Lecture 13: Synaptic Release and Presynaptic Proteins

Question 1

A mammalian NMJ synapse has approximately how many active zones?

Answer 1

10-100, compared to the 300 in the frog. Many hippocampal and neocortical synapses consist of a single active zone

Question 2

An active zone consists of:

Answer 2

Presynaptic region containing vesicles, the synaptic cleft, and a post synaptic density

Question 3

True or false:
Type I (excitatory) synapses have a thinner PSD than type II (inhibitory)

Answer 3

False. Type I excitatory synapses have a thicker PSD than type II inhibitory synapses

Question 4

Each active zone releases how many vesicles?

Answer 4

One or not at all. In the hippocampus, different circuits have probabilities between 10% and 90% of releasing vesicles.

Question 5

Number of molecules per vesicle:

Answer 5

~1000-5000

Question 6

Mossy fibre synapse of the hippocampus

Answer 6

Contains 30-40 active zones.
More current flows into the dendrite.
The synapses are located close to the cell body (less current leakage)

Question 7

All membrane fusion events require:

Answer 7

1. Formation of a SNARE complex - pulls the two membrane structures together
2. An SM protein e.g. Munc 18 - initiates phospholipid mixing by bending the opposite membranes towards each other

Question 8

Describe the four SNARE protein alpha helices.

Answer 8

Vesicle docking requires the fusion of 4 SNARE protein alpha helices.
One supplied by the vesicle (Synaptobrevin/VAMP)
Three supplied by the plasma membrane at the synaptic terminal - Two helices per SNAP-25 protein, One helix per syntaxin protein

Question 9

Function of Munc18

Answer 9

Promote bending of phospholipid bilayer via steric hindrance. This is essential for fusion.

Question 10

Function of Synapsin

Answer 10

Synapsin tethers “resting” vesicles to actin

Phosphorylation of synapsin allows forward movement of vesicle

Question 11

Function of Rab 3

Answer 11

Rab 3 targets vesicles to the docking site (by binding to RIM protein, which is bound to VACCs)

Question 12

Function of Rab 5

Answer 12

Rab 5 is important for re-uptake after exocytosis

Question 13

Normal cycle of vesicle recycling

Answer 13

SNARE complex is disassembled. Vesicle returns to Recycling Pool

Question 14

The rapid cycle of vesicle recycling

Answer 14

SNARE complex remains intact, and vesicle remains docked in RRP

Question 15

The slow cycle of vesicle recycling

Answer 15

SNARE disassembly occurs, vesicle joins endosome compartment then enters the reserve pool