Explain the biochemical nature of DNA

DNA exists as a double-stranded molecule in nature. The strands are held together by Vander Waals' forces and the purine and pyrimidine bases of the two strands are held together by hydrogen bonding. ... Genetic information is contained in the sequence of mononucleotide of the DNA molecule. DNA has three types of chemical component: phosphate, a sugar called deoxyribose, and four nitrogenous bases—adenine, guanine, cytosine, and thymine. Two of the bases, adenine and guanine, have a double-ring structure characteristic of a type of chemical called a purine. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). To fit inside cells, DNA is coiled tightly to form structures we call chromosomes.