The Discovery of ‘Supercoiled’ DNA

by Meghna Kumar

The popular “double-helix” model of DNA can be found in nearly every biology textbook at both the high school and college level. But new research may show that this model no longer holds true and that DNA actually coils into a “menagerie” of strands.

In 1953, biologists James Watson and Francis Crick discovered what is now known as the double-helix model of DNA, which portrays DNA as double-stranded with a sugar-phosphate backbone and nitrogenous bases in the center. Combined, the sugar-phosphate backbone and one nitrogenous base create a nucleotide. They believed that in DNA, the sugar in the backbone was deoxyribose and was held together with phosphodiester bonds. They believed that the nitrogenous bases were paired to their corresponding nitrogenous base with hydrogen bonds. Hydrogen bonds are easier to break, which they believed would allow for DNA replication.

According to Rossitza Irobalieva, a biochemist at the Baylor College of Medicine in Houston, “Some of the circles [of DNA] had sharp bends, some were figure eights, and others looked like handcuffs or racquets or even sewing needles. Some looked like rods because they were so coiled.” Compared to Watson and Crick’s 12 base pairs, scientists now hypothesize that there are approximately 3 billion base pairs and that DNA structure may be even more complex.



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