Deoxyribonucleic Acid (DNA), genetic material of all cellular organisms and most viruses. DNA carriesthe information needed to direct protein synthesis and replication. Protein synthesis is the production of the proteins needed by the cell or virus for its activities and development. Replicationis the process by which DNA copies itself for each descendant cell or virus, passing on the information needed for protein synthesis. In most cellular organisms, DNA is organized on chromosomeslocated in the nucleus of the cell.
Structure of DNA A molecule of DNA consists of two chains, strands composed of a large number of chemical compounds,called nucleotides, linked together to form a chain. These chains are arranged like a ladder that hasbeen twisted into the shape of a winding staircase, called a double helix. Each nucleotide consists ofthree units: a sugar molecule called deoxyribose, a phosphate group, and one of four different nitrogen-containing compounds called bases. The four bases are adenine (A), guanine (G), thymine (T),and cytosine (C). The deoxyribose molecule occupies the center position in the nucleotide, flanked bya phosphate group on one side and a base on the other. The phosphate group of each nucleotide is also linked to the deoxyribose of the adjacent nucleotide in the chain. These linked deoxyribose-phosphatesubunits form the parallel side rails of the ladder. The bases face inward toward each other, formingthe rungs of the ladder.