science

Nucleoside analogue

Nucleoside analogue is a science 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 Nucleoside analogue rather than just read about it. In short: Nucleoside analogues are structural analogues of a nucleoside, which normally contain a nucleobase and a sugar. Nucleotide analogues are analogues of a nucleotide, which normally has one to three phosphates linked to a nucleoside.

Key takeaways

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

Reference excerpt

Nucleoside analogues are structural analogues of a nucleoside, which normally contain a nucleobase and a sugar. Nucleotide analogues are analogues of a nucleotide, which normally has one to three phosphates linked to a nucleoside. Both types of compounds can deviate from what they mimick in a number of ways, as changes can be made to any of the constituent parts (nucleobase, sugar, phosphate). They are related to nucleic acid analogues. Nucleoside and nucleotide analogues can be used in therapeutic drugs, including a range of antiviral products used to prevent viral replication in infected cells. The most commonly used is acyclovir. Nucleotide and nucleoside analogues can also be found naturally. Examples include ddhCTP (3ʹ-deoxy-3′,4ʹdidehydro-CTP) produced by the human antiviral protein viperin and sinefungin (a S-Adenosyl methionine analogue) produced by some Streptomyces.

Function These agents can be used against hepatitis B virus, hepatitis C virus, herpes simplex, and HIV. Once they are phosphorylated, they work as antimetabolites by being similar enough to nucleotides to be incorporated into growing DNA strands; but they act as chain terminators and stop viral DNA polymerase. They are not specific to viral DNA and also affect mitochondrial DNA. Because of this they have side effects such as bone marrow suppression. There is a large family of nucleoside analogue reverse transcriptase inhibitors, because DNA production by reverse transcriptase is very different from normal human DNA replication, so it is possible to design nucleoside analogues that are preferentially incorporated by the former. Some nucleoside analogues, however, can function both as NRTIs and polymerase inhibitors for other viruses (e.g., hepatitis B). Less selective nucleoside analogues are used as chemotherapy agents to treat cancer, e.g. gemcitabine. They are also used as antiplatelet drugs to prevent the formation of blood clots, ticagrelor and cangrelor.

Resistance Resistance can develop quickly with as little as one mutation. Mutations occur in the enzymes that phosphorylate the drug and activate it: in the case of herpes simplex, resistance to acyclovir arises due to a mutation affecting the viral enzyme thymidine kinase. Since nucleoside analogues require two phosphorylations to be activated, one carried out by a viral enzyme and the other by enzymes in the host cell, mutations in viral thymidine kinase interfere with the first of these phosphorylations; in such cases the drug remains ineffective. There are, however, several different nucleoside analogue drugs and resistance to one of them is usually overcome by switching to another drug of the same kind (e.g. famciclovir, penciclovir, valaciclovir).

Examples Nucleoside analogue drugs include:

adenosine and deoxyadenosine analogues: didanosine (ddI) — HIV islatravir (ISL) — HIV vidarabine — antiviral adenosine analogues: galidesivir — Ebolavirus, remdesivir — Ebolavirus, Marburg virus, Coronavirus cytidine and deoxycytidine analogues: cytarabine — chemotherapy gemcitabine — chemotherapy azacitidine — chemotherapy emtricitabine (FTC) — HIV, hepatitis B virus lamivudine (3TC) — HIV, hepatitis B virus zalcitabine (ddC) — HIV guanosine and deoxyguanosine analogues: abacavir (ABC) — HIV aciclovir — antiviral entecavir (ETV) — hepatitis B virus ganciclovir — Cytomegalovirus lobucavir — antiviral penciclovir — Herpesvirus ribavirin — antiviral thymidine and deoxythymidine analogues: brivudine — Herpesvirus clevudine — hepatitis B virus sorivudine — Herpesvirus stavudine (d4T) — HIV telbivudine (LdT) — hepatitis B virus zidovudine (azidothymidine, AZT) — HIV deoxyuridine analogues: idoxuridine — Herpesvirus trifluridine — Herpesvirus Related drugs are nucleobase analogs, which don't include a sugar or sugar analog, and nucleotide analogues, which also include phosphate groups.

See also For nucleoside analogues in biology, see nucleic acid analogues

References

Illustrations

Worked examples

Example 1 — a first encounter with Nucleoside analogue

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

In research: Nucleoside analogue appears in science 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 Nucleoside analogue 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: Nucleoside analogue is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antiviral drugs, Nucleosides, so understanding it makes those chapters shorter.
In everyday life: Look for Nucleoside analogue 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 Nucleoside analogue in 20 minutes

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

Frequently asked questions

What is Nucleoside analogue in simple terms?

Why does Nucleoside analogue matter?

Because it connects several science 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 Nucleoside analogue?

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 Nucleoside analogue.