DNA and Gene Expression Practice Test

Histone demethylases erase methyl marks on histone tails, reversing methylation to alter chromatin structure and gene expression. These enzymes specifically remove methyl groups from lysine or arginine residues on histone tails, and their activity can either activate or repress transcription depending on the residue and the methylation state. In contrast, methyltransferases add methyl groups to histones, which can tighten or loosen DNA packaging and influence transcription. DNA methyltransferases target DNA itself, not histones, and RNA methyltransferases modify RNA molecules.