
SNARE proteins
____ _____ play a central role in specificity of vesicular transport
Rab protein
Rabs are _____ ______ (~60)
monomeric GTPases
Activity of Rab is regulated by ___ _____.
GTP hydrolysis
Each Rab is associated with one or more membrane compartments of the ____ or _____ pathway.
Secretory
endocytic
Rab serves as a ____ for that compartment.
Marker
Rab cyles between ____ and _____ and regulates _______ assembly of complexes on membrane
cytosol
membrane
reversible
Rab is ____ in GDP-bound form and _____ in GTP bound form
Inactive, active
Binding to ____-____ _____ _____ keeps it in the inactive GDP-bound form. This form is _____.
Rab-GDP dissociation inhibitor (GDI)
soluble
interactions with ____-_____ keeps it in an active GTP bound form. This form is _____ bound to a membrane.
Rab-GEFs
Tightly
Active form of Rab binds to __ ____ (motor proteins or tethering proteins) present on the target membrane.
Rab effectors
Rab and Rab effectors facilitates membrane _____ and _____.
Tethering and fusion
SNARE proteins catalyze _____ of ______ with membranes
fusion of vesicles
____ different SNAREs each associated with a particular compartment
35
SNARE exist as complementary sets:
v-SNAREs (single polypeptide) found on vesicle membrane
t-SNAREs (2-3 proteins) found on target membranes
Interaction between __ and ___ forms allow them (SNAREs) to wrap around each other to form a bundle.
v and t
Resulting SNARE complexes ____ the 2 _______ together.
lock, membranes
SNAREs: Fusion may be triggered by specific ______ signals by removing _____ proteins that prevent complete fusion
extracellular, inhibitory
Dissociation of SNARE pairs involves what?
accessory proteins, NSF, and ATP
____ _____ proteins are packaged into _____ coated transport vesicles of the ER.
Newly synthesized, COPII
COPII coated transport vesicles bud off from ER ___ ____.
exit sites
Entry into vesicle is a ______ process
selective
Proteins display ___ ____ on cytosolic surface. These are recognized by receptors present on COPII coat.
exit signals
______ _____ - incompletely folded/misfolded proteins are retained in ER by binding to chaperone proteins such as ____ or ______. Such proteins are degraded.
Quality control
Bip
calnexin
After budding from ER exit sites and shedding their coat, vesicles _____ with each other.
Fuse
_______: fusion of vesicles from same compartment.
Homotypic
______: fusion of vesicles from different compartments.
Heterotypic
Fusion requires _______; both membranes contribute v- and t- _______
SNAREs, SNAREs
Fused structures are called ____ ____ _____.
Vesicular tubular clusters
Vesicular tubular clusters are _____-_____: move along microtubules to Golgi, fuse and deliver contents
Short-lived
In the retrieval pathway, large vesicles bud off to form smaller vesicles coated with _____.
COPI
The retrieval pathway is a mechanism to:
return proteins to ER
Retrieval pathway depends on __ ____ ___
ER retrieval signals
Example - ______ ____ (present in ER membrane proteins) and ____ ____ (present in soluble proteins) at C terminus
KKXX sequence,
KDEL sequence
_______ signal interacts with COPI and packaged into COPI-caoted vesicles.
KKXX
Soluble proteins need a ____ _____ which packages them into COPI-coated vesicles.
KDEL receptor
Describe the Golgi Apparatus structure
Collection of flattened, membrane-enclosed compartments (cisternae)
Each Golgi stack has 2 faces: cis or entry and trans or exit.
___ ___ ____ is a network of fused vesicular tubular clusters arriving from ER. Proteins and lipids enter Golgi via this.
Cis Golgi Network (CGN)
____ _____ ____ is the region that allows exit of proteins and lipids to next step of secretory pathway.
Trans Golgi Network (TGN)
______ plays an important role in protein glycosylation
Golgi
