Zaidi Lecture 9/26 Trafficking Flashcards
How are proteins and other biomolecules transported throughout the cell?
transport vesicles
How do the proteins and biomolecules get from one compartment to another?
Bud off and fuse with the next one
What are the contents of a vesicle called?
cargo
In vesicular trafficking, is transport directional or bidirectional, and why?
directional; because all of the proteins know where they are destined to go
What are the two aspects of the cell that help to provide cues for the incoming traffic?
The composition of the membrane and the molecular markers on the membrane surface
What returns the molecules to its original source?
Retrieval pathways
What are the 2 functions of the coat on the outside of the vesicles?
- concentrates are able to select proteins
2. coat is able to mold the vesicle and give it a shape
True or False: The coat on the vesicle remains surrounding the vesicle all the way through fusion to the target cell
False
Where does COPI transport from?
Golgi
Where does COPII transport from?
ER
Where does the Clathrin-coated vesicles mediate transport from?
Golgi apparatus and the plasma membrane
Describe the structure of the clathrin subunit
there are 3 large and 3 small polypeptide chans that for a triskelion
Describe what triskelions assemble into
A basket like structure of hexagons and pentagons that form coated puts
Describe the assembly and disassembly of the clathrin coat
- The adaptor proteins (which help to trap ish inside of the vesicle) bind to the receptors on the cell, and cause a curvature of the membrane
- The membrane continues to bubble out
- Membrane bending and fission proteins come to the cell and “snip” the vesicle loose
- the adaptor proteins leave and the transport vesicle is naked heyooooo
What is one of the reasons why phosphoinositides play a major role in the coat assembly?
They are able to undergo phosphorylation and dephosphorylation to form a variety of derivatives
How do organelles “code” for one membrane domain or another in regards to transport vesicles?
They have their own sets of PI kinases and phosphates that allow for interconversion of the phosphoinositides to make the vesicle more organelle specific
Headgroups are specific
What does the head group of a PI serve as?
The signature, it is what the kinases and the recognition particles on the organelle look for
What is the function of the BAR domains?
Membrane bending proteins
Describe the removal of the clathrin coat.
- protein called dynamin assembles a ring around it
- pinching allows the 2 cystolic sides of the membrane to come together and fuse
- dynamin recruits other proteins that distort the lipid bilayer by changing the composition of the lipids
- vesicles loses its coat
- HSP70 protein uses ATP to peel off the coat
What are the two domains that are present within dynamin and what are their functions?
PIP2 binding domain- tethers the protein to the membrane
GTPase domain-regulates the rate of the vesicle pinching
What are the two major proteins that are involved in vesicle targeting?
SNARE and Rab
Define Rab proteins
direct the vesicle to spots on the membrane: active and inactive forms when attached to GTP/GDP like the Ran
Define SNARE proteins
mediate the fusion of the vesicle with the membrane
catalyze the interaction of the vesicles with the membrane
What is the soluble form of the Rab protein?
When the Rab is bound to the Rab-GDP dissociation inhibitor (GDI), it is kept in the inactive form
