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thymidylic acid[¦thī·mə¦dil·ik ′as·əd]
a complex natural compound. Thymidylic acid is a mononucleotide consisting of the pyrimydine base thymine, the carbohydrate deoxyribose, and a phosphoric acid residue. The compound takes the form of fine acicular crystals that are readily soluble in water; its molecular weight is 322.2. Thymidylic acid is contained in all living cells as a component of deoxyribonucleic acid (DNA). It is formed by methylation of deoxyuridylic acid. By adding two phosphoric acid residues, thymidylic acid becomes thymidine triphosphoric acid (TTP), which, under the action of the enzyme DNA-polymerase, becomes part of the growing polynucleotide DNA chain.