Deoxyribose is the pentose sugar found in this type of polynucleotide, hence its name Deoxyribonucleic Acid, or DNA. The nitrogenous bases found in DNA are, adenine, guanine, cytosine and thymine. DNA molecules have two polynucleotide chains, held together in a ladderlike structure. The sugar phosphate backbones of the two chains run parallel to each other in opposite directions. Each "rung" of the ladder is a pair of nitrogenous bases, one purine and one pyrimidine extending into the center of the molecule.
The pairing of these bases is always adenine with thymine
(A - T)
and guanine with cytosine
(G - C).
The sugar-phosphate backbones of the two polynucleotide chains coil around one another (making the "ladder" into a spiral "staircase"). This superstructure is known as a "double helix".
DNA acts as the store of genetic information. The sequence of bases along its length are the "language" of the cell and code for all its proteins. DNA is also the molecule of heredity. When a cell or a multicellular organism reproduced either sexually or asexually, the genetic information stored in the DNA molecules is faithfully copied and exact copies of these DNA molecules passed along from one generation to the next.