My banana DNA extraction disaster

This morning I had a frustrating experiment which, thanks to my amazing luck, failed! Well, it wasn't so much my luck as it was my poor planning.

I followed the steps outlined by "Ask A Biologist" to complete a DNA extraction using a banana. Materials required were a ripe banana, hot water, salt, dish soap, a plastic bag, very cold isopropyl (rubbing) alcohol, a coffee filter, a narrow glass, and a wooden stirrer. My first few problems arose when I realised I, in fact, did not have rubbing alcohol, and so substituted vodka! I would later learn this was my first of many mistakes - more details on that later.

A beautiful photo of my materials all gathered together.

Unfortunately for you all, I'm no biologist; I haven't done a lick of biology in the last two years, until today! So I will try my best to explain to you all the purpose of each of these materials.

• The banana is present to, obviously, have the DNA extracted from it. The method specified a ripe banana, and I immediately thought, "Why, what difference does it make?" From skimming this interesting essay, I found that ripened fruit produces many more DNA strands than under-ripe and over-ripe fruit. Under-ripe fruit doesn't produce sufficient juice after mashing, whereas over-ripe fruit produces a lot of juice, but a lot of the DNA has decomposed by this point.
• Dish soap is an anionic surfactant (essentially a negatively charged compound which loves water), which causes cells to lyse (pop). The cell membrane (outer part of a cell) is made of lipids (fat), which dish soap is effective at breaking down, meaning the membrane breaks down and the outsides spill out.
• Salt allows the DNA to clump together, making it more visible. DNA naturally has a negative charge, which is why it's so soluble in water, but this means that the positive sodium ions in salt are very attracted to it (think how opposing magnet poles are attracted to each other). This neutralises the charge of the DNA, meaning it more easily becomes a precipitate (solid) in alcohol.
• Ice-cold isopropyl alcohol is used because although DNA is soluble in water, it's insoluble in ice-cold isopropyl alcohol, meaning it can be viewed in a separate layer from the water,

I followed the steps outlined on the website to a tee, with only a few minor accidents.

As you can see, I began by beautifully mashing my banana and making my salt water, only spilling half of it onto the kitchen counter rather than all of it.

They were then mixed together by yours truly, like a true lab professional. Before adding the dish soap, and certainly not spilling it all over the place, despite having the scooper hovering inside the bag.

a photo of the aftermath of
adding the banana solution and
dish soap

My next step was the treacherous goal of adding this concoction to a narrow glass through filter paper.

The first time failed (unsurprisingly). I hadn't thought about securing the filter paper to the glass, and it immediately fell through. Thankfully, this was swiftly fixed ("Phew," you all say in unison), as I quickly went upstairs and used a hair bobble of a colour I would never consider wearing - perfect for a DNA experiment. 

before

after

(No one knows how much I struggled to put these

  even somewhat side-by-side)

These next steps severely tested my patience - waiting for the banana solution to fill even an inch of the glass was truly boring (I definitely didn't use this time to get dressed for the day). I also will not mention the first attempt to do this, where I tried to mash the mush up, and instead put a hole in the coffee filter, causing it all to fall into the glass. I also will not mention I spilt half of it when trying to pour the remaining contents from the bag into the glass.

What you all don't know can't hurt you.

After waiting the painstakingly long time for the solution to separate, it was time for the exciting stage - adding the vodka. Despite my excitement, I made sure to tilt the glass and slowly add it. Nothing. I waited a bit, tried a bit slower. Nothing. After all my pain and suffering (20 minutes of my time), it had failed. Unfortunately, I have no evidence for this failure as I poured the solution down the sink in anger. It was 9:00am and I, for some reason, was as tired as a mother of newborn triplets, which only amplified my annoyance.

My genius thought that, since I didn't have rubbing alcohol, I could use vodka because they're both alcohols - I was very wrong about that. What I didn't know was that vodka is only about 40% alcohol, with the rest being water. Since DNA is soluble in water, this meant that the DNA would just dissolve in it, and they also wouldn't form separate layers. What I also hadn't considered - and what should have been painfully obvious as a former A-Level chemistry student - is that the vodka is mostly water! From what I've seen, the vodka I used contains ethanol, which, if you need reassurance, means it does not contain isopropyl alcohol (or at least not at the concentration required for this experiment). This means that if I had wanted to use ethanol, I would have had to use pure ethanol, rather than the highly dilute vodka ethanol.

Not only was my poor planning a failure, but by the time I added my water to the mushed banana, it had cooled down to a colder temperature, when it was meant to be quite warm. Allegedly, 'science' backs the fact that warm water helps dish soap break down fatty-lipid membranes, but who believes in that 'science' rubbish? Certainly not me...

Despite all my jokes throughout this post, I did find this valuable. I now understand the importance of not slacking and just substituting materials you don't currently have, as it can affect the whole reaction. I'm sure that the next time I repeat this experiment, I will have splurged in buying isopropyl alcohol (rubbing alcohol), I really am investing big money into this blog.