DNA extraction practical – strawberry, banana, onion or cheek cells
BiologyBiotechnologyAges 17–18Virtual lab
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Virtual DNA extraction: mash strawberry, banana or onion tissue (or collect cheek cells), add detergent and salt, filter, add a protease such as fresh pineapple juice, then layer ice-cold ethanol and spool the white DNA at the boundary. Skip or change any step and see the spooled mass, the appearance and the purity change, with an explanation of what each step does. A results table and bar chart compare trials; built-in tasks ask for a clean, high yield, a fair test and the purpose of each step.
Lesson: Extracting DNA from plant tissue
What it shows
DNA can be extracted from fruit with kitchen chemicals. Mashing breaks cell walls, detergent dissolves the lipid membranes of the cell and the nucleus, and salt neutralises the negative charge of DNA so the strands clump. A protease, such as bromelain in fresh pineapple juice, removes proteins bound to the DNA. DNA does not dissolve in ethanol, so ice-cold ethanol layered on the filtrate brings it out as white strands that can be wound onto a rod. The yields here come from a qualitative model; real precipitate also contains RNA, polysaccharides and water.
How to use
Choose a Sample and set each step: Mashing, Detergent per 100 mL, Salt per 100 mL, Protease, Filter the mixture, Ethanol, Ethanol : filtrate and Pouring the ethanol. Press Run to watch the whole procedure, or Step to go one step at a time and read why it matters. Each finished trial adds a row to the table and a bar to the chart. Change one step at a time to make a fair test, then match each step with its purpose and press Check.
Parameters you can change
- Sample Strawberry, Banana, Onion, Cheek cells
- Mashing None, Brief, Thorough
- Detergent per 100 mL 0–20 mL
- Salt per 100 mL 0–6 g
- Protease None, Fresh pineapple juice, Canned pineapple juice, Meat tenderiser
- Filter the mixture
- Ethanol Ice-cold, Room temperature
- Ethanol : filtrate 0.5–2 ×
- Pouring the ethanol Gently down the side, Quickly
Questions to explore
- Why does no DNA appear when the detergent is left out?
- Why does canned pineapple juice not work as well as fresh juice?
- Why must the ethanol be ice-cold and poured gently down the side of the tube?
