Adenine, thymine, cytosine, and guanine are the nitrogenous bases found in the monomeric nucleotides comprising deoxyribonucleic acid (DNA). In eukaryotic cells, DNA would usually be found in the nucleus; extrachromosomal DNA can also be found in mitochondria and chloroplasts.
In prokaryotes (bacteria and archaea), which lack nuclei, DNA can be found as an agglomeration—comprising the chromosome—in the nucleoid region within the cytosol; smaller, extrachromosomal DNA called plasmids can sometimes be found elsewhere in the prokaryotic cytosol, outside the nucleoid region.
