Vesicular Transmitter Release

Question 1

What triggers neurotransmitter release?

Answer 1

the calcium-mediated fusion of vesicles

Question 2

Neurotransmitter release has very high _ and _ resolution

Answer 2

Spatial and temporal
Less than 1ms

Question 3

Neurotransmitters are released in integer multiples of a _

Answer 3

Quantum

Question 4

What do quanta correspond to?

Answer 4

The contents of an individual synaptic vesicle

Question 5

What is the end plate potential?

Answer 5

The chemically induced change in electric potential of the motor end plate, the portion of the muscle-cell membrane that lies opposite the terminal of a nerve fibre at the neuromuscular junction.

Question 6

What causes the normal end plate potential?

Answer 6

The summation effects of many cholinergic vesicles being released at the same time.

Question 7

What is the evidence for vesicle recycling?

Answer 7

If they weren’t, the nerve terminals would be continually expanding

Question 8

Where are neuropeptides contained?

Answer 8

Large Dense Core Vesicles (LDCVs)

Question 9

Distribution of LDCVs

Answer 9

The vesicles are filled in the soma where neuropeptides are synthesised.
Distributed throughout the nerve terminal, appear as dark circles in electron microscope

Question 10

Where are small molecule transmitters contained?

Answer 10

Small synaptic vesicles (SSVs)

Question 11

Where are SSVs located?

Answer 11

Most are docked within the “active zone”, while the others are held within the “reserve pool”.
Docked vesicles are competent vesicles that are just waiting for depolarisation

Question 12

What causes the differences in transmitter release speed?

Answer 12

The specific response mechanism to a calcium trigger, the number of vesicles in a ready release state and the rate and efficiency of replenishment.

Question 13

What are the stages of transmitter release?

Answer 13

Docking, Priming, Fusion, Recyling

Question 14

What is docking?

Answer 14

Membrane of vesicle tightly associates with plasma membrane of the nerve terminal (otherwise vesicles are in a reserve pool)

Question 15

What is priming?

Answer 15

The creation of a competent readily releasable pool of vesicles

Question 16

What is fusion?

Answer 16

Active fusion of the primed vesicle membrane with the plasma membrane to release vesicular contents when the local calcium reaches a threshold level

Question 17

What is recycling?

Answer 17

Recycling of vesicular membrane by endocytosis to form a new vesicle for transmitter filling. (nerve terminal)

Question 18

Vesicles only operate in the _

Answer 18

Nerve terminal

Question 19

What regulates vesicle fusion?

Answer 19

The synaptic vesicle proteome

Question 20

What are synaptobrevins?

Answer 20

synaptic vesicle protein essential for vesicle fusion regulation

Question 21

What is synaptotagmin?

Answer 21

Part of the control machinery for triggering fusion event

Question 22

What are synaptophysins?

Answer 22

k, SV2s
Used as promoters for expression of something in nerve terminal as they are selective to nerve terminal machinery

Question 23

What are Rabs

Answer 23

Involved in the docking process
Rab3 is involved in both docking and priming

Question 24

What does GTP-bound Rab3 do?

Answer 24

It binds to the protein RIM on the plasma membrane to form a scaffold with Munc 13, Rabphilin and calcium channels.
This is coordinated by the lipid/calcium binding C2 domain of RIM, which ensures that docking occurs close to the site of calcium entry,
Therefore sensing of depolarisation is allowed.

Question 25

What are required for fusion events?

Answer 25

NSF - a 76kDa Homotrimer ATPase activity SNAPs for ER-Golgi and intra-Golgi transport

Question 26

What are SNAPs?

Answer 26

soluble NSF attachment proteins

Question 27

What are SNAREs?

Answer 27

SNAP receptors Membrane-anchored proteins They are what regulate fusion events

Question 28

What does VAMP do?

Answer 28

VAMP on the synaptic vesicle interacts with SNAP and NSF.

Question 29

What is the functional role of NSF and SNAPs?

Answer 29

Regulation of SNARE disassembly

Question 30

All membrane fusion secretory events involve the formation of a ___ complex assembled from SNAREs

Answer 30

Helical coiled coil complex

Question 31

Which are the SNARE proteins responsible for synaptic vesicle fusion?

Answer 31

Syntaxin 1 – presynaptic plasma membrane (integral) – tSNARE (Q) SNAP 25 – presynaptic plasma membrane (anchored) – tSNARE (Q) Synaptobrevin 2 – vesicular membrane (integral) – vSNARE (R)

Question 32

Shape of synaptic SNAREs

Answer 32

Complex of 4 parallel helices (4 helical bundle) Syntaxin and Synaptobrevin contribute one motif each and SNAP 25 contributes two motifs.

Question 33

What does MUNC 18 do?

Answer 33

It acts as a clasp to bind Syntaxin 1 and catalyse the step wise zippering of the SNAREs, pulling the membranes together.

Question 34

What drives the creation of the fusion pore?

Answer 34

The forces exerted by the SNARE complex Trans SNARE – exerts inward force. Cis-SNARE – no more force needed, single, fused membrane

Question 35

What happens before the formation of a fusion pore?

Answer 35

An intermediate hemifusion state that is not quite open or closed

Question 36

Formation of hemifused state?

Answer 36

It is rapidly triggered by Ca2+ influx and stabilised by complexin. Complexins bind SNARES with 1:1 stochiometry and arrests fusion in an hemifusion state – inner but not outer leaflets fused. Displaced by synaptotagmin

Question 37

What does synaptotagmin do?

Answer 37

It acts to put a Ca-sensitive inhibitory constraint on exocytosis. Synaptotagmin can displace complexin from SNAREs in the presence of.

Question 38

What is Synaptotagmin?

Answer 38

Am integral membrane protein on vesicles with two C-terminal C2 domains (C2A/B). Calcium and phospholipid binding domains.

Question 39

What are the three modes of endocytosis and which is the fastest?

Answer 39

Ultrafast endocytosis is fastest Kiss and run Clathrin mediated has slow refilling

Question 40

How are vesicles in the reserve pool freed of their tethers to the cytoskeleton?

Answer 40

Freed by phosphorylation of synapsin. Triggers for phosphorylation calmodulin kinase 2 and MAP kinases. Sensitive to Calcium. Triggered by change in calcium concentration.