The entire genetic content of a cell is known as its genome. A cell’s DNA, packaged as a double-stranded DNA molecule, is called its genome. In prokaryotes, the genome is composed of a single, double-stranded DNA molecule in the form of a loop or circle. The region in the cell containing this genetic material is called a nucleoid.
In eukaryotic cells but not in prokaryotes, DNA forms a complex with histone proteins to form chromatin, the substance of eukaryotic chromosomes. Eukaryotic chromosomes are found in a membrane bound nucleus. Eukaryotes also contain mitochondrial DNA (mtDNA) and in the case of plants chloroplast DNA.