Neuroscience: Calcium and Synaptotagmin Interaction

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Questions and Answers

What is the primary function of the Rab3 protein in neurotransmitter release?

To target vesicles to active zones (correct)

To anchor vesicles to the cytoskeleton

To promote the recycling of vesicle membranes

To facilitate vesicle fusion with the presynaptic membrane

During vesicle mobilization, what triggers the release of vesicles from synapsin binding?

Calmodulin independent signaling

Increase in synaptic vesicle volume

Phosphorylation by PK-Ca2+/Calmodulin (correct)

Depolarization without calcium influx

What role do the SNARE proteins play in neurotransmitter release?

Transporting vesicles along actin filaments

Facilitating vesicle mobilization away from the active zone

Anchoring vesicles to synaptic membranes and preparing for fusion (correct)

Binding neurotransmitters before release

What is the significance of synaptotagmin in the process of neurotransmitter release?

It interacts with proteins to form a fusion pore upon Ca2+ binding Signup and view all the answers

How is the fusion pore formed during the neurotransmitter release process?

By the binding of synaptotagmin to membrane phospholipids in the presence of Ca2+ Signup and view all the answers

What step follows the exocytosis of vesicles in neurotransmitter release?

Endocytosis of the synaptic vesicle Signup and view all the answers

What initiates the process of vesicle mobilization in the presynaptic terminal?

Calcium influx and the subsequent phosphorylation of synapsin Signup and view all the answers

Which protein is responsible for the clathrin-mediated removal of the vesicular membrane after neurotransmitter release?

Clathrin Signup and view all the answers

What is the primary role of the Rab3 protein in the process of neurotransmitter release?

To facilitate the interaction between the vesicle and the active zone Signup and view all the answers

Which step in the neurotransmitter release process involves the interaction between the vesicle and the cytoskeleton?

Release from cytoskeleton interaction Signup and view all the answers

What is the primary function of the SNARE complex during neurotransmitter release?

To facilitate the fusion of the synaptic vesicle with the presynaptic membrane Signup and view all the answers

What role does synaptotagmin play during the process of neurotransmitter exocytosis?

It acts as a calcium sensor triggering vesicle fusion Signup and view all the answers

During the formation of a fusion pore, what primarily dictates the rate of neurotransmitter release?

The amount of Ca2+ that enters the presynaptic terminal Signup and view all the answers

What triggers the transient formation of a fusion pore during neurotransmitter release?

The influx of Ca2+ ions into the presynaptic terminal Signup and view all the answers

Which of the following best describes the all-or-nothing phenomenon of neurotransmitter release?

Once a certain threshold of calcium is reached, all vesicles release their contents Signup and view all the answers

What is the consequence of spontaneous, low-frequency quantal release in the absence of action potentials?

The occurrence of miniature postsynaptic potentials (MPPs) Signup and view all the answers

What role does Rab3 play in neurotransmitter release?

It allows anchoring to active zones through interaction with the Rim protein. Signup and view all the answers

Which protein is considered the main v-SNARE involved in vesicle mobilization?

Synaptobrevin Signup and view all the answers

How do SNARE proteins engage in the priming process during neurotransmitter release?

They undergo a zip-lock model of helical winding starting from their N-terminals. Signup and view all the answers

What triggers the fusion of the vesicle with the presynaptic membrane?

The binding of Ca2+ to synaptotagmin. Signup and view all the answers

What is the primary function of t-SNARE proteins in neurotransmitter release?

To mediate the interaction between vesicles and the active zones. Signup and view all the answers

Which of the following proteins is not classified as a t-SNARE?

Synaptobrevin Signup and view all the answers

What mechanism describes the contact interaction between SNARE proteins?

Reciprocal helical winding mechanism. Signup and view all the answers

What role does synaptotagmin play in neurotransmitter release?

It binds to calcium ions and facilitates vesicle fusion. Signup and view all the answers

Study Notes

Mechanism of Neurotransmitter Release

Initial influx of Ca2+ binds to synaptotagmin, inducing a conformational change that facilitates interaction with SNARE proteins.
SNARE proteins (v-SNARE and t-SNARE) bring synaptic vesicles close to the presynaptic membrane, preparing for neurotransmitter release.

Vesicular Stages in Release Process

Mobilization: Phosphorylation of synapsin releases vesicles bound to cytoskeleton (actin filaments), allowing movement towards active zones.
Traffic: Vesicles are targeted to active zones through G proteins, including Rab3 (vesicular) and Rim (membrane).
Docking & Priming: Vesicles are anchored at active zones via SNARE complex, consisting of synaptobrevin (v-SNARE), syntaxin, and SNAP-25 (t-SNARE).

Fusion Process

Fusion: Ca2+ binding to synaptotagmin facilitates vesicle fusion with presynaptic membrane, creating a fusion pore.
This process results in neurotransmitter release through exocytosis, driven by the significant increase in intracellular Ca2+ during action potential (AP).

Neurotransmitter Characteristics

Synaptic vesicles serve as storage organelles for neurotransmitter quanta; release is all-or-nothing and depends on Ca2+ influx.
Each vesicle represents one quantum of neurotransmitter; for example, one vesicle contains approximately 5,000 molecules of acetylcholine (ACh).

Action Potential Influence

In absence of AP, a low-frequency spontaneous quantal release occurs (~1 quantum/sec), while AP increases the release rate by over 100,000 times, leading to ~150 quanta/msec.

Exocytosis and Fusion Pore Dynamics

Exocytosis is facilitated by a transient fusion pore formed between vesicular and presynaptic membranes.
Ca2+ promotes the opening and dilation of fusion pores for effective neurotransmitter release.

Summary of Release Steps

Steps involved in neurotransmitter release include:
- Release from cytoskeleton interaction
- Targeting and anchoring to active zones of the plasma membrane
- Preparation for fusion (priming)
- Fusion with the presynaptic membrane

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Description

This quiz explores the role of calcium ions (Ca2+) in neuronal signaling, particularly how Ca2+ interacts with synaptotagmin and the SNARE proteins during synaptic transmission. Test your understanding of the mechanisms underlying neurotransmitter release and synaptic functioning in the nervous system.