Adam Clarke, a fifth-former at Kings High School, asks :-

What is DNA made of?

Warren Tate, a biochemist at the University of Otago, responded.

Every cell, whether it be human, plant, animal or bacterial, contains DNA. The structure of DNA is based around a backbone of carbon, linked to hydrogen, oxygen, nitrogen atoms, and it also contains phosphorus.

DNA has repeats of a smaller three part stucture, a sugar molecule, a phosphate group, and four variations of a base, containing either one or two ring structures This provides four types of unit structures for DNA named for the base, A (adenine), G (guanine), T (thymine) and C (cytosine). The order in which many hundreds of these different units are linked together gives the DNA 'sequence', and is the key to its function as an information store. In humans information for about 100,000 different proteins are stored in this DNA code (the genes!). A huge international effort, called the Human Genome project, aims by 2003 at a cost of 3 billion dollars to determine the order of the 2000,000,000 A,G,C,and T unit structures in our DNA. In the 1950's, James Watson and Francis Crick, working in Cambridge, England, deduced that two strands of DNA wound around each other, with the A ,T, and also the G, C bases forming pairs in the centre, to provide a very regular helical stucture. Watson and Crick realised how this structure allows DNA to be accurately reproduced so that all our cells contains the same DNA structure (and information) as our very first cell.

I hope this helps your understanding of this exciting molecule which today is the subject of an enormous research effort, stemming from the time recombinant DNA technology (genetic engineering) came on stream through the late 1970s and 1980s. This enabled DNA to be studied much more easily.