DNA or deoxyribonucleic [dee-ahk-see-ry-boh-noo-KLEE-ihk] acid was first isolated by a Swiss chemist Johann Friedrich Miescher in 1869, but over 80 years passed before the function of DNA was understood.
DNA in eukaryotes is contained in the chromosomes of the nucleus. It is like a library that strores the vital information of the cell.
DNA is composed of nucleotides. Each nucleotides is composed of three parts: a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogen base. Each nucleotide in DNA contains one of four different nitrogen gasses - adenine [AD-neen], guanine [GWAH-neen], thymine [THY-meen], or cytosine [SY-tuh-seen].
DNA is composed of two long nucleotide chains as was concluded by James Watson and Francis Crick. Each chain has a backbone od phospohate and sugar. The backbone of the two chains are parallel to one another. The bases chains face each other and fit together. Hydrogen bonds hold the nitrogen gases together.
Watson and Crick showed that the sugar-and-phosphate backbones are twisted in a spiral, a bit like a twisted ladder. This is called a double helix. The ladder sides are the sugar-phosphate-chains, and the ladder rungs are complementary pairs of nitrogen bases.