How DNA works

Jan 20, 2006 4:22 PM

Key
Adenine, Thymine base pair
Guanine, Cytosine base pair
Helical backbone

'The key to life'
DNA's double helix holds the key to life. The secret discovered by Watson and Crick in 1953 is that there are four possible types of rung on the ladder formed by the double helix.

There are A-T rungs, where adenine bonds to thymine, T-A rungs where thymine bonds to adenine, C-G rungs where cytosine bonds to guanine, and G-C rungs where guanine bonds to cytosine. No other combinations are possible due to the shape of the four substances.

The outer helices of the DNA molecule, coloured blue on our model, are made up of a chain of circular sugar molecules, each bearing a phospate group. Biochemists call the helices "the sugar-phosphate backbone".

There are about 2.85 billion rungs on the ladder of human DNA. The initial letters of the rungs spell out the sequence of the human genome, the blueprint for each generation of new life.

DNA Replication Gene Expression 1 2 3 4 5 6 The double-stranded DNA molecule is held together by four chemicals called bases. These are adenine (A), cytosine (C), guanine (G) and thymine (T). Where one strand has an adenine base, the other must have a thymine, and where one has a cytosine, the other must have a guanine.