Transcription is the process where RNA is copied from DNA. DNA is a made up of two strands which makes a double helix. In order for transcription to occur, the two DNA strands must come apart. The DNA strand is unzipped by DNA Helicase and the RNA nucleotides attach to the exposed DNA through complementary base pairing. Uracil binds to adenine, and guanine binds to cytosine in RNA. An enzyme called RNA synthase forms covalent bonds between the nucleotide bases. Unlike DNA, RNA is single-stranded. A messenger RNA (mRNA) strand is formed and breaks away from the DNA which then re-zips itself up thanks to the natural formation of hydrogen bonds. mRNA is now free to migrate out of the nucleus through a nuclear pore.