Life their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869. Its molecular structure was identified by James Watson and Francis Crick in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Rosalind Franklin. Life is
Non-helical models of DNA structure Natural Science, 7, (5), 85-100, 2018. The discovery of topoisomerases, enzymes that can change the linking number of circular nucleic acids and thus "unwind" the replicating bacterial chromosome, was largely seen by the mainstream scientific community to satisfy the topological objection to the Watson–Crick helical structure. The later X-ray crystallography data for the nucleosome, which showed a helical DNA structure wrapped around the protein nucleosome core particle, was considered to provide further affirmation for the existence of the helical structure "in vivo". Non-double-helical models are not currently accepted by the mainstream scientific community. Enzymes capable of unwinding and rewinding DNA