Teachers' Notes - Emerging infections: viruses that come in from the wild

DNA and Drug-resistance

This activity has two parts:

• Extracting DNA from strawberries
  
• Finding out about the genetics of HIV drug resistance

Extracting DNA from strawberries

Sequencing genetic material from hosts and from their infecting viruses is a very widespread technique in studying the biology of viral infections. Although viral sequencing is not readily available in schools, the techniques for extracting DNA from living materials are easy to do. In this example strawberries are used to give a blood-red mixture from which the DNA is extracted.  If strawberries are not available dried peas are an excellent source of DNA. You can use this procedure from the University of Utah which uses peas (http://learn.genetics.utah.edu/content/labs/extraction/howto/), and meat tenderiser which acts as an enzyme. If you can’t find meat tenderiser then you can try pineapple juice. 

Materials required

Safety glasses
Strawberries
Salt
Pestle and mortar
Tea strainers
Teaspoons
Tablespoons
Beakers (50 cm³)
Washing-up liquid
Ethanol (this needs to be ice cold) (Highly flammable, Harmful see CLEAPSS Hazcard 40A)
Test-tubes (15 cm³)
Test-tube racks

Follow the procedure on the students’ sheet.

Safety: Wear eye protection. A risk assessment must be done for the practical activity.

HIV drug resistance online activity

Introduce the students to the on-line activity explaining to them what they should do.

Instructions can be found on the students’ sheet.

The link to the online activity is at: http://www.zoo.ox.ac.uk/royalsociety350/summer_science/emerging_infections/

In this on-line activity students pick a patient identity (Patient ID) from a list and must then choose an appropriate set of medicines based upon a sequence from that patient’s virus.

They receive a nucleotide sequence and must use the triplet code to complete the amino acid sequence associated with their patient’s nucleotide sequence. When they have correctly completed this they are shown two viral sequences, one with two drug resistance mutations and one with none. They then pick a set of drugs to prescribe to the patient.

Changes in the amount of virus in the patient’s blood once they start treatment are then displayed. If the student chooses the correct drug combination the virus falls to undetectable levels. If they choose the wrong drug combination the fall in the amount of virus is only temporary.

www.avert.org/treatment.htm is an excellent online resource describing details about therapies for HIV infection.

Answers

• 1. Just a single mutation from a TAT triplet to a TAG triplet.
• 2. The 181 cys mutation gives resistance to Nevirapine.
• 3. Combination therapy is used to slow or prevent the development of drug resistance.
• 4. Zidovudine, Tenofovir and Kaletra is a drug combination that does not contain the two drugs Lamivudine and Nevirapine to which the 184 val and 181 cys mutations give resistance.

Curriculum links

Organisms and health

• 5b: Variation within species can lead to evolutionary changes, and similarities and differences between species can be measured and classified.
• 5c: The way in which organisms function are related to the genes in their cells.
• 5e: Human health is affected by a range of environmental and inherited factors, by the use and misuse of drugs and by medical treatments.

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