Banana DNA

Age

Elementary School, Middle School, High School

Format

Hands-on

Material

   Banana
   Blender
   Gauze
   Ice cold ethanol (200 proof)
   Wooden skewer
   Spoon
   Two 50mL centrifuge tubes for each participant
   DNA extraction solution
       30 mL/L soap
       0.3 g/L EDTA
       8.8 g/L NaCl
       4.4 G/L citrate 

Safety Precautions: Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

Preparation

Make sure the ethanol is very cold - you may wish to keep it in a cooler with dry ice.

For a large group, you may want to pour out the necessary amounts of the ethanol and extraction solution ahead of time. You may not want to chop the onion/mash the banana too far in advance, since it goes bad sitting out in the air.

Demonstration

You may want to introduce this demonstration using the dialogue in the "What to say" section below.

Ideally, students should wear gloves when they participate in the DNA extraction to practice good safety technique. However, with a large group of students, this is not practical. Since the chemicals used aren't dangerous, it is ok to skip using the gloves, but do explain to the students that chemists working with dangerous chemicals always wear gloves and that they should still be careful not to spill. Their hands may get sticky, so tell them to wash them afterwards.

Onions are more like people than you might think. They use DNA to produce proteins and duplicate calls, too.

Do any of you know farmers that grow onions?

Scientists spend years using sophisticated equipment to study DNA very carefully. We can't show you how to do that, but we can help you take a quick look at DNA by extracting it from this onion.

Everyone needs two of these centrifuge tubes. I'm going to give you a spoonful of onion that I've pulverized in this blender. By breaking the onion down into tiny bits, we've exposed lots of cells that used to be on the inside of the onion.

Now I'm going to pour about 15mL of a DNA extraction solution into all of your tubes. The solution is mostly dish soap and salt -the soap breaks down the cell walls that contain the DNA, the salt helps separate the DNA from the rest of the molecules in the cell.

Gently mix the solution in with the onion pulp so that the chemicals in the solution touch every bit of the onion. Now you've got DNA floating around in your tube, but I bet you can't see it! We need to get rid of everything else in there first.

Now put the gauze on top of your second centrifuge tube. Push down on the gauze to make a little indentation. Pour your solution onto the indentation and lit it drain. Once nothing more is being strained, throw away the gauze and the pulp.

Now I'm going to give each of you about 20mL of cold ethanol. The ethanol will dissolve most of the material in the tube, leaving just the DNA behind.

Can you see little strings in the ethanol? That's DNA!! It's just like the DNA in your own cells.

You can pull the DNA out of the tube using a wooden skewer.

If you take more precaution when you do this experiment, you can get more DNA from the onion. Bananas work even better. Search online for "DNA Extraction" for more information, if you're interested.

What to Say

Does anyone know what DNA is? Do you want to see what it looks like? We can show you! First, you need to know a little about it.

DNA stands for deoxyribonucleic acid

DNA is your body's instruction manual for living - it's a molecule that stores information that it transfers to another chemical (RNA) which tells your ribosomes, little machines in almost every one of your cells, how to make the proteins that make your body work.

Proteins can send messages, eliminate unwanted viruses and bacteria, and even break down food to give you energy.

DNA is made up of four different building blocks called base components.

   Adenine, called "A"
   Guanine, called "G"
   Cytosine, called "C"
   Thymine, called "T" 

The bases combines in different patterns to store ant kind of information the body needs to operate.

These building blocks combine into bigger structures:

A and T or C and G can combine to make a base pair.

A base pair, a sugar molecule, and a phosphate molecule can combine to make a nucleotide.

Nucleotides string together to form genes, which are make from so many base components combined in such a specific order that they represent some information.

Genes link together to form long strings called chromosomes.

All the chromosomes in your body are collected into a single genomes that's made up of about three billion base components. Almost all of your cells contain two copies of your full genome. Your DNA gets coiled up into a shape called a double-helix - it looks kind of like a double helix. If you unwound it all, it would stretch about six feet!

Almost every type of living creature on Earth uses DNA, just like humans. It's the information stored in the DNA that makes us different than other organisms.

You get your DNA from your parents - whatever information their DNA held is passed onto you. This is called genetic inheritance.

About 99% of your genome is the same as mine - every human being has almost exactly the same DNA. It's the small differences that give some people blonde hair, some people brown eyes, and even make you more likely to get certain diseases.

The double-helix shape of the DNA makes it easy to duplicate. Imagine cutting a spiral staircase in half - it would be easy to figure our where you need to complete each step on each side to make two new staircases.

If your body ever needs another skin cell, an existing skin cell will split its DNA in half to create two copies: one for the old cell and another for the new one.