Topic 4C - Protein Transport via Vesicles

Question 1

what are the three types of vesicle coats

Answer 1

COPI, COPII, Clathrin

Question 2

what is the function of vesicle coats?

Answer 2

to help bend membrane and form vesicles and concentrate specific membrane proteins

Question 3

what is AP2?

Answer 3

an adaptor protein that binds to cargo receptors and membrane as part of vesicle transport with clathrin coats

Question 4

what is dynamin used for?

Answer 4

along with other associated proteins it helps get membrane close and pinch off vesicles as part of vesicle formation with clathrin

Question 5

what causes clathrin to release from vesicle?

Answer 5

PIP phosphatase!

- depletes PIP in membrane and we lose the coat when we cannot bind anymore

Question 6

what is PIPs role in clathrin coat assembly

Answer 6

when AP2 adaptor protein binds to PIP in membrane, it rearranges, exposing binding sites for cargo receptors

Question 7

what is Sar1 important for?

Answer 7

helps with COPII coat assembly

Question 8

how does COPII coat assembly work?

Answer 8

Sar1 binds a GTP, causing its helix to pop out and bind to ER membrane
Sec23-24 binds Sar1-GTP and a cargo receptor, which bind cargo
Sec13-31 also bind as an outer layer
membrane fusion event pinches off coated vesicle
when Secs activated they cause Sar1-GTP to hydrolyze –> Sar1 becomes inactive –> alpha helix pops out along with coat

Question 9

which coats does Arf1 hep assemble?

Answer 9

COPI and clathrin

Question 10

What are the steps of vesicle transport

Answer 10

tethering, docking, fusion

Question 11

how does vesicle transport work?

Answer 11

v-snare and rab-GTP bind to vesicle
tethering protein latches on to target membrane connects to Rab-GTP and pulls vesicle in
v-snare interlocks with t-snare leading to fusion (trans-snare complex), which pulls membrane close
all water is squeezed out and when membranes are very close together they fuse starting on the cytosolic side

Question 12

what drives the dissociation of snares?

Answer 12

ATP , NSF, and accessory proteins

Question 13

what does Rab help with?

Answer 13

vesicle transport –> attaches to vesicle as Rab-GTP and then a tethering protein on target membrane latches on to it pulling vesicle in

Question 14

what is homotypic fusion

Answer 14

when there are v and t snares on both membranes and they combine together to pull vesicles together

Question 15

what coats vesicles leaving the ER

Answer 15

COPII

Question 16

what coats vesicles leaving the Golgi

Answer 16

COPI

Question 17

what is special about COPI?

Answer 17

c terminal KDEL receptor binds to COPI specifically

feeds into retrieval pathway to collect runaway proteins and return them back to ER

Question 18

where do clathrin coated vesicles go?

Answer 18

transports from plasma membrane and between golgi and endosomes

Question 19

what are the main functions of the golgi

Answer 19

modify sugars

carbohydrate synthesis

Question 20

what are the two types of modifying sugars

Answer 20

complex (if enzyme can easily access)
high mannose (if hidden)

Question 21

can proteins have multiple oligosaccharides?

Answer 21

yes. they can have both types of modifying sugars too

Question 22

what processes deliver to lysosomes

Answer 22

phagocytosis
endocytosis
macropinocytosis
autophagy

Question 23

what are the functions of glycosylation

Answer 23

promotes folding
helps keep proteolytic enzymes away
regulatory roles for cell-cell recognition
sugars change from original purpose

Question 24

what are lysosomes for?

Answer 24

digestion of molecules and organelles
activated by proteolytic cleavage
have lots of transporters that are glycosylated so proteases won’t eat them

Question 25

what is endocytosis?

Answer 25

cells take up stuff from outside to be digested

enzymes are transported to these different phaes from the trans-Golgi network

Question 26

what is the pathway from the membrane to lysosome?

Answer 26

membrane –> early endosome –> late endosome –> lysosome (Digestion)

Question 27

what are the three types of pinocytosis?

Answer 27

constitutive
macropinocytosis
receptor-mediated

Question 28

characteristics of the constitutive process of pinocytosis?

Answer 28

constantly happening

Question 29

what are characteristics of macropinocytosis?

Answer 29

induced by specific signal
signal cascade activates actin –> cytoskeleton rearranges, creating a membrane shovel that scoops things we are swallowing into the cell

Question 30

receptor-mediated endocytosis

Answer 30

for importing specific extracellular macromolecules (LDL)
use clathrin coated vesicles
free cholesterol from LDL released

Question 31

three different fates for endocytosed transmembrane proteins

Answer 31

recycling
transcytosis
degradation

Question 32

how does recycling of transmembrane proteins work?

Answer 32

retrieved receptors return to same plasma membrane domain

Question 33

how does transcytosis work?

Answer 33

retrieved receptors return to different plasma membrane via recycling/ transport vesicles
big deal for asymmetrical cells

Question 34

what type of filament is phagocytosis associated with?

Answer 34

actin!
particles bind to surface and activate a signal cascade
Rho-GTPase switches on local PI kinases
- PIP stimulates actin polymerization, promoting pseudopod formation
converted to different PIP which seals off phagosome as actin is depolymerized

Question 35

what are two cases of special synaptic vesicles?

Answer 35

vesicles from Golgi that move up through nerve cell axon to fuse at synaptic cleft

partially assembled v and t snare complex for quick action when something happens of synaptic vesicle

Question 36

what is complexin?

Answer 36

helps ensure that there are no “false starts” by integrating into v and t snare
it releases from the complex when calcium signals bind to protein on synaptic vesicle

Question 37

four types of exocytosis to enlarge plasma membrane

Answer 37

cytokinesis
phagocytosis
plasma membrane repair
cellularization