Molecular Genetics: DNA Extraction

In this video from our course on molecular genetics, learn all about DNA extraction.

BiologyMolecular Genetics

Transcript

00:08

A la Shmoop

00:11

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

00:14

and we're gonna talk about DNA extraction

00:17

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

00:19

So, Dr. Ruth, why would anyone want to

00:23

extract DNA in the first place?

00:26

What does that do for us?

00:27

Like, when I go to Vermont,

00:29

I understand why I want to extract maple syrup -

00:31

because it tastes good.

00:32

[ pop ] [ mm-mm ]

00:35

Why would anyone want to extract DNA?

00:38

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

00:40

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

00:41

Just like if you wanna study the DNA,

00:43

you should get it out of the cell.

00:44

So, tons of reasons you might wanna do this.

00:46

Let's say you wanna do some forensic testing.

00:49

So you found DNA at a crime scene

00:50

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

00:52

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

00:55

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

00:58

or figure out what the sequence of DNA is

01:00

while it's in someone's cell.

01:01

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

01:03

so you can study it and sequence it.

01:04

Wow, that's really cool.

01:05

So the obvious question is -

01:08

How do you extract DNA?

01:11

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

01:14

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

01:16

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

01:19

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

01:21

is break open the cell.

01:22

And you can do that by grinding them.

01:24

You can often add detergent.

01:26

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

01:29

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

01:31

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

01:34

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

01:35

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

01:38

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

01:40

And you, like, stick it in a bowl

01:42

and it dries and you pound it?

01:44

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

01:46

they would not use that.

01:47

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

01:49

But if you wanna take your cheek cells,

01:51

you basically could just slough them off using Gatorade

01:53

and then spit them in a tube

01:54

and they would kind of --

01:55

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

01:58

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

02:00

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

02:02

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

02:06

- however you did. - [ laughs ]

02:07

And then you would add detergent and salt,

02:10

which basically breaks open the cell membrane

02:12

and the nuclear membrane.

02:13

So that'll kind of release the DNA.

02:15

The problem at that point is that the DNA

02:16

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

02:19

And we say "release the membrane."

02:20

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

02:22

Like a balloon or something? - Yup.

02:23

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

02:26

kind of comes out.

02:27

Exactly. So the membrane is made up of phospholipids,

02:29

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

02:31

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

02:35

Got it. Okay.

02:37

So then we've added rubbing alcohol --

02:40

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

02:42

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

02:43

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

02:45

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

02:48

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

02:51

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

02:56

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

02:59

and what's left is porridge.

03:00

The way that I usually think about it is that

03:02

DNA likes to dissolve in water,

03:04

but it doesn't like to dissolve in alcohol.

03:06

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

03:07

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

03:10

it kind of forms just a solid right there.

03:12

Huh. That's how Michael Phelps did it.

03:13

[ cheering ]

03:15

So then go through then -- so what happens?

03:17

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

03:22

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

03:24

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

03:26

Which is also not useful,

03:27

because you ultimately need it to be in a liquid form

03:28

for most of the tests that you do.

03:30

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

03:32

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

03:35

[ woo! ]

03:36

Wow, that's really cool.

03:38

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

03:39

Especially if you do it with something like strawberries,

03:40

that have tons of DNA.

03:41

[ hey! ] [ groan ]

03:43

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

03:45

Amaze and amuse your friends.

03:47

Okay, that's it. DNA extraction.

03:51

[ whoop ]

03:52

Why would anyone want to extract DNA?

03:55

How do you extract DNA?

03:59

[ hey! ]