Scientists have a new theory about the structure of DNA. Two strands of alternating sugar (deoxyribose) and phosphate groups make up the DNA double helix, and the strands were thought to be linked by hydrogen bonds. Reporting in the Proceedings of the National Academy of Sciences (PNAS), a research team from Chalmers University of Technology in Sweden has suggested that hydrogen bonds are not holding the two strands of nucleotide bases together, as has been thought for many years.