The blueprint of life is programmed into the genetic material and would, for a human being, fill at least a million typed pages. What kind of molecule is it that can store so much information inside each and every living cell, even though the cell is often not more than a hundredth of a millimetre across?
    We know that DNA (deoxyribonucleic acid) is the carrier of our hereditary characteristics and that it is based on two strands twisted about one another forming a double helix. The strands consist of alternating carbohydrate and phosphate molecules. On each carbohydrate sits one of the four nitrogenous molecules Adenine, Cytosine, Guanine and Thymine. A DNA strand can thus be compared with a long sentence (sequence) of code words, where each word consists of three letters that can be combined in many different ways, e.g. CAG, ACT.
    Each code word can be read by components inside the cell and translated into one of the twenty amino acids that build proteins. The three-dimensional structure, and hence the function, of the proteins is determined by the order in which the different amino acids are linked together according to the genetic code.
    Proteins are the cell's most important tools. In function as enzymes they maintain all the reactions needed for supporting life.

Introduction »
Site-directed mutagenesis reprograms DNA »
Tailor-made proteins »
The PCR method – a copying machine for DNA molecules »
The PCR method already of great use »
DNA and the genetic code »
Landmarks in the history of gene technology »
Further reading »