: Transcription is the RNA synthesis from a DNA template, involving a rewriting of the code without a change in its language. Transcription is catalysed by RNA polymerase and is exclusively nuclear in eukaryotic cells (apart from mitochondrial and chloroplast transcription). Topoisomerases are group of enzymes that alter the topological form of DNA. Helicase enzyme unwinds double stranded helical DNA during replication. Ligase, involved in DNA replication in prokaryotes, catalyzes the formation of phosphodiester bonds between adjacent 5-phosphate and the free 3-hydroxy group in DNA duplexes.