Lecture 13: intracellular vesicular trafficking

Question 1

Which organelles contribute to biosynthetic pathways?

Answer 1

• ER
• Golgi
• secretory vesicle
• early and late endosome

Question 2

Which organelles contribute to endocytic pathways?

Answer 2

• late endosome to lysosome
• early endosome to late endosome
• early endosome to extracellular space

Question 3

What organelles contribute to the retrieval pathway?

Answer 3

all pathways

Question 4

What does the coat of the vesicle perform?

Answer 4

1. concentrate select proteins to a location for transport
2. mold the vesicle to deform the membrane and give shape to the vesicle
3. the coat is discarded before the vesicle fuses with target membranes

Question 5

What mediate transport from COPI and COPII?

Answer 5

• from the ER to the Golgi cisternae

Question 6

What mediates transport from golgi to the plasma membrane?

Answer 6

• clathrin-coated vesicles

Question 7

What is the function of COPI?

Answer 7

• major role in retrieval pathway

Question 8

What is the triskelion?

Answer 8

• clathrin subunit that had 3 large and small polypeptide chains that form a 3-legged structure

Question 9

What is the function of clathrin-coated vesicles?

Answer 9

• transmembrane receptors bind with soluble cargo in the vesicle

Question 10

What are the stages of bud formation of the clathrin coat?

Answer 10

1. coat assembles and cargo binds to the proper receptor
2. bud formation occurs when adaptor proteins bind
3. vesicle continues to form, and dynamin binds to begin pinching off of the vesicle
4. after vesicle is released the adaptor protein uncoats and releases a naked transport vesicle

Question 11

What do phosphoinositides do in the role of protein trafficking?

Answer 11

help with coat assembly, vesicle formation, and protein trafficking

Question 12

What is unique about phosphoinositides?

Answer 12

• can undergo different stages of phosphorylation and dephosphorylation to form various derivatives
• allows different organelles uniqeu set of PI kinases and phosphatases to facilitate inter-conversion
• control the recruitment and binding of proteins to specific organelles and regulate vesicle trafficking

Question 13

What is a BAR domain?

Answer 13

• membrane bending protein
• is a coiled coil structure that dimerizes and associates with the negative PM, which induces the binding of a vesicle

Question 14

What protein is required to cleave the vesicle from the PM?

Answer 14

• dynamin
• contains a PIP2 and GTPase domain
• recruits other proteins which will degrade PIP2 and allow vesicle to loose the coat

Question 15

What does a Rab protein function to do?

Answer 15

direct vesicle to specific spot on target membrane

Question 16

What does a SNARE protein funciton to do?

Answer 16

mediate fusion of vesicle with the membrane

Question 17

What is the soluble form of Rab-GDP?

Answer 17

Rab-GDP bound with an inhibitor (GDI) maintains the inactive soluble form

Question 18

Which form of GTP binds to the membrane?

Answer 18

Rab-GEFs keep Rab bound to GTP which is in the active form

Question 19

What does an active Rab effector do?

Answer 19

facilitate the membrane tethering and fusion

Question 20

What does the SNARE protein do?

Answer 20

catalyzes fusion of vesicles to the membrane by utilizing the v-snare on the vesicle and the t-snare on the target membrane

Question 21

What components are required for membrane fusion?

Answer 21

1. GTP-Rab to bind and tether to the target
2. V-/T-SNAREs to form the stalk and budding process to complete fusion

Question 22

After the two membranes fuse, what happens to the trans-SNARE complex?

Answer 22

1. the addition of accessory proteins, NSF, and ATP produce the t-SNARE and v-SNARE components

Question 23

What vesicles help transport proteins from the ER to the golgi?

Answer 23

COPII coated vesicles

Question 24

Explain the role of BiP and calnexin?

Answer 24

chaperones that bind to improperly folded proteins within the ER, and label them for degradation

Question 25

Homotypic fusion?

Answer 25

fusion of vesicles from the same compartment

Question 26

Heterotypic fusion

Answer 26

Fusion of vesicles from different compartments

Question 27

What sequence signals or ER membrane proteins to be packaged into COPI and where do they go?

Answer 27

1. KKXX sequence
2. are sent back to original organelle

Question 28

What signals for soluble proteins to migrate back to their original organelle?

Answer 28

KDEL sequence binding with KDEL receptor

Question 29

Cis golgi Network (CGN)

Answer 29

fused vesicular tubular clusters arriving from the ER. Allows proteins and lipids to enter golgi

Question 30

Trans golgi network (TGN)

Answer 30

allows proteins and lipids to exit the golgi and proceed to the next step of pathway

Question 31

What are the different models of how proteins are transported in the Golgi?

Answer 31

1. cisternal maturation model
2. vesicle transport model

Question 32

What is the cisternal maturation model?

Answer 32

• vesicles from the ER combine at cis face
• the proteins migrate from CGN-> cis -> medial -> trans -> TGN and the cycle repeats for new additions
• Retrieval process moves proteins back to where they need to be

Question 33

What is teh vesicle transport model of Golgi transport?

Answer 33

• proteins from ER move via vesicles to CGN, then packed into vesicles to the cis region, and so on until passed out of the golgi region