Structure: Ribonucleic acid (RNA) is a molecule consisting of a long linear chain of nucleotides. Each nucleotide unit is comprised of a sugar, phosphate group and a nitrogenous base. It differs from a DNA molecule in a way that the sugar backbone is a ribose (deoxyribose in DNA) and the bases are adenine, guanine, cytosine and uracil (thymine in DNA).
Compare: deoxyribonucleic acid
See also: nucleic acid