Week 4: DNA

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JANET

Hello, and welcome to the final week of the science experiments course. We hope you've enjoyed it so far. The experiments you did last week taught us about the important biological process of respiration. This process is happening in cells only about 100th of a millimetre long, and that's something far too small for us to observe directly without a powerful microscope. But you could get an idea of the strength of the process by measuring the bubbles, which indicate the carbon dioxide being given off by the reaction.

Now, we don't always have to look at very small things using indirect methods. We can be more direct. So this week, you're going to do an experiment which will enable you to look directly at the contents of the nucleus of a cell. You're going to extract and observe DNA-- the material which carries the genetic instructions for the growth and development of life.

All living things contain DNA. And you've probably heard that each person has a DNA code which is unique to them, except for identical twins, who have the same DNA. This uniqueness has led to incredible advances across many areas of science, from our understanding of the evolution of life on earth through to the development of new medical interventions. DNA can even be used to solve crimes.

Your experiment will extract and directly observe the DNA contained inside the cells of a kiwi fruit. Now, you could look at the DNA for many living things, even yourself. But kiwi fruits are simple and straightforward to work with. And on the way, you will learn about how the instructions for life are encoded and passed on. We look forward to discussing your experiment, the science, and even the ethical implications in the forums.

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Welcome to Week 4. This week, you are going to use some fairly common household chemicals to isolate and observe the DNA (deoxyribonucleic acid) from the nucleus of a kiwi fruit.

DNA was first isolated as far back as 1869, but it wasn’t until 1928 that scientists realised that it carried genetic information. In 1953, the structure of the molecule was discovered by Francis Crick and James D. Watson and other colleagues, while working at Cambridge University.

DNA is a molecule containing sequences of chemicals in very specific arrangements. The shape of the molecule is like a twisted ladder, known as a ‘double helix’, which contains stretches of chemicals, known as genes, which code for certain biological traits and functions. In other words, DNA contains the instructions by which organisms build and maintain their existence.