biology

Synapsin 2

Synapsin 2 is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Synapsin 2 rather than just read about it. In short: Synapsin II is the collective name for synapsin IIa and synapsin IIb, two nearly identical phosphoproteins in the synapsin family that in humans are encoded by the SYN2 gene. Synapsins associate as endogenous substrates to the surface of synaptic vesicles and act as key modulators in neurotransmitter release across the presynaptic membrane of axonal neurons in the nervous system.

Key takeaways

Synapsin 2 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Synapsin 2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Synapsin 2 from memory before moving on to harder problems.

Reference excerpt

Synapsin II is the collective name for synapsin IIa and synapsin IIb, two nearly identical phosphoproteins in the synapsin family that in humans are encoded by the SYN2 gene. Synapsins associate as endogenous substrates to the surface of synaptic vesicles and act as key modulators in neurotransmitter release across the presynaptic membrane of axonal neurons in the nervous system.

Gene Alternative splicing of the SYN2 gene results in two transcripts. The TIMP4 gene is located within an intron of this gene and is transcribed in the opposite direction.

Protein Synapsin II is a member of the synapsin family. Synapsins encode neuronal phosphoproteins which associate with the cytoplasmic surface of synaptic vesicles. Family members are characterized by common protein domains, and they are implicated in synaptogenesis and the modulation of neurotransmitter release, suggesting a potential role in several neuropsychiatric diseases. This member of the synapsin family encodes a neuron-specific phosphoprotein that selectively binds to small synaptic vesicles in the presynaptic nerve terminal. Synapsin II the collective name for two proteins, synapsin IIa and synapsin IIb, with synapsin IIa being the larger of the two isoforms. Their apparent molecular weights are 74,000 and 55,000 Da, per SDS gel electrophoresis. Synapsin II along with synapsin I comprise approximately 9% of the proteins in highly purified samples of synaptic vesicles.

Structure Synapsin II shares common domains within its amino acid sequence with other phosphoproteins in the synapsin family. Sharing the same N-terminal, synapsin II diverges from synapsin I in its C-terminal domains. It is much shorter than synapsin I and is missing most of the elongated domains seen in synapsin I. Roughly 70% of the amino acid residues are common between the two synapsins, which share common phosphorylation sites in the overlapping regions based on the homologous domains. Domain A of this neural protein contains phosphorylation sites for cAMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase I, and domain B has two mitogen-activated protein kinase phosphorylation sites. At its B domain, between amino acids 43 and 121, synapsin II binds to a protein component in the cytosolic surface membrane of synaptic vesicles, organelles in neurons which carry neurotransmitters.

Function Synapsin II regulates synaptic function of neurons in the central and peripheral nervous system. Synapsin IIa is the only synapsin isoform of the six synapsin isoforms (synapsin I-III each with isoforms A and B), which has been shown to significantly reverse synaptic depression and have a restorative effect on the density of synaptic vesicles within synapsinless neurons. Because of its restorative effect, synapsin IIa is believed to play a fundamental role in synaptic vesicle mobilization and reserve pool regulation in presynaptic nerve terminals. Lack of synapsins altogether in neurons, leads to behavioral alterations as well as epileptic-type seizures. The lack affects nervous signal transduction across excitatory and inhibitory synapses of neurons differently and is believed to be synapse-specific. Initial signal transduction appears to be unaffected by the lack of synapsins, but repeated stimulation of cultured synapsinless hippocampal neurons subsequently showed depressed responses at the excitatory synapse. At the inhibitory synapse, base signal transduction is reduced in neurons lacking pre-existing synapsins, but the reduced level of transduction is less affected by progressive stimulation. However, the restoration of synapsin IIa to neurons without pre-existing synapsins, can partially recover presumably lost signal transduction and slow the depression of synaptic response with progressive stimulation. Its isoform synapsin IIb may have a similar but weaker effect. Through fluorescence and staining, it has been demonstrated that synapsin IIa increases the number and density of glutamatergic synaptic vesicles in the nerve terminal of neural axons. The recovery of nervous signal transduction is attributed to the increase in density of synaptic vesicles, which carry neurotransmitters to the synaptic cleft, and the amount of synaptic vesicles in the reserve pool in the presence of synapsin IIa. In turn, this is thought to increase the number of vesicles available for mobilization from the reserve pool to the ready-release pool. The reserve pool is the pool of synaptic vesicles which reside in the nerve terminal away from the presynaptic membrane of the axon, but are not in the ready to release or ready-release pool. Those vesicles in the ready-release pool reside very close to the presynaptic membrane and are primed to release neurotransmitters for nervous signal transduction.

Interactions The synapsin II protein has been shown to interact with SYN1.

Clinical significance Mutations in the SYN2 gene may be associated with abnormal presynaptic function and schizophrenia.

References

Illustrations

Worked examples

Example 1 — a first encounter with Synapsin 2

Start with the simplest possible case. Write down what Synapsin 2 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Synapsin 2 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Synapsin 2 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Synapsin 2

In research: Synapsin 2 appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Synapsin 2 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Synapsin 2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 3, Human proteins, Molecular neuroscience, so understanding it makes those chapters shorter.
In everyday life: Look for Synapsin 2 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Synapsin 2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Synapsin 2 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Synapsin 2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Synapsin 2 in simple terms?

Why does Synapsin 2 matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Synapsin 2?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Synapsin 2.