In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

A derivative of this compound prefixed by pseudo- is an important modifier of the T-arm of tRNA, while its fluorine derivative is used to inhibit the enzyme thy-mi-dyl-ate syn-thase, effects of which are essential to its use in chemotherapy. Its N-gly-coy-lase is an important excision enzyme, participation of which explains the absence of Okazaki fragments on the leading strand; it is also essential to protection from damage resulting from deamination of another compound to this nucleotide. First identified in herring sperm, FTP, name this pyrimidine in which the lack of a methyl group is the only difference between it and the nucleotide it replaces, thymine, in RNA.
Science