DNA - A MARVELEOUS MOLECULE
 Deoxyribonucleic acid (DNA) is the genetic blue print of life, many children will have heard of DNA cloning and finger printing, and perhaps genetically modified organisms. However for many DNA is abstract and intangible. These activity sessions aim to improve their understanding of DNA structure and function. They will learn that DNA is a blueprint for almost all living organisms and that this blueprint is written as a code. It will be explained that this code is conserved across the species and that it is the order of the code that accounts for the differences between themselves and others.
(image from http://academy.d20.co.edu/kadets/lundberg/dnapic.html)
To download a short PowerPoint presentation of DNA please click here. (157k)
Activity 1 - Making a DNA model
 The DNA molecule is a double helix, each spiral strand has a sugar phosphate backbone and attached nucleotide bases. The spiral strands are held together by specific interactions between complementary base pairs, adenine (A) with thymine (T) and cytosine (C) with guanine (G). It is the order (sequence) of the bases which gives rise to the DNA code.
This is a very clever model, which when printed onto thin card gives a very good idea of how the bases are attached to the backbone, and the idea that bases of DNA are complimentary to each other.
To download your DNA model as a PDF file click here (PDF 228kb). Print the model onto thin card and use sticky tape to stick it together. You can join lots of these models together for a truly stunning effect.
Activity 2 - Breaking the DNA code
DNA contains a fascinating code, which children love to try and break. It is the sequences of the bases in DNA which give rise to differences between us and different species. This activity will heighten awareness of the DNA code and how it can be broken. There is also an advanced DNA decoding exercise, which will require access to the internet.
To download the files for this activity click on these links
Standard Geometric Code (PDF 17k), Translating DNA (PDF 9k) & Advanced DNA Decoding (PDF 56k).
Activity 3 - DNA Spooling and DNA agarose gel electrophoresis
DNA can be isolated from a variety of different sources, but one of the best ways to demonstrate how DNA can be recovered and analysed is to use a DNA spooling kit. A good example can be purchased from Sigma, which uses salmon sperm DNA.
(http://www.sigmaaldrich.com/catalog/search/ProductDetail/SIGMA/D8666)
For an instruction sheet click here (PDF 30k).
The DNA, when isolated can be analysed using agarose DNA gel electrophoresis. This is a technique employed in many molecular biology science laboratories.
The DNA molecule has an overall negative charge, which means that when DNA is loaded onto a gel and an electric current passed through the gel, the DNA will migrate to the positive electrode. The DNA will migrate a certain distance according to its size, with smaller DNA fragments moving more quickly.
The DNA can be analysed using these small battery powered gel tanks and visualized using staining with Azure A dye. The dye binds to the phosphate backbone of the DNA molecule, and the DNA shows up as a red band.
These fabulous DNA electrophoresis tanks can be purchased from the National Centre for Biotechnology Education (NCBE). They are very easy to use, are priced very reasonably and give excellent results. http://www.ncbe.reading.ac.uk/NCBE/MATERIALS/DNA/menu.html
Activity 4 - Making a DNA necklace
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There is nothing like isolating your very own DNA to bring alive its importance in making us who we are. In this activity DNA is isolated from cheek cells and precipitated in alcohol. The precipitated DNA is placed into a glass vial which can be taken home and worn as a necklace.
 This kit can be purchased from BioRad, they offer an educational discount, and also provide excellent support material.
BioRad DNA necklace web link
Download files for this excersise (PDF 34k) |
Activity 5 - Investigating Chromosomes
DNA is found in the nucleus of a cell, where it is bundled together into chromosomes. It is remarkable how such a long molecule can be packaged to fit inside a small space. This packaging could be demonstrated by winding string (representing DNA) around cardboard tubes (to represent histone proteins, around which DNA is coiled).
Humans have 46 chromosomes, 22 pairs of autosomes and 1 pair of sex chromosomes. This complete set of chromosomes is called a karyotype.
Click on this link (PDF 104k) to try and karyotype a set of human chromosomes, beware it is more difficult than you think!
You could then go on and take a look at how chromosomes are inherited. Biology labs online (http://www.biologylabsonline.com/) do a very good computer based exercise on Mendelian inheritance using drosophila flies (Flylab).
Linking the activities together
- Make the DNA model to show structure and base pairing
- Break the DNA code to illustrate function
- Isolate DNA from Salmon and from human cheek cells, discuss why you would want to isolate DNA
- Analyse DNA using DNA electrophoresis, this will emphasise that the DNA molecule from both salmon and human looks exactly the same when analysed in this way
- Advanced DNA decoding to show that differences lie within the code.
- Explore the idea of DNA packaging and chromosomes
- Begin the theory of inheritance using FlyLab.
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