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Laboratory Investigation IV: DNA Extraction Lab

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • DNA Lab Introduction 0:06
    • Purpose
    • Materials
    • Time
  • Part I 2:06
    • Pour Sports Drink Into the Small Cup
    • When Time Expires, Spit Into the Cup
    • Add Cell Lysate Solution
    • Let it Sit for a Couple Minutes
  • Part II 4:10
    • Slowly Add Cold Ethanol
    • DNA Will Creep Up Into the Ethanol Layer
  • Analysis 5:59
  • DNA Structure Connection 8:49
    • DNA is Microscopic
    • Visible DNA
    • Extracted DNA

Transcription: Laboratory Investigation IV: DNA Extraction Lab

Hi, welcome back to, this is laboratory investigation 4, DNA extraction lab.0000

A little introduction to the DNA lab, then we will talk about the purpose.0008

The purpose is to extract DNA from living human cells.0012

That might seem like that is going to be painful, no, it is a harmless things.0017

You can do it harmlessly, you can get it from epithelial cells.0022

Cells that easily come off from the inside your mouth, from inside of your cheeks.0025

They come off as you are talking, as you are chewing, as you are sucking on a hard candy, whatever.0030

You replace a lot of these cells consistently.0039

It is very harmless to do this.0042

The materials you need, 5ml of sports beverage like Gatorade or Powerade.0045

That is not much, in terms of exactly how much you are going to put in your mouth, 0049

you need about 2ml which is hardly anything.0054

You are not going to swallow it.0058

3 ml of cell lysate solution meant to burst open plasma membranes and nuclear envelopes, membrane of the nucleus.0060

10 ml of very cold ethanol, I recommend freezing it, putting it in the freezer now.0068

The actual alcohol will not freeze, you would need a colder temperature to get solid ethanol.0075

It will be very cold which will maximize the effectiveness of this particular lab.0083

A small cup, even like a little cup that a child would take liquid medicine with.0088

One of those medicine cups like that is big enough.0094

A large test tube and a cap, you need a cap or stopper on it because you are going to be inverting it and flipping around.0098

Test tube rack to keep the test tube upright.0105

Two pipettes, one for putting in the cell lysate solution and one for the ethanol.0108

Here is an illustration of a lovely DNA which we will be extracting and getting to become visible, so we can actually see DNA.0115

The time required, about 30 minutes will suffice.0123

Part 1, you are going to pour 1 to 2 ml of that sports drink in the small cup.0127

Drink the liquid, like you are taking a shot of it, but do not swallow it.0133

You are going to swish it around your mouth for 30 seconds.0137

As you are doing it, you can use your teeth to help dislodge cells.0143

I’m kind of using my teeth to gently bite on the sides of the cheeks.0151

Do not actually bite, do not draw blood.0155

We do not need blood for this lab.0158

Just gently scrape your teeth against your cheeks, that will get more of those epithelial cells0161

from the inside your mouth to get into that sports drink solution.0168

When time expires, when about 30 seconds has come to pass, 0173

spit out the liquid/saliva into the cup and then dump the contents into the test tube.0177

Here is a little test tube rack with two test tubes.0184

You will only need one test tube for this.0187

As long as it is one of the ones that is about that big, that will suffice.0189

After it has been sitting there for a little while, that combination of sports drink and saliva,0195

you are going to add the cell lysate solution.0202

Like I said earlier, this is meant to rupture or break apart the plasma membrane and the nuclear envelope,0205

that way the DNA leaks out of the cells.0212

You spit out thousands and thousands of cells, the great thing is when all that DNA leaks out, 0216

you will have enough genetic material.0220

At this point, you just need to get it out of that solution into a more clear solution, 0222

and get it to all clump together.0228

That is the next part of it.0229

To make sure that cell lysate solution is spread throughout all those cells, 0232

it is going to be really important to cap the test tube and invert it like this 5 times, to mix it.0237

And then, let it sit for 2 to 3 minutes, let that DNA leak out, let it sit.0245

Part 2, tilt the test tube after it has been sitting for 2-3 minutes.0251

Slowly add ethanol, this is the really cold ethanol, drop by drop.0256

You can just add a steady stream, do not add it too fast.0262

You do not want to disturb the gradual leaking of the DNA into the ethanol layer.0267

It is a very delicate process, you want to keep it as still and as calm as possible.0272

If you actually do this lab, you will see what I mean.0279

If you would do it too fast, the success rate is not as good.0282

You are going to add that cold ethanol little by little, until you added about 10 ml.0286

Then, let it sit still, absolutely still, do not hold on and move it around.0291

Let it sit in the test tube in the rack for 10 minutes.0296

You will gradually see DNA slowly creeping up in the tube into that ethanol layer, 0301

which is clear compared to that whatever color the sports drink, let us say it was red.0307

The cell lysate solution is pink.0313

That red layer at the bottom is going to be very distinct from that clear ethanol at the top.0316

As it comes up into that clear ethanol, it is going to look like a wispy cloud or spider webs in a bundle.0321

That is the cotton is another term I have heard, students either call it like the cloud or spider web bundle, or cotton.0332

The DNA, when it comes together, it looks like that.0340

If you are wondering what is this picture, this is a scientist who is actually attempting to get DNA 0343

out of this piece of Neanderthal bone.0349

The extraction of DNA, whether it is from dead tissue or living tissue, can have some important practical applications.0352

Analysis, after it ends up in there where you can see your DNA, let us talk about what we did.0360

Why use a sports drink, why not just swished water or apple juice, why does it have to be a sports drink?0367

A lot of it has to do with the electrolyte salt concentration.0376

It is better, in terms of the cells and not letting them get ruptured prematurely or damaged.0381

In terms of like the electrolyte concentration in your bloodstream, what your cells are used to,0390

a sports drink like Gatorade or Powerade is more in line with that.0395

The electrolyte salt concentrations is the best, in terms of what you are going to swish in your mouth0399

to get those cells into a liquid layer out of your mouth.0405

What is the cell lysate, what is the point?0410

As I mentioned before, that breaks open the membrane.0412

Without breaking open the plasma membrane, that breaking up of the nuclear membrane,0415

you are not going to get that DNA effectively, leaking out of that little sac within the bigger sac, the cell membrane.0419

Why ethanol, if you are wondering why do we have to use ethanol and why does it need to be cold?0427

The reason why it is ethanol is DNA would not dissolve in it.0433

If you talk about the solubility of having certain substances dissolve in certain liquids,0437

the important thing here is you do not want the DNA to dissolve.0446

If the DNA dissolves through out it, it will not be visible, it will be spread out throughout it.0448

You want the DNA to stay clamped up and not dissolve.0452

The fact that DNA is not soluble completely in ethanol, you will be able to visualize it.0456

Why does it need to be cold?0463

Molecules are less likely to dissolve and spread out, things kind of slow down the colder it is.0464

It is just kind of the best environment, in terms of getting that DNA up into the ethanol and stay in clumps together.0472

This image right here it is a model of ethanol.0480

If you are wondering why you are looking at, the black part here is carbon.0484

You are looking at hydrogen 1, 2, 3, 4, 5, 6 hydrogen atoms.0492

I’m going to write 5 because the O is the red thing here.0500

This is what makes it an alcohol, it is having that OH.0508

C₂H₅, it is really there are 6 H but the OH right here, that little hydroxide is what makes this ethanol.0511

You can have propanol with 1 carbon or methanol with 3, but ethanol works very well for this particular lab.0521

The connection of DNA structure and why is it so important.0531

DNA is microscopic, but all of the DNA in one human cell, if you would take it all out and0534

stretch it out as like a single DNA double helix, from all 46 chromosomes, it would stretch over meter.0540

To the point where I cannot even stretch my hands,0547

and to the point where you would see them in this view like you are seeing right now.0549

Over 3 feet long, 1 meter, I even heard some estimates like up to 6 feet, almost 2 meters.0553

Which is incredible, in terms of how much DNA is wound up in and jam packed into a microscopic nucleus.0561

The amazing thing is, with all that length of that DNA double helix, it would still be microscopic.0567

It is like you could do like an invisible jump rope with your DNA.0574

We need to extract DNA from thousands and thousands of cells and get it to clump together, it is visible.0578

It looks like that wispy cloud, cotton, spider web, whatever you think it might look like.0584

Extracted DNA could be used for analysis of DNA fragments, mutations, parental tests, who committed the crime,0589

comparing DNA from a suspect to what was found at the crime scene, 0597

in terms of do you know who this person is that was here and committed this crime.0601

In terms of fragmenting DNA, in terms of splitting it up into pieces, and then analyzing how big those pieces are,0606

in terms of where they were different site in terms of the bases of DNA, that is talked about earlier on in this course.0615

This is electrophoresis, a very practical and interesting application, in terms of extracting DNA from cells and making it useful to us.0623

Thank you for watching