DNA structures refer to the three-dimensional arrangement of nucleotide bases in a DNA molecule. The most well-known structure of DNA is the double helix, which consists of two intertwined strands of nucleotides that form a twisted ladder-like structure. Other DNA structures include Z-DNA, which has a left-handed spiral shape, and G-quadruplexes, which are four-stranded structures formed by guanine-rich sequences. Studying DNA structures is important for understanding how genetic information is stored and how it can be manipulated for various applications in biotechnology and medicine.