Intracellular trafficking Flashcards
What is a simple definition of Vesicular transport?
Transport of protein and biomolcules (called CARGO) via transport vesicles of different shapes and sizes. These vesicles travel directionally by budding off of their primary compartment and fusing to the next one.
During membrane transport how do moleucles known there path and what pathways are normally used?
Vescular transport mediates continous exhchange of cargo between membrane enclosed compartments. Compostiion of the membrane and molecular markers on the membrane give the vescile an idea of where to go . The combination of markers gives each compartment its full moleuclar address
THey can take different pathw. Newly sythnesized cargo uses biosynthetic, things coming inside use endocytic, and retrieval is use to return items back to orgin
What are coated proteins?
Cells create coats which are segregated proteins that occur on the cytosolic side of the membrane domain. Transport vescles bud up as coated vesicles that perform 2 major functions but are discarded before vescles fuse w. target.
- Concentrates select proteins in s specialized patch for transport
- Coat molds the vesicle to form basketlike lattice that deforms the membrane and gives shape to the vesicle
What are the three types of coated vesicles
Clathrin - Vescles mediate transport from golgi appartus and Plasma Membrane *
Cop I - mediates transport from golgi cisternae
Cop II - Meduates transport from ER
What is a clathrin coated vesicle made up of?
Clathrin coated vescles are made up of Clathrin which are dived into 3 large and 3 small chains that go on to form a three legged structure called a triskelion. the trisskelions assemble into a a basketlike structure. Adapter proteins then form a second layer between cage and membrane . These layers trap various protein including receptors for _soluble cargo i_nside vescle
How does asdembly and dessembly of clatherin coated vesciles occur?
- coat proteins induce curvature in membrane
- coated buds are created
- adaper proteins bind to clathrin and membrane cargo receptors
- selective recruitment of membrane bound cargo in vescle.
- dynamin cuts vesicle (verbal mention)
- clathrin cloat lost after vescle formation
What does PI mean
Phosphoinisitides
Why is PI so important?
- Plays a major role in coat assembly, vesicle formation, and protein trafficing.
- PI’s under go rapid cycles of phsophorlaytion and desphosphorlaytion at 3’, 4’, and 5’ positions to form a multidude of variants this is called interconversion
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Interconversions are very comparmentalized, organielle and domain specfic.
- Different organelles have a specfic PI kinases and phosphatases
- Different proteins bind with highspecificity to Heads groups of particular phosphoinositides
- Control recruitment and binding of protein to specfic organelles / domains and regulates vesivles traffick
IMAGE BELOW DONT MEMORIZE BECAUSE ITS ONLY INFORMATIONAL
How is the clathrin coat removed?
A protein called dynamin assembles a ring arounf a clathrin bud
- PIP2 binding domain attaches it to membrane of vesicle
- GTPase domain regulates rate of vesticular pinching
Dynamin recruits other proteins that distort lipid biylater
- Vesicle looses coatm PIP2 degrades which weakens
- HSP 70 Chaperone protein peals off ATP to peel off coat
What is Rab Proteins?
- Directs vesicle to specfic spots on target membrane
- Activated via GTP hydrolysis
- Serves as a marker for each compartment
Inactive (GDP BOUND)
- -Rab GDP dissocation inhibitor (GDI) keeps it in inactive
- soluable and cytoslic
RAb-GTP ACTIVE
- Rab GEF keeps it in an active GTP bound form tightly bound to membrane
- active form binds to Rab efffectors (motor proteins or tethering proteins) pesent on the target membrane
What are the different types of RAB1, Rab3A, RAb5?
ER and GOLGI= RAB 1
Synaptic vesicles, secretpry vesicles = RAB3A
Early endosome, plasma membrane, and clathrin coated vesicles = RAB 5
What are SNARE proteins?
- Cataylze the fusion of vesicles with membrane
- V snares found on a vesicle membrane
- T snares found on target membrane
- V and T snares wrap around each other to form bundles
- Snape complex lock 2 membranes together
KNOW THESE SLIDES
know these slides
- RAb-GEF activates Rab GDP(with vesicle) to Rab 5 GTP
- Activates Pi 3-kinase - which phosphorlaytes Pi 3 phostphate
- recrutirs more rab Gefs
- attaches to rab effector and snares infuse vesicles
What protein dissociates SNARES?
NSF
Explain this slide
Resident proteins stay
Qualitity control with chaperones (like BiP and Calnexin)
Proteins w. Exit signal recongized by receptor on membrane
Newly synthesized proteins are packed into transport vesicle protein (COP2 w/ adapter proteins ) like clatherin ships cargo out
What are vesicular tubular clusters
Fused visicular structures occurs after budding and shedding of coat
- Homotypic - fusion of vesicles from the same compartment
- Heterotypic fusion of vesicles from different compartment
TRansport from ER to Golgi
Fusion requres Snares both v and t
shortlived
What is a retrieval pathway?
Large vesicles bud off to form smaller coated COPI vesicles
MEchanism to return proteins to ER (ER retriever signals)
KKXX sequence (lys-lys- AA-AA) at the membrane protein
KDEL on soluble proteins sequence at C terminus
KKXX signas interacts with COPI and packed into COPI coated vesicles
soluble proteins need a KDEL receptor which packages them into COPI coated vesicles
What are two parts of the golgi apparatus?
CIS golgi network (CGN)
- is a network of fused vesicular tublar tublular clusters arriving from ER proteins and lipids enter GOlgi via CGN
Trans Golgi (TGN)
- is the region that allows exit of the proteins and dlipids to next step of secretory pathway.
GOLI also plays important role in protein glycoslation
What are the two theories of transport within golgi appartus?
- Cisternal maturation model
- CIS cisternae mature into medial and then mature into the trans as its being moved its being modfified
- vesicle transport Model
- the three componets are static and that small vescicles replinish anything that move to the next transport
