The structure of Deoxyribosenucleic acid (DNA) is given which has originated life. The life depends on arrangement of nucleotides in DNA and the arrangement of nucleotides depends on enzymes produced by influence of life. The structure of enzymes is also briefly discussed. It is enunciated that a sequence of 3 nucleotide determines the position of one amino-acid. The concept that the genes control the structure of enzymes is supported. A symmetrical pattern in the genetic code is tabulated and the physiology of DNA is discussed at considerable length.