Friday, 7 August 2020

What is DNA?

 What is DNA? 

What is DNA?





 Deoxyribonucleic acid or DNA for short is the molecule that carries the genetic information in all living organisms In terms of structure, DNA's a polymer that's made of four sub-units known simply as A (adenine), C (cytosine), T (thymine), and G (guanine) Each of these sub-units has three main components: a unique nitrogenous base, a phosphate group, and a sugar They connect together through their phosphate groups to form these long polymer chains, which are the basis of DNA The order of the sub-units is extremely important and it's how the genetic information is stored It gets a little more complicated though because DNA isn't just one chain, it's actually two and they're held together by interactions between the nitrogenous bases This interaction is known as hydrogen bonding Where A likes to pair with T and C with G This hydrogen bonding along with various other intermolecular forces twists the DNA into its characteristic ladder-like structure known as a double helix In this double stranded system, the cell only reads the information from one strand and the other is kept as a backup For example, if a mutation occurs and let's say a C is swapped for an A, the cell can recognize and fix this because the A wouldn't properly pair with the G Or maybe if some sort of damage occurs to a large section of one strand the cell can simply cut it out and rebuild it based on the other one This is not how DNA looks in the cell though. It's associated with a whole ton of proteins that pack it together into a super small volume It progressively gets packed tighter and tighter until we eventually get something called a chromosome which is the smallest DNA base structure that you can see under a typical microscope Each chromosome contains a different set of genes and the number of chromosomes varies widely among plants and animals For humans, we have 23 pairs of chromosomes, so 46 in total. What might be interesting is that the number of chromosomes doesn't have any thing really to do with the sophistication of the organism For example, a typical potato has 48 so two more than a human What i think is really cool is that it's actually possible to isolate DNA from pretty much any living thing For this video though I've decided to get it from strawberries because it's one of the easiest sources Also at the end, once I've isolated the pure DNA, I'm gonna try it out because I'm really interested to know what it tastes like Anyways in terms of supplies I'll of course need some strawberries but I'll also be using some dish soap non-Iodized salt And 99% isopropyl alcohol Before I get started with the main process, there are a couple things I need to do first The isopropyl alcohol will be used later on but it needs to be ice cold so i measure out about 200 milliliters and then I put it in the freezer I also need to prepare a soapy salt solution to do this i mix a hundred and eighty milliliters of water 20 milliliters of dish Soap and about a teaspoon of salt Ideally, the soap that's used is both uncoloured and unscented but unfortunately I wasn't able to find this What I ended up using was this red strawberry scented soap because i figured both the color and the smell would be masked by the strawberries The table salt should also be non-iodized but it will work if only regular iodized salt is available   What we're doing here is making a so called "extraction solution" that we'll be using to get the DNA out of the cells For now, it's going to be temporarily placed on the side But when I use it in a few minutes i'll explain exactly how it works Okay with that other stuff out of the way, we can get started with the actual procedure! I counted out 10 moderately sized strawberries and then I shoved them all into a seal-able bag One thing I should mention is that this preparation really doesn't need gloves and I'm not really sure why i'm wearing them for it (silly Nile) Anyway, with all the strawberries in the bag, it's time to squish them By doing this, I'm exposing as many of the strawberry cells as possible and I'm also structurally damaging them This crushing step is really easy to do with strawberries and it's a major reason why I'm using them It's common to extract DNA from other things like chicken liver or peas, but they don't fall apart nearly as easily and you often need to use a blender After a few minutes, things should be adequately broken up so it's time to add the soapy extraction solution from before Then I mix it around and try to break up any pieces that I might have missed It really doesn't look like much as going on here but it's actually the most important step in the extraction, which is getting the DNA out of the cells For plant cells, which strawberries are made of, this is the general anatomy There's a whole bunch of stuff here that's not relevant and I really want you to just focus on the three main things: the cell wall, the cell membrane, and the nuclear membrane The cell wall is a rigid sugar layer that's usually made of cellulose and the other membranes are made of things called phospholipids 
What is DNA?


is stored in the nucleus, so to get to it we need to destroy all three of these barriers The first to go was the cell wall, which was broken when I pulverized the strawberries This exposes the cell membrane, which as i mentioned a second ago is made of phospholipids The phospholipids organize themselves into a bilayer like this: where the polar heads are on the outside and the non-polar tails are shielded on the inside Soap itself is very similar to the phospholipids where it has a polar head but it only has one non-polar tail The structural difference is small, but , in water, it causes soap to form spherical structures called micelles instead of these bilayers Even though they form these very different and distinct structures, they're still similar enough that they want to interact with each other When the soap is added, it starts plucking phospholipids and proteins from the cell membrane and incorporating it into its own micelles. Also, to some degree, the soap molecules will insert themselves into the membrane This ultimately leads to severe damage of the lipid bilayer and it makes it structurally unstable With further squishing the membrane bursts open and the contents of the cell are spilled out This releases the nuclear membrane which is the last thing to get through and it's just like the cell membrane The soap messes with the lipid bilayer causing it to burst and the DNA is released Although the cells are just spitting out DNA we don't actually see it here because it stays dissolved in the water As I mentioned in the intro though the DNA is tightly packed and associated with a lot of different proteins Many of the proteins have positive charges which interact with the negative charges of the phosphates in DNA This is why we add the sodium chloride. The sodium ion can come in and displace a lot of these proteins For me i felt this salt was good enough but a lot of People also include some protein enzymes to further free up the DNA After a few minutes of squishing I now need to filter off all the solid strawberry junk This is done in two steps. First through a strainer to get rid of the really large pieces and then through a coffee filter to get rid of the smaller stuff This part is really slow so It requires some patience Also the filter tends to get jammed up so i needed to replace It at least three or four times Once everything passes through though we are ready to isolate the DNA So to do this, I get the ice-cold isopropyl alcohol from earlier and I dump it all in Very quickly there's a bunch of This white stringy stuff floating to the top and this is the DNA However there are probably some proteins that precipitate out as well I try to pull some out with tweezers but It doesn't really work I also try scooping It out with a spoon but that had problems as well So instead i just mix things up and I waited for all the DNA to float to the top After several minutes it was much more compact and clumped up so It was a lot easier to scoop out I transferred it to a coffee filter and i waited for most of the liquid to drain through Then It was thoroughly washed several times with cold isopropyl alcohol Afterwards I was left with this soft and gooey DNA but now i need to wait for the alcohol to evaporate I put It on a piece of paper and It took about a day or so for all the alcohol to disappear By the time it fully dried it had turned slightly brown and it was quite hard I imagined the brown color is just due to oxidation of some impurities that were extracted along with the DNA However I'm not entirely sure Just to show you how hard it is, I dropped it on a watch glass and you can hear the clinking sound that it makes The mass of the DNA here is about 250 milligrams and I got this from 10 strawberries so each one contains about 25 milligrams Because the DNA is made of lots of long fibers it's surprisingly strong It was a lot easier just to use my fingers and tear It up like a piece of paper but it still wasn't the easiest thing to do I decided to try chopping up some of the pieces again and i was honestly impressed with just how much force it took anyway now I think it's time to try eating it Okay so here i have the DNA that I extracted and it's this very small amount in the bag I'm just gonna take out small little piece now give it a taste Ah! [Spits] It has a There's a really terrible, terrible texture At first it's just hard but after it just kind of gets slimy and it just tastes kind of salty. Doesn't have anything else besides that I think the salt is either from salt i didn't wash off after the extraction or it's actually from the sodium ions that are associated with the DNA in either case the flavor isn't too strong but it's just vaguely salty slimy and gross As usual, a big thanks goes out to all my supporters on Patreon Everyone who supports me can see my videos at least 24 Hours before I post it to YouTube and they can also directly message me All supporters with five dollars or more will get their name at the end of the video like you see here 

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