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A pyrimidine that is one of the five organic bases found in the nucleic acids of cells. In DNA it pairs with adenine. Uracil replaces thymine in RNA.

Thymine is part of thymidine, a corresponding nucleoside, in which it is chemically linked with the sugar deoxyribose. It is also part of thymidylic acid, a nucleotide, which is a phosphate ester of thymidine.

Melting point 321°–325°C.

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