Transcription is the process in which a gene's DNA sequence is copied to form a messenger RNA molecule. The DNA molecule unwinds due to the action of DNA helicase. RNA nucleotides complementary base pair with the DNA template strand via hydrogen bonds. Thymine bases are replaced by Uracil in the produced mRNA molecule. RNA polymerase binds to the DNA template strand at the promoter region, forming the sugar-phosphate backbone of the mRNA molecule.