Which of lambda phage, TMV, Ebola and HIV have DNA?

Only lambda phage; TMV, Ebola and HIV have RNA.

What is a retrovirus?

An RNA virus that uses reverse transcriptase to make DNA from its RNA, such as HIV.

What does reverse transcriptase do?

It makes DNA from an RNA template.

List the stages of the lytic cycle.

Attachment, entry of nucleic acid, replication and protein synthesis using host machinery, assembly, lysis.

The viral genome is incorporated into the host genome and copied with it, but no new virus particles are made.

What can end latency?

A trigger such as stress or UV light switches the virus into the lytic cycle.

Why are viruses not living cells?

They have no cell structure or metabolism and can replicate only inside a host cell.

Why do antibiotics not work against viruses?

Viruses have no cell wall or ribosomes of their own and use the host's machinery.

How must antivirals work?

By inhibiting virus replication, without harming host cells.

Why was the focus on preventing the spread of Ebola in 2014?

It is difficult to treat once infected and no vaccine or antiviral was available.

Name two measures used to control Ebola in 2014.

For example isolation of patients, contact tracing, protective clothing and safe burials.

Give two ethical arguments about untested drugs in an epidemic.

For: patients may die anyway. Against: unknown safety, consent is difficult and supply is limited.

VirusesEdexcel A-Level Biology B: Flashcards

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How are viruses classified?

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How are viruses classified?: By their structure (capsid shape, envelope) and the type of nucleic acid (DNA or RNA).
Which of lambda phage, TMV, Ebola and HIV have DNA?: Only lambda phage; TMV, Ebola and HIV have RNA.
What is a retrovirus?: An RNA virus that uses reverse transcriptase to make DNA from its RNA, such as HIV.
What does reverse transcriptase do?: It makes DNA from an RNA template.
What is a capsid?: The protein coat of a virus.
List the stages of the lytic cycle.: Attachment, entry of nucleic acid, replication and protein synthesis using host machinery, assembly, lysis.
What is latency?: The viral genome is incorporated into the host genome and copied with it, but no new virus particles are made.
What can end latency?: A trigger such as stress or UV light switches the virus into the lytic cycle.
Why are viruses not living cells?: They have no cell structure or metabolism and can replicate only inside a host cell.
Why do antibiotics not work against viruses?: Viruses have no cell wall or ribosomes of their own and use the host's machinery.
How must antivirals work?: By inhibiting virus replication, without harming host cells.
Why was the focus on preventing the spread of Ebola in 2014?: It is difficult to treat once infected and no vaccine or antiviral was available.
Name two measures used to control Ebola in 2014.: For example isolation of patients, contact tracing, protective clothing and safe burials.
Give two ethical arguments about untested drugs in an epidemic.: For: patients may die anyway. Against: unknown safety, consent is difficult and supply is limited.

Exam questions on Viruses

Human immunodeficiency virus (HIV) is an enveloped virus that infects helper T cells. Each virus particle contains two molecules of RNA and the enzyme reverse transcriptase. Zidovudine, an antiviral drug, inhibits reverse transcriptase. Penicillin, an antibiotic, has no effect on HIV.
Explain how zidovudine reduces the replication of HIV.2 marks
Lambda phage is a virus that infects the bacterium Escherichia coli. After infecting a bacterium, the phage can either destroy the cell within about an hour, releasing around 100 new phages, or have its DNA inserted into the bacterial chromosome and copied each time the bacterium divides. After many generations, exposure of the infected bacteria to ultraviolet light causes many of them to burst and release new phages.
Suggest two advantages to the virus of latency.2 marks
The 2014 outbreak of Ebola virus disease in West Africa spread rapidly through Guinea, Sierra Leone and Liberia. Ebola is an RNA virus spread by contact with the body fluids of infected people, including people who have died of the disease. At that time no licensed vaccine or antiviral drug existed. The response included isolating patients, tracing their contacts, training health workers to wear protective clothing and organising safe burials with community leaders.
Explain why control of the outbreak focused on preventing the spread of the virus rather than treating infected people.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).