In different classrooms, I have asked, “If I left DNA from a wolf in a test tube alone in a classroom, what would you do?” Some students respond, ‘drink it, so I can get wolf power’. Other students have said, ‘enter the room carefully in case the wolf is angry’. But in reality, we would just come back to DNA.
DNA is not magical. I think it is awesome but it is just a molecule. So what is it?
The full name of DNA is Dexoxyribonucleic acid. Its main function is the storage of information. It is often compared to a recipe and I like that description. If we left a recipe on the kitchen counter for chocolate cake, we wouldn’t expect a chocolate cake to appear (I’ve tried – it doesn’t work). Just like leaving wolf DNA on the counter won’t leave a wolf in the classroom. Recipes need people, ingredients, and machines to make cakes and DNA needs other things in the cell to be ‘read’.
There are 4 bases (or letters) in DNA: A, C, T, G. The order of these bases are the stored information. All living things have DNA with the same structure and bases but the order can change, leading to different things made by cells. Different organisms (humans, wolves, bacteria) use the same storage system but the instructions can be different. Another way to think of DNA is that it is ’the code of life on earth’ (thanks @davidmanly). But remember, DNA is just the information on how to make things and won’t spontaneously create life.
Where is DNA found?
In humans, most of our DNA is found in a protected part of the cell, called the nucleus 1. In all our cells with a nucleus, we have DNA 2. Why do we care where DNA lives? Many reasons but I’ll focus on forensics here. Every cell carries the same DNA information [think about that for a minute... our eye cells carry the same DNA as our heart cells = amazing!]
Because our DNA is the same across our cells, that means you can use a DNA sample from blood and it will match DNA from other cells = skin cells from a fingerprint, sperm cells, or cells in saliva. Note: this is also important in medicine because if you can get the same DNA information from a simple blood test.
What does DNA look like?
I’ve been showing the DNA helix that we see all over the place in this post but DNA doesn’t always look like that. In fact, I’ve never seen this structure except in drawings or models. Some ways that I’ve seen DNA:
If you decide to do a DNA extraction, you will should see the last image. Unfortunately, you need microscopes to see individual strands of DNA (second and third images) and the famous image is rarely seen.
One of the other cool things about DNA is that we get half from our mom and half from our dad. Humans have 23 pairs of chromosomes (long strings of DNA) and we get one of each chromosome from each parent. In other words, one chromosome 1 from dad and one chromosome 1 from mom plus one chromosome 2 from dad and one chromosome 2 from mom…see where this is going? So that means we are a mixture of information from both parents. A great visual representation from @olviakoski on twitter:
David Manly has been kind enough to share some photos of frog tissues (Xenopus laevis) with immunohistochemistry.DNA stains blue.
Updated August 16, 2012:
- Changed the intro, adding the first paragraph. The post was originally written for a grade 7 classroom (thanks @brittgow) and the wolf DNA reference was for them.
- Add the photos from David Manly.