Source: Zeraati et al., Nat Chem, 2018 When you think about DNA, the first thing that probably comes to mind is the double helix popularized by Watson and Crick (discovered by Rosalind Franklin). However, in the 90s scientists identified a particular conformation in DNA molecules in vitro (in a tube): single chain knot-like loops that they called i-motifs. These structures form because instead of the typical pairing of cytosine – guanine among the two strands of DNA, the cytosines on one chain bind each other forming a brief section that protrudes from the double helix as a four-stranded structure.