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DNA [Print-version]

In the centre of every plant cell - from algae to sunflowers - and in the centre of every animal cell - from snails to you and me - thereís a copy of the organismís genetic material.

The DNA carries a complete blueprint of the organism. Itís what transfers characteristics from one generation to the next.

At the chemical level the cells of all plants and all animals contain DNA in the same shape - the famous "double helix" that looks like a twisted ladder. Whatís more, all DNA molecules - in both plants and animals - are made from the same four chemical building blocks - called nucleotides. What is different is how these four nucleotides in DNA are arranged.

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Genetics is about storing and passing on messages.

These genetic messages are stored in your DNA, which is inside almost every cell in your body. DNA tells cells what theyíre supposed to do, when, where and how - to keep your body working well.

Our understanding of genetics stems from the discovery of the DNA molecule in every cell, which carries the genetic information.

What is DNA?

DNA is an acid that carries (as genes) all the information which we inherit from our parents. It controls everything about the way you look, from the colour of your eyes to how tall you are to the width of your feet. Your DNA is like your thumbprint. It is yours and yours alone. Unless you have an identical twin, no one else on the planet has exactly the same DNA as you.

James Watson and Francis Crick found out that DNA looks like two threads twisted around each other, held together by many bridges between the strands. It almost looks like a spiral staircase. This shape is called a double helix. The genetic information is stored on the threads.

Where can DNA be found?

In the nucleus of almost every cell in your body, and that of every other living thing, is the collection of DNA needed to make you. DNA in the nucleus is grouped into 23 sets of chromosomes that are called your "genome". In each chromosome, the DNA is grouped into "genes". Your genome contains about 35,000 genes. Each gene carries information that tells the cell to make a unique protein that will perform a special function.

How does something as small as DNA molecules contain all of the instructions to make your whole body and keep it working? Just as a large number of words can be made from only a few letters, so DNA can make lots of different instructions from a few building blocks.

How knowledge about DNA affects us

Scientists are working to understand the genetic messages that make some people respond to medicines differently than others and make some people more prone to certain diseases than others. They use this knowledge to make new medicines to help people live healthier lives.

DST launched a three-year programme to tell South Africans about Biotechnology (see This is the part of science that uses the DNA building blocks of life to make useful products from living things.

From a poster by Rapid Phase (Pty) Ltd for the Public Understanding of Biotechnology programme.