For 10 points, name this nucleobase which is unique to RNA and forms base pairs with adenine.
A monophosphorylated version of this substance is used to treat orotic aciduria. This chemical's 5-bromo, 2-deoxy version is a common label to assay cell cycle progression in flow cytometry, and its 5-fluoro version is an antimetabolite. During glycogen synthesis, glucose monomers are conjugated to a derivative of this molecule, which acts as a carrier. A polymer of this substance was used by Marshall Nirenberg and Heinrich Matthaei in a classic experiment that produced a polymer of phenylalanine, which showed that the codon for phenylalanine was three of this nucleotide. For 10 points, name this nucleobase which is unique to RNA and forms base pairs with adenine.
A monophosphorylated version of this substance is used to treat orotic aciduria.
uracil [or uridine; accept UMP, UDP, or UTP]