Extracting DNA from Strawberries

Concert Aria for Mezzo and Piano

Lyrics: Hai-Ting Chinn, inspired by TheSciGuys webcast

Music: Conrad Cummings

 

Extracting DNA from a strawberry

Deoxyribonucleic Acid: DNA

Instructions for how all living cells grow, divide, and behave.

Encoded instructions to build a strawberry—or a strawberry blond.

Materials:

strawberries, fresh, stems removed

Salt

Dish detergent

Sealable plastic bags

70% rubbing alcohol—chilled, if possible

Measuring spoons and cup

Medium mixing bowl

A funnel

A strainer

and tweezers

If you try this at home (and you should)

Do not worry—nothing’s toxic

But don’t drink the solutions we are about to create.

Just for your own good.

to start:

1/3 cup water

1/2 teaspoon of salt

1 Tablespoon dish detergent

stir

put the strawberries into a bag

and measure in

three tablespoons of salt water-soap solution.

Press out air and seal, carefully.

Now I need a volunteer.

Protective clothing for potential spills and splashes!

Please crush these strawberries, salt, and soap into a fine, foamy paste.

It will take about about two minutes.

Squish a strawberry: the cells will burst; their walls will break apart.

Within the walls, the nucleus, where dwells the DNA.

Strawberries are octoploid: each cell contains 8 sets of DNA.

By contrast, human cells are diploid—only two.

That’s why we’re using strawberries instead of you!

The inside of a cell membrane is lipid: that’s grease to a detergent molecule,

Which has two ends: A hydrophilic head, in love with water

Whose molecules are polar (like tiny magnets)

And a hydrophobic tail that quakes in fear at H2O, but happily connects to molecules that are non-polar,

Like oil, or that lipid layer on the inside of a cell membrane.

The detergent’s hydrophobic tail ensnares the lipid layer of the cell wall fragments,

and the hydrophilic head, enchanted by the water, pulls the bits away,

Like lifting oil off of dirty dishes.

The innards of the cell are left behind, including the DNA.

The salt in our solution makes it clump together.

How, and why? Because the salt creates a conductive ionic environment, of course…!

Time’s up! Do we have a fine, foamy strawberry pulp?

Strain into a beaker.

DNA was first isolated in 1869 (much as we are doing now)

But no-one believed that this simple molecule

Could carry the code for the growth, division, behavior, of all known living organisms (and some viruses!).

In 1929, Phoebus Levene identified four nucleic acids:

A for adenine,

C for Cytosine

G for Guanine

T for Thymine,

plus sugars and phosphates.

In the 1940s Edwin Chargaff noticed that amounts of A matched T, amounts of G matched C.

In 1952, Alfred Hershey and Martha Chase put some bacteriophages in a blender,

separated the protein from the DNA

and proved that DNA was indeed the genetic code.

Then Rosalind Franklin, with x-ray crystallography

saw a helix, and some rungs,

that Watson and Crick made a model of, and wrote

A Structure for Deoxyribose Nucleic Acid, The journal Nature April 25, 1953:

And no, they gave Rosalind Franklin no credit at all.

Now 1/2 cup chilled alcohol:

Gently poured onto strawberry foam.

We do not want the two to mix.

Rubbing alcohol, less dense, forms a layer on top.

DNA is not soluble in alcohol: they will not mix together.

But DNA will pull away

from our squished strawberry solution

to gather in cloudy clumps

which we can collect with tweezers

Voilà: strawberry DNA

Deoxyribonucleic Acid: double-stranded helix, with rungs of base-pairs: A-T C-G

Millions in strawberries, billions in us

A-T, C-G: DNA

Encoded instructions for how all cells grow, divide, and behave

To build a strawberry, or a strawberry blond!