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Retrovirus

Retrovirus 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 Retrovirus rather than just read about it. In short: A retrovirus is a virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backward).

Retrovirus — main illustration
Retrovirus — illustration

Key takeaways

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

Reference excerpt

A retrovirus is a virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backward). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus. Many retroviruses cause serious diseases in humans, other mammals, and birds. Retroviruses have many subfamilies in three basic groups.

Oncoretroviruses (cancer-causing retroviruses) include human T-lymphotropic virus (HTLV), causing a type of leukemia in humans, and murine leukemia viruses (MLVs) in mice. Lentiviruses (slow viruses) include HIV-1 and HIV-2, the cause of acquired immune deficiency syndrome (AIDS) in humans. Spumaviruses (foamy viruses) are benign and not linked to any disease in humans or animals. The specialized DNA-infiltration enzymes in retroviruses make them valuable research tools in molecular biology, and they have been used successfully in gene delivery systems. Evidence from endogenous retroviruses (inherited provirus DNA in animal genomes) suggests that retroviruses have been infecting vertebrates for at least 450 million years.

Structure Virions, viruses in the form of independent particles of retroviruses, consist of enveloped particles about 100 nm in diameter. The outer lipid envelope consists of glycoprotein. The virions also contain two identical single-stranded RNA molecules 7–10 kilobases in length. The two molecules are present as a dimer, formed by base pairing between complementary sequences. Interaction sites between the two RNA molecules have been identified as a "kissing stem-loop". Although virions of different retroviruses do not have the same morphology or biology, all the virion components are very similar. The main virion components are:

… excerpt ends here. Continue reading the full article.

Illustrations

Retrovirus illustration
Retrovirus: The genomic and subgenomic organization of a prototypical retrovirus. Abbreviations are explained in the file description.[18]
The genomic and subgenomic organization of a prototypical retrovirus. Abbreviations are explained in the file description.[18]
Retrovirus: A retrovirus has a membrane containing glycoproteins, which are able to bind to a receptor protein on a host cell. There are two strands of RNA within the cell that have three enzymes: protease, reverse transcriptase, and integrase (1). The first step of replication is the binding of the glycoprotein to the receptor protein (2). Once these have been bound, the cell membrane degrades, becoming part of the host cell, and the RNA strands and enzymes enter the cell (3). Within the cell, reverse transcriptase creates a complementary strand of DNA (cDNA) from the retrovirus RNA and the RNA is degraded. (4). The cDNA is then replicated, and the two strands form a weak bond and enter the nucleus (5). Once in the nucleus, the DNA is integrated into the host cell's DNA with the help of integrase (6). This cell can either stay dormant, or RNA may be synthesized from the DNA and used to create the proteins for a new retrovirus (7). Ribosome units are used to translate the mRNA of the virus into the amino acid sequences which can be made into proteins in the rough endoplasmic reticulum. This step will also make viral enzymes and capsid proteins (8). Viral RNA will be made in the nucleus. These pieces are then gathered together and are pinched off of the cell membrane as a new retrovirus (9).
A retrovirus has a membrane containing glycoproteins, which are able to bind to a receptor protein on a host cell. There are two strands of RNA within the cell that have three enzymes: protease, reverse transcriptase, and integrase (1). The first step of replication is the binding of the glycoprotein to the receptor protein (2). Once these have been bound, the cell membrane degrades, becoming part of the host cell, and the RNA strands and enzymes enter the cell (3). Within the cell, reverse transcriptase creates a complementary strand of DNA (cDNA) from the retrovirus RNA and the RNA is degraded. (4). The cDNA is then replicated, and the two strands form a weak bond and enter the nucleus (5). Once in the nucleus, the DNA is integrated into the host cell's DNA with the help of integrase (6). This cell can either stay dormant, or RNA may be synthesized from the DNA and used to create the proteins for a new retrovirus (7). Ribosome units are used to translate the mRNA of the virus into the amino acid sequences which can be made into proteins in the rough endoplasmic reticulum. This step will also make viral enzymes and capsid proteins (8). Viral RNA will be made in the nucleus. These pieces are then gathered together and are pinched off of the cell membrane as a new retrovirus (9).
Retrovirus: Phylogeny of Retroviridae
Phylogeny of Retroviridae

Worked examples

Example 1 — a first encounter with Retrovirus

Start with the simplest possible case. Write down what Retrovirus 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 Retrovirus 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 Retrovirus 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 Retrovirus

In research
Retrovirus 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 Retrovirus 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
Retrovirus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Modification of genetic information, Molecular biology, Ortervirales, so understanding it makes those chapters shorter.
In everyday life
Look for Retrovirus 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 Retrovirus in 20 minutes

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

Frequently asked questions

What is Retrovirus in simple terms?

A retrovirus is a virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the us…

Why does Retrovirus 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 Retrovirus?

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 Retrovirus.

Tags

  • Modification of genetic information
  • Molecular biology
  • Ortervirales
  • Retroviridae
  • Virotherapy

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