The genome of prokaryotes is usually made up of one ''chromosome'' and plasmids. Eukaryota however, contain a larger number of chromosomes - we distinguish two types of eukaryota's chromosomes (nuclear and mitochondrial) and sometimes even plasmids. Most of what we know about the chromosomes of prokaryotes have been obtained from studies of E.coli – it is the organism of choice for such research of prokaryotes. Chromosome consists of double–stranded circular DNA.
Thumbnail: Supercoiling of the DNA in E.Coli is credited to Garasone and is licensed via a Creative Commons Attribution 3.0 Czech Republic.