Membrane Trafficking Flashcards
1
Q
proteins are transported to organelles by while mechanisms
A
- pores
- protein translocators
- transport vesicles
2
Q
what are pores
A
selective gates that actively transport specific molecules and allow free diffusion of smaller molecules
3
Q
what do protein translocators do
A
transport proteins (typically unfolded) into organelles
4
Q
how do transport vesicles work
A
pinch off from the membrane of one compartment and then fuse with another
5
Q
what are the two methods of vesicular transport
A
- exocytosis
- endocytosis
6
Q
what is exocytosis
A
- vesicle releases contents to extracellular space
- a vesicle fuses w the plasma membrane, releasing its contents to the extracellular space
7
Q
what is endocytosis
A
- extracellular materials come into the cell via a vesicle
- extracellular materials are captured by vesicles that bus inward from the plasma membrane and are carried into the cell
8
Q
where do transport vesicles move stuff
A
- in and out of the cell
- between compartments of the cell
9
Q
what is the endomembrane system
A
a collection of organelles that are interconnected by the movement of vesicles
10
Q
vesicle budding is driven by what and why
A
- the assembly of a protein coat
- helps shape the vesicle and capture molecules for transport
11
Q
the best studied vesicles are which
A
those that have an outer coat made of the protein clathrin
12
Q
what do adaptins do
A
help select cargo receptors and cargo for movement
13
Q
what do clathrins do
A
bind to the adaptins and help shape the vesicle from the cytosolic surface
14
Q
describe the steps of vesicle formation w clathrins
A
- adaptins select cargo receptors and cargo for movement
- clathrins bind to the adaptins, to help shape the vesicle from the cytosolic surface
- dynamin assembles around the neck of the budding vesicle, then hydrolyzes their bound GTP and pinches off the vesicle
- the coat proteins (clathrin and adaptin) are removed, and the vesicle is free to fuse to its target membrane
15
Q
what is dynamin
A
a GTP-binding protein
16
Q
where are vesicles often transported and how
A
- actively transported
- along the cytoskeleton
17
Q
how does identification/ recognition happen in vesicular docking
A
- depends on GTPases called Rab proteins on the vesicle surface
- Rab proteins are recognized by corresponding tethering proteins on the cytosolic organelle surface
- SNAREs which are transmembrane proteins also help
18
Q
describe the steps of vesicular docking
A
- Rab proteins on the vesicle surface are recognized by corresponding tethering proteins on the cytosolic organelle surface
- once tethered, v-SNAREs and t-SNAREs firmly dock the transport vesicle
19
Q
what is the role of SNAREs in vesicular docking
A
- additional recognition
- v-SNAREs and t-SNAREs dock the vesicle
- also catalyze the fusion of transport vesicles to their target membrane
20
Q
describe what happens in vesicle fusion
A
- sometimes requires a stimulatory signal
- fusion complexes bring the membranes closer together so that their lipid bilayers can interact (ie displacing water from the hydrophilic surface)
21
Q
what is the major secretory pathway of the endomembrane system
A
ER to golgi to plasma membrane
22
Q
what is the major endocytic pathway of the endomembrane system
A
plasma membrane to early endosome to late endosome to lysosome
23
Q
which processes balance the amount of membrane added to or removed from the surface
A
- major secretory pathway
- major endocytic pathway
24
Q
what are common protein modifications that happen in the ER
A
- chemically modified (happens en route but starts in the ER)
- converted to glycoproteins
- transfer of oligosaccharides to new proteins
25
why does the ER transfer oligosaccharides to new proteins sometimes
- glycosylation enzymes are present exclusively in the ER lumen
- these transfer oligosaccharides to Asp residues in the newly synthesized protein
26
what bonds help with protein folding and stability
disulfide bonds
27
what helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER
chaperone proteins
28
what do chaperone proteins do
helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER
29
how do chaperones helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER
- The chaperones bind to newly synthesized or partially folded chains
- help them to fold along the most energetically favourable pathway
- requires ATP binding and hydrolysis.
30
how do isolation chamber chaperones helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER
- provides an enclosed chamber in which a newly synthesized polypeptide chain can fold without the risk of aggregating with other polypeptides in the crowded conditions of the cytoplasm.
- requires an input of energy from ATP hydrolysis
31
what happens if too many misfolded proteins accumulate
the unfolded protein response (UPR) is generated
32
what does the unfolded protein response (UPR) do
- boosts the production of proteins involved in quality control (like chaperones)
- allows a cell to adjust the size of its ER according to the load of proteins entering the secretory pathway
33
describe the structure of the golgi
- 3 20 membrane bound sacs called cisternae in the middle (cis, medial and trans)
- surrounded by cis golgi network and trans golgi network
34
describe vesicular transport through the golgi
- proteins leaving the ER move to the cis face of the golgi and fuse
- they are sorted and modified here w addition of oligosaccharides
- they head through the stack and exit on the trans face to go in diff direction
35
what are the two methods of secretion by the golgi
- constitutive pathway
- regulated pathway
36
what does the constitutive pathway do
provides a steady stream of proteins and lipids to the plasma membrane and extracellular space
37
where is the constitutive pathway active
in all eukaryotes
38
what does the regulated pathway do
large quantities of signals stores in vesicles for later release
39
where is the regulated pathway active
in cells specialized for secretion
40
what happens when proteins are ready to be secreted
- they aggregate and accumulate in high [ ] in vesicles
- there contends are finally released through docking and fusion in response to a signal
41
what is phagocytosis
- "cell eating"
- ingestion of large particles such as microbes via large vesicles called phagosomes
42
where does phagocytosis occur
in specialized phagocytic cells
43
what is pinocytosis
- "cell drinking"
- indiscriminate ingestion of fluid and molecules via small pinocytic vesicles
- vesicles fuse w endosomes and lysosomes, the material inside is degraded
44
where does pinocytosis occur
in all cells (with the aid of coat proteins)
45
how is specific material taken up in the pinocytosis
receptor-mediated endocytosis
46
describe the steps of receptor-mediated endocytosis- LDL
- cholesterol binds to LDL to be transported through the bloodstream
- LDL binds to receptors on the plasma membrane and is internalized in clathrin-coated vesicles
- vesicles lose their coat and fuse w endosomes
- endosomes are acidic, which dissociates the LDL from its receptor
- LDL is delivered to a lysosome, where it is degraded, releasing the cholesterol
- LDL receptors return to the plasma membrane to be used again
47
how do viruses exploit receptor-mediated endocytosis
- virus binds to receptors on cell surface
- receptor-mediated endocytosis of virus
- fusion of virus w cell and entry of viral genome
48
how are the golgi and endosomes alike
- golgi serves as a sorting station in the secretory pathway
- endosomes do the same in the endocytic pathway
49
what routes can be taken by receptors once they have released their cargo
- **recycling** back to plasma membrane
- **degredation** to lysosomes
- **transcytosis** to diff domains of plasma membrane
50
where does much of the material that is endocytosed end up
in lysosomes (where it is degraded)
51
how do lysosomes break down macromolecules
contains a large variety of hydrolytic enzymes which function at a low pH
52
where does material that has been digested in lysosomes go
into the cytoplasm for reuse
53
how do cells digest old organelles or groups of proteins
via autophagy
54
