chemistry

Tn10

Tn10 is a chemistry 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 Tn10 rather than just read about it. In short: Tn10 is a transposable element, which is a sequence of DNA that is capable of mediating its own movement from one position in the DNA of the host organism to another. There are a number of different transposition mechanisms in nature, but Tn10 uses the non-replicative cut-and-paste mechanism.

Key takeaways

Tn10 belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tn10 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tn10 from memory before moving on to harder problems.

Reference excerpt

Tn10 is a transposable element, which is a sequence of DNA that is capable of mediating its own movement from one position in the DNA of the host organism to another. There are a number of different transposition mechanisms in nature, but Tn10 uses the non-replicative cut-and-paste mechanism. The transposase protein recognizes the ends of the element and cuts it from the original locus. The protein-DNA complex then diffuses away from the donor site until random collisions brings it in contact with a new target site, where it is integrated. To accomplish this reaction the 50 kDa transposase protein must break four DNA strands to free the transposon from the donor site, and perform two strand exchange reactions to integrate the element at the target site. This leaves two strands unjoined at the target site, but the host DNA repair proteins take care of this. The target site selection is essentially random, but there is a preference for the sequence 5'-GCTNAGC-3'. The 6-9 base pairs that flank the sequence also influence selection of the insertion site. Cut-and-paste transposition does not cause an increase in the number of transposons per se: there is one copy at the start and one copy at the end. If this was the end of the matter the transposon would perish by genetic drift and the loss of copies owing to the occasional failure to achieve successful integration at the target site. However, the transposon has a mechanism to favor transposition immediately after a replication fork passes through, leaving a hemimethylated copy of Tn10 on each sister chromosome. Since transposition is favored when Tn10 is hemimethylated, the transposon on one sister chromosome can hop somewhere onto the other chromosome so that two copies of the transposon end up on one chromosome. Tn10 has a composite structure and it is composed of a pair of insertion sequence elements (IS10) flanking five genes. Only one of the IS10 elements encodes a functional transposase. Since the ends of the IS10 element contain the transposase recognition sites, Tn10 has a total of four such sites. If the transposase binds the two recognition sites flanking an IS10 element, the IS10 element undergoes transposition independently of the larger composite structure. If the transposase binds the two outermost recognition sites, the whole composite Tn10 structure undergoes transposition. Two of the five genes encoded by the central portion of Tn10, tetA and tetR, confer resistance to the antibiotic tetracycline. This activity of tetR forms the basis of the TetOFF assembly, a widely used construct in synthetic gene studies. The TetA protein is an efflux pump. It has served as a model system for such proteins and has accumulated hundreds of publications indexed in PubMed. The functions of the other three genes, jemA, jemB and jemC, are unknown but they may implicated in heavy metal resistance or oxidative stress. The Tn10/IS10 transposase is closely related to another composite transposon, Tn5/IS50, which harbors a gene for kanamycin resistance in the unique (i.e. non-repeated) central region of the transposon. The Tn10 transposon is often used in genetics to transfer and select-for genes of interest from one organism into the chromosome of another. The mechanism of Tn10 transposition has served as a model system and the archetype for the cut-and-paste mechanisms. However, the transposase is difficult to work with in vitro and the Tn5 transposase was the first to be crystallized. Tn10 was one of the great work-horses of bacterial genetics for many years during which it served as a useful tool. A commercial kit for Tn5 transposition is commercially available and is extensively used in post-genomic technologies.

References

Further reading Handford, David B.; Ellis, Michael J. (2015). "Transposons Tn10 and Tn5". In Craig, Nancy L. (ed.). Mobile DNA III. Washington, DC: ASM Press. pp. 631–645. ISBN 978-1-55581-920-0.

Worked examples

Example 1 — a first encounter with Tn10

Start with the simplest possible case. Write down what Tn10 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Tn10 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 Tn10 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 Tn10

In research: Tn10 appears in chemistry 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 Tn10 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: Tn10 is common in secondary-school and first-year university syllabi. It links to neighbouring topics DNA mobile genetic elements, so understanding it makes those chapters shorter.
In everyday life: Look for Tn10 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 Tn10 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tn10 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 Tn10 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tn10 in simple terms?

Why does Tn10 matter?

Because it connects several chemistry 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 Tn10?

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 Tn10.