onion dna extraction

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leannaschultz
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Joined: Sun Mar 13, 2022 6:52 pm
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onion dna extraction

Post by leannaschultz »

My daughter and I have performed this experiment about 6 times now and cannot really get the DNA to spool. It's really difficult to measure for comparison between different onions. Just wondering if we were doing something wrong. We've followed the instructions to our best ability and then tried slight variations within the instructions (ie pipetting the ethanol onto the top vs the bottom of the tube, etc.
Thanks for any advice.
Leanna and Olivia
17eugenekim
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Re: onion dna extraction

Post by 17eugenekim »

[Note for posterity: most likely project in question, which I am referencing, is https://www.sciencebuddies.org/science- ... -onion-dna]

Hello and welcome to Science Buddies!

Sorry to hear you're having trouble with this experiment. Here's a few things you can check for:
- When heating in step 7, absolutely make sure that the temperature does not exceed 60C (140F). If it goes high enough past that, there is a risk of the DNA being destroyed/degraded.
- Make sure that you are looking for the DNA in the ethanol layer -- that will be the top layer above the rest of the solution. The DNA may float around looking like strands of mucus, or may barely be visible at all until you swish something through it and pull it out.

In addition, here's some things you can try:
- Use more ethanol. More ethanol means more of a chance for the DNA floating in solution to precipitate. It can't hurt.
- Let the ethanol sit for longer in the solution. It could just be that 2-3 minutes is not enough for the DNA to precipitate. Remember not to disturb the tube as best as possible, because that gives the DNA a chance to go back into solution. Note that keeping it cold (without freezing!) will help the precipitation process too. Solubility is lower in low temperatures.
- Add more salt. I don't know how big a difference that'll make, but it can't hurt. 1.5 g in 100 mL is about 0.25 M, and you could probably bring it up to 0.5 M (~3 g / 100 mL). The only downside I can think of is the increased potential for salt to crystallize in the final ethanol solution, so be on the lookout for white crystals or powder when you are waiting for DNA to pull out of solution. That is (likely) excess salt.
- Lastly, one other measure I can think of is using isopropanol (isopropyl alcohol). This stuff should be available at your local drugstore or pharmacy aisle. DNA is even less soluble in isopropanol than ethanol, so in theory it should be more effective at pulling DNA out of solution. Same modulation suggestions above apply to using isopropanol, but ideally you'll be needing less adjustment.

Hope that's helpful. Keep us posted on how it goes!

-Eugene
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