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DNA Twisted Into a Never-Before-Seen Shape in a Living Cell

The double helix of the DNA molecule, shaped like a twisted ladder, graces the cover of DIY genetics tests and high school biology textbooks worldwide. First identified in 1953, the has taken on a symbolism that lives on outside of the world of genetics. But the truth is, it’s just one of few shapes that DNA can take. This year, scientists confirmed the existence of another one that for years had proved mysterious and elusive.

For decades, scientists have proposed the “human telomeric i-motif,” a shape that looks distinctly different from the twisted ladder we’re used to. But until the Nature Chemistry paper published this April, this “i-motif” had never been seen in a living cell. Study author Mahdi Zeraati, a Ph.D. student at the Garvan Institute of Medical Research in Sydney, had tracked the i-motif down in a sample of human cells and became the first to ever identify them there.

Up close, the i-motif actually looks a bit like a clump and differs from the double helix we know and love in an important way. The double helix is elegantly organized via bonds between four bases that make up the “rungs” of its famous ladder: cytosine, thymine, adenine and guanine. These bases usually follow predictable rules: adenine on one strand bonds to thymine on the other, and the cytosine on one strand seeks out a guanine on the other.

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