L5&6 Vesicular Transport I

Question 1

What systems depend on vesicular transport?

Answer 1

Biosynthetic secretory pathway

Endocytic pathway

Retrieval pathway

Question 2

General mechanism of endocytosis

Answer 2

Vesicle brought inside cell so it can’t receive signal and will be regulated

Endocytosis of extracellular molecules and membrane bound proteins initiate endocytic pathway

Used for recycling, transcytosis(transported to the opposite side of the cell), and degradation

Question 3

Where do transport vesicles originate and terminate in biosynthetic pathway?

Answer 3

Originate: ER

Terminate: plasma membrane (insoluble proteins)
Secretory vesicles to extracellular space
Endosomes
Lysosome

Question 4

What coat proteins are involved in biosynthetic secretory pathway ?

Answer 4

Clathrin
COPI
COPII

Question 5

What general types of cargo are carried in biosynthetic secretory pathway?

Answer 5

Soluble proteins

Insoluble proteins

Question 6

Where do transport vesicles of endocytic pathway originate and terminate?

Answer 6

Originate: plasma membrane

Terminate: lysosome

Question 7

What coat proteins are involved in endocytic pathway ?

Answer 7

Clathrin

Question 8

What general types of cargo are carried in endocytic pathway?

Answer 8

Membrane bound proteins

Soluble extracellular contents to be digested: proteins, lipids, nucleic acids

Question 9

Where do transport vesicles of retrieval pathway originate and terminate?

Answer 9

Originate: golgi, trans golgi, pre-secretory vesicle, early endosome, late endosome

Terminate: ER, cis golgi, golgi, plasma membrane

Question 10

What coat proteins are involved in retrieval pathway ?

Answer 10

Clathrin

COPI

Question 11

What general types of cargo are carried in retrieval pathway?

Answer 11

Abnormally processed proteins, resident ER proteins, membrane, cargo, receptors, coat protein adaptors, M6P receptor

Question 12

What’s the role of M6P?

Answer 12

Signaling factor that targets lysosomal hydrolase to lysosome

Added in the golgi

Question 13

What happens when M6P can’t be conjugated to lysosomal hydrolase?

Answer 13

Vesicles don’t get delivered to lysosome

Affect nervous system mostly

Question 14

Inclusion-Cell Disease

Answer 14

Mutation leaves cell without enzyme that conjugates M6P to lysosomal hydrolases ( in golgi)

LH secreted instead

Accumulation of molecules meant to be degraded

All organs affected

Lethal in childhood

Question 15

Clathrin facilitates vesicle formation for which pathways?

Answer 15

Proteins to early/late endosomes
From golgi BIOSYNTHETIC SECRETORY
From plasma membrane ENDOCYTIC

secretory vesicles returning from golgi
RETRIEVAL

Question 16

COPI facilitates vesicle formation for which pathways?

Answer 16

Only forms vesicles in golgi

Golgi to ER RETRIEVAL
Trans to cis golgi RETRIEVAL
vesicles containing constitutively secreted proteins BIOSYNTHETIC

Question 17

COPII facilitates vesicle formation for which pathways?

Answer 17

Only forms vesicles in ER

ER to cis golgi BIOSYNTHETIC

Question 18

Describe how plasma membrane sorting occurs in golgi

Answer 18

Through lipids rafts of cholesterol and glycosphingolipids assembled in the golgi

Question 19

Regulated secretion pathway

Answer 19

Signal (hormone or neurotransmitter) controls secretory pathway

Question 20

Constitutive secretion pathway

Answer 20

Unregulated secretory pathway

Consistently releases vesicles

Question 21

What’s the general composition of a lysosome?

Answer 21

pH 5

Must contain lysosomal hydrolase

Question 22

How are lysosomes formed?

Answer 22

When early lysosome fuses with late endosome and late endosome fuses with lysosome in endocytic pathway

pH progressively gets lower from ER to lysosome

Late endosome becomes lysosome when pH drops to 5 via H+ import

Question 23

Why is their low pH important?

Answer 23

Lysosomal hydrolases are only active at low pH

If pH isn’t low enough won’t degrade molecules

Question 24

Describe protein coat assembly

Answer 24

Cargo receptors bind donor cell
PIPs bind to membrane outside donor
Adaptor proteins bind PIPs and cargo receptors
Creates specific binding site for coat protein
Coat recruitment GTPases add another layer of regulation

Question 25

Describe coat recruitment GTPases roles in protein cost assembly

Answer 25

Hydrolyze GTP to GDP (on/off)

Inactive bound to GDP(amphipathic helix internalized)
Interact w GEFs (active GTPase)

Sar1 recruits COPII
Arf1 recruits COPI and clathrin

Question 26

Describe coat recruitment GTPases roles in protein cost disassembly

Answer 26

Shortly after vesicle formation, protein coat dissociates

Pinched off by DYNAMIN (wraps around neck of vesicle)

Coat proteins shed and are recycled

Disassembly occurs when coat recruitment GTPases hydrolyze GTP to GDP(amphipathic helix retracts out of membrane)

Coat recruitment GTPase return to cytosol

Question 27

Describe role of RabGTPases

Answer 27

When active they will bind to membrane of cargo vesicle and will interact will Rab effector to tether and dock cargo vesicle onto target membrane

Question 28

Steps in vesicle docking

Answer 28

Rab GTPase (active when bound to GTP and inserts in vesicle)

Vesicle travels along cytoskeleton

Rab GTPases interact w/ Rab GEF(specific recognition tethering protein on target membrane) and dock

RabGTPase hydrolyzes GTP (inactivation and dissociation )

Question 29

Describe vesicle fusion

Answer 29

SNARE proteins facilitate vesicle fusion- rope like proteins
V-SNARE on vesicle , t-SNARE on target

Wrap around each other, excluding water, forcing membranes together

NSF proteins hydrolyze ATP to untangle v and t SNARE proteins so they can be used again