Thymine

Thymine
Chemical name	5-Methylpyrimidine-2,4(1H,3H)-dione
Chemical formula	C5H6N2O2
Molecular mass	126.11334 g/mol
Melting point	316 - 317 °C
CAS number	65-71-4
SMILES	CC1=CNC(NC1=O)=O

For the similarly-spelled vitamin compound, see Thiamine

Thymine, also known as 5-methyluracil, is a pyrimidine nucleobase. As the name implies, thymine may be derived by methylation of uracil at the 5th carbon. Thymine is found in the nucleic acid DNA. In RNA thymine is replaced with uracil in most cases. In DNA, thymine(T) binds to adenine (A) via two hydrogen bonds to assist in stabilizing the nucleic acid structures.

Thymine combined with deoxyribose creates the nucleoside deoxythymidine, which is synonymous with the term thymidine. Thymidine can be phosphorylated with one, two or three phosphoric acid groups, creating respectively TMP, TDP or TTP (thymidine mono- di- or triphosphate).

One of the common mutations of DNA involves two adjacent thymines or cytosine, which in presence of ultraviolet light may form thymine dimers, causing "kinks" in the DNA molecule that inhibit normal function.