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We speak student!

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Molecular Genetics

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DNA Extraction

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A la Shmoop

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Okay, we're back with you in the land of biology

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and we're gonna talk about DNA extraction

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with Dr. Ruth Tennen here who is a guru on the subject.

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So, Dr. Ruth, why would anyone want to

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extract DNA in the first place?

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What does that do for us?

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Like, when I go to Vermont,

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I understand why I want to extract maple syrup -

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because it tastes good.

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[ pop ] [ mm-mm ]

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Why would anyone want to extract DNA?

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A similar idea. So, maple syrup doesn't do you any good

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- when it's in the tree. - Right.

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Just like if you wanna study the DNA,

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you should get it out of the cell.

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So, tons of reasons you might wanna do this.

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Let's say you wanna do some forensic testing.

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So you found DNA at a crime scene

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and you want -- you have a suspect, you gotta take his DNA.

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You have to extract his or her DNA out of their cells and test it.

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Same thing with genetic testing. You can't really sequence

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or figure out what the sequence of DNA is

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while it's in someone's cell.

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So you have to burst open the cell, take out the DNA,

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so you can study it and sequence it.

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Wow, that's really cool.

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So the obvious question is -

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How do you extract DNA?

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Can we buy a kit that does that for home use?

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Well, you can buy a kit if you're in the lab.

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Home use is actually super easy. Just use the kitchen ingredients.

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There's just a few steps. So the first thing you have to do

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is break open the cell.

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And you can do that by grinding them.

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You can often add detergent.

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So, soap is something that will break up the [ indistinct ].

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- Wait, go back. Grinding cells? - Yeah.

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I'm thinking about the maize flour thing, so you take --

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The mortar and pestle, yeah. That'll do it.

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Wow. So, wait a sec. We've got dried blood

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from the, I don't know, the guy who got shot.

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And you, like, stick it in a bowl

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and it dries and you pound it?

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So, probably, if they were doing it in a lab,

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they would not use that.

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- They have, like, a little tube that'll do everything. - [ laughs ] Yeah, right. Understood.

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But if you wanna take your cheek cells,

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you basically could just slough them off using Gatorade

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and then spit them in a tube

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and they would kind of --

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that sort of mechanical chewing would separate them a little bit.

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Wow. That's gross and really cool at the same time.

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- It's pretty awesome. - Yeah. Okay, keep going.

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Sure, so, you've got your cells that you got out of your organism

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- however you did. - [ laughs ]

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And then you would add detergent and salt,

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which basically breaks open the cell membrane

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and the nuclear membrane.

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So that'll kind of release the DNA.

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The problem at that point is that the DNA

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is still mixed up with all the other gunk in the cells.

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And we say "release the membrane."

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So, the membrane's like the skin around it.

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Like a balloon or something? - Yup.

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And that melts the skin and the goop inside, then,

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kind of comes out.

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Exactly. So the membrane is made up of phospholipids,

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so, like, fats. And so, if you add detergent to that,

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it'll break it up just like it'll break up grease on a plate.

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Got it. Okay.

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So then we've added rubbing alcohol --

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- So that's the next step. Exactly. - Okay.

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So you've got your DNA, but it's mixed in with

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- all this other stuff in the cell that you don't want. - Mm-hmm.

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And DNA has an interesting property where, if you add rubbing alcohol,

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or even ethanol, it'll precipitate out of solution.

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Which means that it will form a solid when it used to be in solution.

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And that's because, like, the alcohol evaporates quicker or something

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and what's left is porridge.

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The way that I usually think about it is that

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DNA likes to dissolve in water,

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but it doesn't like to dissolve in alcohol.

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So it's kind of, like, scared out of the water.

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And when it hits the interface between the water and the alcohol

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it kind of forms just a solid right there.

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Huh. That's how Michael Phelps did it.

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[ cheering ]

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So then go through then -- so what happens?

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Then the alcohol dries, and we stick the goopy stuff back in the water?

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So, yeah, what you'd end up with is

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you'd have, like, a little pellet of dried up DNA.

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Which is also not useful,

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because you ultimately need it to be in a liquid form

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for most of the tests that you do.

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So you just add some water, wait a little bit, heat it up,

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and then it re-dissolves and you've got pure DNA in liquid form.

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[ woo! ]

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Wow, that's really cool.

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It's pretty cool and it's really easy.

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Especially if you do it with something like strawberries,

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that have tons of DNA.

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[ hey! ] [ groan ]

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All right, well, kids, do try this at home.

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Amaze and amuse your friends.

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Okay, that's it. DNA extraction.

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[ whoop ]

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Why would anyone want to extract DNA?

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How do you extract DNA?

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[ hey! ]

Full Transcript