Vesicles and secretion 1

Question 1

What is the secretory pathway?

Answer 1

A system of transporting proteins and lipids via vesicles to the plasma membrane.

Question 2

What is exocytosis?

Answer 2

Fusion of secretory vesicles with the plasma membrane.

Question 3

What are the two types of secretion?

Answer 3

Constitutive and regulated.

Question 4

How are proteins internalized from the membrane?

Answer 4

Via endocytosis into endocytic vesicles.

Question 5

Where are secreted proteins synthesized?

Answer 5

At the rough ER.

Question 6

Do vesicles retain membrane orientation?

Answer 6

Yes, exoplasmic vs cytosolic orientation is preserved.

Question 7

What is a pulse-chase experiment?

Answer 7

Labeling of cells for a short time followed by analysis at different intervals.

Question 8

What is fluorescence live imaging?

Answer 8

Using fluorescent tags to visualize protein movement in living cells.

Question 9

What did genetic analysis of yeast mutants reveal?

Answer 9

Identified sec mutants that disrupt secretion.

Question 10

What does vesicle formation require?

Answer 10

Coating of the membrane.

Question 11

What are the three main vesicle coat types?

Answer 11

COPI, COPII, and Clathrin.

Question 12

What causes membrane bending in vesicle formation?

Answer 12

Polymerization of coat proteins.

Question 13

What determines cargo inclusion in vesicles?

Answer 13

Interaction of sorting signals with coat proteins.

Question 14

What is the function of COPII vesicles?

Answer 14

Transport from ER to cis-Golgi (anterograde).

Question 15

What is the function of COPI vesicles?

Answer 15

Transport from Golgi to ER or earlier Golgi compartments (retrograde).

Question 16

What proteins initiate COPII vesicle assembly?

Answer 16

Sec12 (a GEF) activates Sar1 GTPase.

Question 17

What is Sar1’s role in vesicle formation?

Answer 17

Binds ER membrane and recruits coat proteins.

Question 18

What coat proteins assemble COPII vesicles?

Answer 18

Sec23/Sec24 followed by Sec13/Sec31.

Question 19

When does the vesicle coat disassemble?

Answer 19

After vesicle release and GTP hydrolysis by Sar1.

Question 20

Why does COPII assembly only occur at the ER?

Answer 20

Because Sec12 is only found in the ER membrane.

Question 21

What is required to pinch off COPII vesicles?

Answer 21

GTP hydrolysis by Sar1 at the vesicle neck.

Question 22

What are sorting signals?

Answer 22

Specific sequences that interact with coat proteins.

Question 23

How are soluble proteins sorted into vesicles?

Answer 23

Via cargo receptors that bind coat proteins.

Question 24

Where are sorting signals located on membrane proteins?

Answer 24

On their cytosolic regions.

Question 25

What sorting signal is common in COPII-transported membrane proteins?

Answer 25

Di-acidic motif binding to Sec24.

Question 26

How are ER-resident proteins retrieved from Golgi?

Answer 26

Via COPI vesicles using KDEL sequences.

Question 27

What does KDEL bind to?

Answer 27

KDEL receptor in the Golgi.

Question 28

Why does KDEL dissociate in the ER?

Answer 28

Because ER has a higher pH than the cis-Golgi.

Question 29

What are Rab proteins?

Answer 29

Small GTPases acting as molecular addresses on vesicles.

Question 30

What activates Rab proteins?

Answer 30

GEFs in the vesicle membrane exchange GDP for GTP.

Question 31

What do active Rab proteins bind?

Answer 31

Effector proteins on target membranes or motor proteins.

Question 32

What proteins enable vesicle-target membrane fusion?

Answer 32

SNARE proteins.

Question 33

What are v-SNARE and t-SNARE?

Answer 33

v-SNAREs are on vesicles; t-SNAREs are on target membranes.

Question 34

What forms the SNARE complex?

Answer 34

Four alpha helices formed by v- and t-SNAREs.

Question 35

What disassembles SNARE complexes?

Answer 35

ATP hydrolysis by NSF.

Question 36

Where does glycosylation begin?

Answer 36

In the ER.

Question 37

Where does further glycosylation occur?

Answer 37

In the Golgi apparatus.

Question 38

What is the cisternal maturation model?

Answer 38

Golgi compartments mature from cis to trans.

Question 39

What enables Golgi maturation?

Answer 39

Retrograde COPI vesicle transport.

Question 40

How many SNARE proteins are encoded in humans?

Answer 40

Over 40.