Deoxyribonucleic acid (DNA) DNA is heredity material. It controls the properties and potential activities of a cell. Location in cell DNA occurs in chromosomes, in the nuclei of the cells and in much lesser amounts in mitochondria and chloroplast. Chemical composition of DNA DNA is made of four kinds of nucleotides; d-adenosine monophosphate (d-AMP) d-guanosine monophosphate (d-GMP) d-cytidine monophosphate (d-CMP) d-thymidine monophosphate (d-TMP) These nucleotides are united with one another through phosphodiester linkages in a specific sequence to form long chains. Two nucleotides join to form dinucleotide e.g nicotinamide adenine dinucleotide (NAD) which is important coenzyme in several oxidation-reduction reactions in the cell. Three nucleotides join to form trinucleotide . Ratio of Bases in DNA In 1951, Erwin Chargaff provided data about the ratios of different bases present in DNA. This data suggested that ade...