DNA STRUCTURE

4. Secondary structure (base pairs)

The DNA secondary structure is a double helix (see link below) formed by 2 anti-parallel  DNA strands bind together by hydrogen bonding between bases on opposite strands.

The Java applet below illustrates the bonding between bases (the sugar and phosphate parts of the DNA have been omitted for clarity). Only specific base pairs allows hydrogen bonding. Select 2 bases and click on "Start" to see if the selected bases (A, T, C or G) allows hydrogen bonding.
The specificity of base pairs is due to steric effects and assumes that the bases exist in the keto form.. The double helix is detailed in the next section. The first Watson and Crick model described incorrectly the bases in the enol form

fleche.GIF (105 bytes)  5. Double helix
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