biology

MT-ND3

MT-ND3 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 MT-ND3 rather than just read about it. In short: MT-ND3 is a gene of the mitochondrial genome coding for the NADH dehydrogenase 3 (ND3) protein. The ND3 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the largest of the five complexes of the electron transport chain.

Key takeaways

MT-ND3 belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MT-ND3 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MT-ND3 from memory before moving on to harder problems.

Reference excerpt

MT-ND3 is a gene of the mitochondrial genome coding for the NADH dehydrogenase 3 (ND3) protein. The ND3 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the largest of the five complexes of the electron transport chain. Variants of MT-ND3 are associated with Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), Leigh's syndrome (LS) and Leber's hereditary optic neuropathy (LHON).

Structure

General features MT-ND3 is located in human mitochondrial DNA from base pair 10,059 to 10,404. The MT-ND3 gene produces a 13 kDa protein composed of 115 amino acids. MT-ND3 is one of seven mitochondrial genes encoding subunits of the enzyme NADH dehydrogenase (ubiquinone), together with MT-ND1, MT-ND2, MT-ND4, MT-ND4L, MT-ND5, and MT-ND6. Also known as Complex I, this enzyme is the largest of the respiratory complexes. The structure is L-shaped with a long, hydrophobic transmembrane domain and a hydrophilic domain for the peripheral arm that includes all the known redox centres and the NADH binding site. The MT-ND3 product and the rest of the mitochondrially encoded subunits are the most hydrophobic of the subunits of Complex I and form the core of the transmembrane region.

Untranslated extra nucleotide In the MT-ND3 gene from many species of birds and turtles there is an extra nucleotide that is not translated to protein. Translational frameshifting or RNA editing are alternative explanations for the maintenance of the functionality of the ND3 reading frame in birds possessing the one-nucleotide insertion. This extra nucleotide feature suggests that turtles might be related to Archosauria, as evidenced by molecular phylogeny studies. The absence of the extra nucleotide in crocodilians and some birds and turtles might also indicate that the corresponding taxa have lost this feature.

Function The MT-ND3 product is a subunit of the respiratory chain Complex I that is believed to belong to the minimal assembly of core proteins required to catalyze NADH dehydrogenation and electron transfer to ubiquinone (coenzyme Q10). Initially, NADH binds to Complex I and transfers two electrons to the isoalloxazine ring of the flavin mononucleotide (FMN) prosthetic arm to form FMNH2. The electrons are transferred through a series of iron-sulfur (Fe-S) clusters in the prosthetic arm and finally to coenzyme Q10 (CoQ), which is reduced to ubiquinol (CoQH2). The flow of electrons changes the redox state of the protein, resulting in a conformational change and pK shift of the ionizable side chain, which pumps four hydrogen ions out of the mitochondrial matrix.

Clinical significance Pathogenic variants of the mitochondrial gene MT-ND3 are known to cause mtDNA-associated Leigh syndrome, as are variants of MT-ATP6, MT-TL1, MT-TK, MT-TW, MT-TV, MT-ND1, MT-ND2, MT-ND4, MT-ND5, MT-ND6 and MT-CO3. Abnormalities in mitochondrial energy generation result in neurodegenerative disorders like Leigh syndrome, which is characterized by an onset of symptoms between 12 months and three years of age. The symptoms frequently present themselves following a viral infection and include movement disorders and peripheral neuropathy, as well as hypotonia, spasticity and cerebellar ataxia. Roughly half of affected patients die of respiratory or cardiac failure by the age of three. Leigh syndrome is a maternally inherited disorder and its diagnosis is established through genetic testing of the aforementioned mitochondrial genes, including MT-ND3. These complex I genes have been associated with a variety of neurodegenerative disorders, including Leber's hereditary optic neuropathy (LHON), mitochondrial encephalomyopathy with stroke-like episodes (MELAS) and the previously mentioned Leigh syndrome.

Interactions MT-ND3 has been shown to have 5 binary protein-protein interactions including 2 co-complex interactions. MT-ND3 appears to interact with APP and NDUFA9.

References

Illustrations

Worked examples

Example 1 — a first encounter with MT-ND3

Start with the simplest possible case. Write down what MT-ND3 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 MT-ND3 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 MT-ND3 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 MT-ND3

In research: MT-ND3 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 MT-ND3 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: MT-ND3 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human mitochondrial genes, Proteins, so understanding it makes those chapters shorter.
In everyday life: Look for MT-ND3 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 MT-ND3 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MT-ND3 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 MT-ND3 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MT-ND3 in simple terms?

Why does MT-ND3 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 MT-ND3?

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 MT-ND3.