DNA was first recognized and identified by the Swiss biologist, Johannes Friedrich Miescher in 1869 during his research on white blood cells . DNA: DNA is a double helical long polymer of deoxyribonucleotides . The length of DNA is usually defined as a number of nucleotides (or a pair of nucleotides referred to as base pairs ) present in it. This also is the characteristic of an organism . DNA contains a sugar-phosphate backbone , and the nucleotide bases ( guanine, cytosine, adenine, and thymine ). Thecoding segment of DNAis called theexon.A segment of DNA within a gene that encodes a sequence ultimately translated into a protein product. So, DNA is a polymer of nucleotide bases.