DNA (DeoxyriboNucleic Acid), shown as a double helix or twisted ladder, whose structure was worked out by Watson & Crick. DNA is the most complex molecule known. It has a two strands of alternating sugar and phosphate and these are joined (like rungs in a ladder) by pairs of bases. Bases interlock in a fixed way to form these base pairs and so each strand of the double helix mirrors the information in the other. This information (the base sequence) is how DNA stores genetic information (the genetic code).