biology

Thyroxine 5-deiodinase

Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase rather than just read about it. In short: Thyroxine 5-deiodinase also known as type III iodothyronine deiodinase (EC number 1.21.99.3) is an enzyme that in humans is encoded by the DIO3 gene. This enzyme catalyses the following chemical reaction 3,3',5'-triiodo-L-thyronine + iodide + A + H+ ⇌ {\displaystyle \rightleftharpoons } L-thyroxine + AH2 The protein encoded by this intronless gene belongs to the iodothyronine deiodinase family.

Key takeaways

Thyroxine 5-deiodinase belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Thyroxine 5-deiodinase to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Thyroxine 5-deiodinase from memory before moving on to harder problems.

Reference excerpt

3,3',5'-triiodo-L-thyronine + iodide + A + H+ ⇌ {\displaystyle \rightleftharpoons } L-thyroxine + AH2 The protein encoded by this intronless gene belongs to the iodothyronine deiodinase family. It catalyzes the inactivation of thyroid hormone by inner ring deiodination of the prohormone thyroxine (T4) and the bioactive hormone 3,3',5-triiodothyronine (T3) to inactive metabolites, 3,3',5'-triiodothyronine (RT3) and 3,3'-diiodothyronine (T2), respectively. This enzyme is highly expressed in the pregnant uterus, placenta, fetal and neonatal tissues, suggesting that it plays an essential role in the regulation of thyroid hormone inactivation during embryological development.

Discovery The gene was mapped to chromosome 14q32 using fluorescence in situ hybridization (FISH) in 1998.

Structure This protein contains a selenocysteine (Sec) residue, which is essential for efficient enzyme activity. The selenocysteine is encoded by the UGA codon, which normally signals translation termination. The 3' UTR of Sec-containing genes have a common stem-loop structure, the sec insertion sequence (SECIS), which is necessary for the recognition of UGA as a Sec codon rather than as a stop signal.

Function

The DIO3 gene codes for type 3 iodothyronine deiodinase (D3), an enzyme that inactivates thyroid hormones and is highly expressed throughout fetal development, peaking early and decreasing towards the end of gestation. Part of the DLK1-Dio3 imprinting control region, this gene is one involved in the epigenetic process that causes a subset of genes to be regulated based on their parental origin . Such imprinted genes are required for the formation of the placenta as well as the development of cellular lineages such as those derived from the mesoderm and ectoderm. D3 is found in the pregnant uterus, placenta, and mammalian fetal tissues where it is thought to be involved in the transfer of thyroid hormone between the mother and fetus. Expression of D3 contributes to the development of the brain, skin, liver, bone, ovary, testis, intestine, and brown adipose tissue. Introductory observations of D3-deficient mice indicate growth retardation and even some neonatal death. Due to its ability to activate or inactivate thyroid hormone, Dio3 coding of D3 could be a target for therapeutic intervention in insulin-related illness such as diabetes. In addition, an abnormal amount of Dio3 related to insufficient thyroid hormone levels could be responsible for the disruption of brain development in conjunction with alcohol exposure. Many factors modify genetic imprinting of Dio3, making it a potential aid in understanding prenatal insults and their production of spectrum disorders.

References

Illustrations

Worked examples

Example 1 — a first encounter with Thyroxine 5-deiodinase

Start with the simplest possible case. Write down what Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase

In research: Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase 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: Thyroxine 5-deiodinase is common in secondary-school and first-year university syllabi. It links to neighbouring topics Developmental genes and proteins, EC 1.21.99, Genes on human chromosome 14, so understanding it makes those chapters shorter.
In everyday life: Look for Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Thyroxine 5-deiodinase in simple terms?

Thyroxine 5-deiodinase also known as type III iodothyronine deiodinase (EC number 1.21.99.3) is an enzyme that in humans is encoded by the DIO3 gene. This enzyme catalyses the following chemical reaction 3,3',5'-triiodo-L-thyronine + iodide + A + H+ ⇌ {\displaystyle \rightleftharpoons } L-thyroxine…

Why does Thyroxine 5-deiodinase 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 Thyroxine 5-deiodinase?

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 Thyroxine 5-deiodinase.