Genetic information is organized into chromosomes, which are much larger than the cell itself. In bacteria and archaea, the DNA is typically circular, with some exceptions. Eukaryotes have linear chromosomes, while mitochondria (and some exceptions) have circular DNA. In bacteria, DNA is supercoiled by topoisomerase, and in eukaryotes, it is wrapped around histones, with archaea potentially using both supercoiling and histones. Extrachromosomal DNA, like plasmids, contains non-essential genes and can be found in bacteria, archaea, and some single-celled eukaryotes, as well as in mitochondria and chloroplasts.