OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.2.4 HIV as an Example of a Human Disease Caused by a Virus Exam Questions
Free OxfordAQA International A Level Biology revision for 3.2.4 HIV as an Example of a Human Disease Caused by a Virus: what you need to know, common mistakes and exam-style questions with answers. Covers the structure of HIV, its enzymes, its replication cycle in helper T cells and how drugs block it.
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About OxfordAQA International A Level Biology 3.2.4 HIV as an Example of a Human Disease Caused by a Virus
This Unit 2 topic uses HIV as the example of a disease caused by a virus. You need to describe the structure of HIV, including its RNA genome, capsid, the enzymes reverse transcriptase, integrase and protease, and the lipid envelope with glycoproteins. You also need to describe the replication cycle, from binding to CD4 receptors on helper T cells to the release of new viruses. Using information provided, you should be able to explain how drugs used to treat HIV work. It links to immunity, protein synthesis and DNA structure. Examiners often ask you to match drugs to the stage they block.
What you need to know
- Structure of HIV HIV has an RNA genome inside a protein capsid. The capsid also contains the enzymes reverse transcriptase, integrase and protease. Outside is a lipid envelope taken from the host cell membrane, with viral glycoproteins embedded in it.
- Attachment and entry HIV glycoproteins bind to CD4 receptors on helper T cells. The envelope fuses with the cell membrane and the capsid releases the RNA and enzymes into the cell.
- Reverse transcription and integration Reverse transcriptase makes a DNA copy of the viral RNA. Integrase inserts this DNA into a host chromosome.
- Making new viruses The viral DNA is transcribed into new viral RNA and mRNA, which is translated into viral proteins. Protease processes the proteins, new particles are assembled and they bud off, taking part of the host membrane as their envelope.
- Drugs and HIV Drugs can block attachment, reverse transcriptase, integrase or protease. Because HIV kills helper T cells, the immune system weakens and opportunistic infections cause AIDS.
Common mistakes in 3.2.4 HIV as an Example of a Human Disease Caused by a Virus
- Saying HIV contains DNA. HIV has an RNA genome; reverse transcriptase makes DNA from it.
- Saying HIV infects B cells. It binds to CD4 receptors on helper T cells.
- Saying antibiotics kill HIV. Antibiotics do not work on viruses; antiretroviral drugs target viral enzymes or entry.
- Describing AIDS as the virus itself. AIDS is the condition caused when helper T cell numbers fall and the immune system fails.
Try three 3.2.4 HIV as an Example of a Human Disease Caused by a Virus exam-style questions
1. Describe the role of reverse transcriptase in the replication of HIV. (2 marks)
Show the mark scheme answer
Uses viral RNA as a template; to make (single-stranded then double-stranded) DNA that can be inserted into the host chromosome.
2. A drug inhibits integrase. Explain how this would prevent HIV from replicating. (2 marks)
Show the mark scheme answer
Viral DNA cannot be inserted into the host chromosome; so it is not transcribed to make viral RNA and proteins.
3. Explain why people with HIV are more likely to develop other infections. (2 marks)
Show the mark scheme answer
HIV destroys helper T cells; so B cells and other T cells are not activated / fewer antibodies made against other pathogens.
3.2.4 HIV as an Example of a Human Disease Caused by a Virus FAQs
What does OxfordAQA International A Level Biology 3.2.4 HIV as an Example of a Human Disease Caused by a Virus cover?
It covers the structure of HIV, its enzymes, its replication cycle in helper T cells and how drugs block it.
Which unit is 3.2.4 HIV as an Example of a Human Disease Caused by a Virus examined in?
It is part of Unit 2, Biological systems and disease, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
Which HIV enzymes do I need to know?
You need reverse transcriptase, integrase and protease, and what each does in the replication cycle. Questions on drugs usually depend on knowing which enzyme each drug inhibits.
