Transfer of a ubiquitin molecule to another protein, usually signaling destruction of that protein, but in some cases ubiquitylation acts as a chemical tag in epigenetic processes.
A common pyrimidine found in RNA, it base pairs with adenine and is replaced by thymine in DNA. Methylation of uracil produces thymine. It turns into thymine to protect the DNA and to improve the efficiency of DNA replication. Uracil can base pair with any of the bases depending on how the molecule arranges itself on the helix, but readily pairs with adenine because the methyl group is repelled into a fixed position.