Describe the process of transcription.

Transcription is the process of using DNA from the nucleus of a cell as a template to synthesise mRNA (messenger RNA). An enzyme called DNA helicase unwinds and unzips the DNA at the start of the gene (called the promoter region of the gene) by breaking the hydrogen bonds between complementary DNA bases. Another enzyme, RNA polymerase then uses the exposed antisense strand of DNA as a template to synthesise a complementary mRNA molecule using the complementary base pairing rule (G to C, C to G, T to A, A to U). RNA polymerase docks at the promoter region of the gene, reading the antisense strand of DNA in the 3' to 5' direction and synthesising RNA in the 5' to 3' direction, catalysing the formation of phosphodiester bonds between the RNA nucleotides. When the RNA polymerase reaches a STOP codon, it stops transcribing the DNA. The mRNA is released from the DNA template and the DNA reforms into a double helix. The mRNA can then be exported from the nucleus and into the cytoplasm, where it can be translated into a polypeptide. It is important to note that both DNA helicase and RNA polymerase require ATP for their roles.