Lesson 4 of 6 / Viral and bacterial genetics
HIV: RNA through a DNA stage
How can an RNA virus leave a persistent DNA copy?
I can outline retroviral inheritance using HIV.
I can explain inheritance in phage lytic/lysogenic, influenza and HIV cycles.Syllabus
Syllabus 9477, Core 2(e). Explain inheritance in phage lytic/lysogenic, influenza and HIV cycles.
About 7 min
Make a guess. You are not marked.
A drug blocks HIV reverse transcriptase. Which step of infection does it stop?
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Making DNA from the viral RNA.
Reverse transcriptase builds DNA on an RNA template. Without it, no provirus can integrate.
The key idea
HIV reverse-transcribes RNA into DNA, integrates a provirus, then uses host expression machinery to make progeny.
Explore the mechanism
Where does the DNA stage appear?
Enter a suitable cell. Receptor/co-receptor recognition and fusion deliver RNA genomes and viral enzymes. This host contains its own nucleus and ribosomes.
Brown = viral nucleic acid; purple = host nuclear region/DNA; teal circles = ribosomes. A simplified location map, not exact molecule numbers or scale. HIV's DNA intermediate is distinct from influenza's RNA-copying route.
Explanation
HIV is an enveloped retrovirus carrying RNA genomes and enzymes including reverse transcriptase. Surface glycoproteins bind appropriate receptors and co-receptors on susceptible cells, including helper T cells. Entry and uncoating deliver the viral genome and enzymes.
Reverse transcriptase uses viral RNA as a template to form DNA, ultimately producing double-stranded viral DNA. Integrase inserts this DNA into host chromosomal DNA as a provirus. The information route RNA to DNA is the distinctive retroviral step; reverse transcriptase does not synthesise viral protein.
Host transcription machinery can produce viral RNA from the integrated DNA. Some transcripts become genomes and others act as mRNA for translation by host ribosomes. Viral components assemble and bud, acquiring an envelope; viral protease processing contributes to maturation into infectious particles.
An integrated provirus can persist when little viral production occurs, helping explain long-term infection. This is a molecular inheritance mechanism rather than a statement that every infected cell behaves identically. HIV-related loss of helper T-cell function can impair coordinated immune responses.
Step by step
- 1
Trace molecule type
RNA, then DNA, then RNA and protein.
- 2
Locate persistence
Integration makes the viral sequence part of host chromosomal DNA.
- 3
Finish particle production
Assembly, budding and maturation follow expression.
Worked example
Work through the evidence
A drug blocks viral DNA integration but not reverse transcription. Which intermediate may form, and which normal next step is prevented?
One way to explain it
Viral DNA may form, but establishment of the usual integrated provirus is prevented, disrupting the normal productive/persistent pathway.
Why this answer works
- Match the blocked enzyme to its step.
- Do not claim translation directly converts RNA into DNA.
Watch out for this
A student says: "Reverse transcriptase translates RNA into a polypeptide." What is wrong with this?
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It synthesises DNA using RNA as a template. Ribosomes translate mRNA into polypeptides.
Check your understanding
Which order fits the HIV information pathway?
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RNA -> DNA -> integrated provirus -> RNA/protein production
This includes reverse transcription and integration.
Exam-style questions
Check your understanding
Which step is NOT part of the HIV replication cycle?
Show the answer
Copying viral RNA directly into new RNA genomes
HIV copies its RNA into DNA first. New RNA genomes are transcribed from the integrated provirus by host RNA polymerase.
Quick recall
How can an RNA virus leave a persistent DNA copy?