Supercoiled DNA is more dynamic than “Watson-Crick” double helix

Since Sir Francis Crick first discovered DNA we have known that the physical structure of the fundamental building block of life is a “double helix,” but a new study says that we now have the technology to determine the actual shape of DNA.

And its actually much more complex:

“The beautiful double-helical structure we all know and love is not the actual active form of DNA,” explains Dr. Lynn Zechiedrich, who is a department of molecular virology and microbiology professor at Baylor College.

The study contributor worked alongside Dr. Wah Chiu, who is a professor in the Verna and Marrs McLean Department of Biochemistry and Molecular Biology.

Zechiedrich goes on to say, “Previous studies were on short fragments (6 – 12 base pairs) of linear DNA, but human DNA is constantly moving around in your body – and it coils and uncoils. You can’t coil linear DNA and study it, so we had to make circles so the ends would trap the different degrees of winding.”

supercoiled-dna
Scientists have created some new images of the three-dimensional structure of supercoiled DNA. (Photo : Thana Sutthibutpong)

Study co-lead author Dr. Rossitza N. Irobalieva, also of Baylor, describe how the team used cryo-electron tomography—which is a powerful microscopy technique involving freezing biologically active material—to examine first three-dimensional structures of individual DNA molecules. She reported further that the coiling actually caused many different shapes (not just the simple double helix).

She notes, “Some of the circles had sharp bends, some were figure-8s, and others looked like racquets or sewing needles. Some looked like rods because they were so coiled.”

Finally, co-lead author Dr. Johnathan Fogg comments, “Being able to observe individual DNA circles allows us to understand the different structures of biologically active DNA. Each of these different structures facilitates how DNA interacts with proteins, other DNA and RNA, and anticancer drugs, adapting to the cell processes required.”

Reference

Irobalieva RN, Fogg JM, Catanese DJ, Sutthibutpong T, Chen M, Barker AK, Ludtke SJ, Harris SA, Schmid MF, Chiu W, Zechiedrich L. (2015) Structural Diversity of supercoiled DNA. Nature Comm [Epub ahead of print]. [article]

Source – Pioneer News