Let's look at a single gene, which consists of a stretch of DNA with some specific control sequences. Near the start of the gene is a region called the promoter. Near the end of the gene is a region called the terminator. The sequence between the promoter and the terminator is the part of the gene that codes for the protein being produced. Transcription begins with initiation when a molecule of RNA polymerase binds to the promoter. The promoter contains a specific sequence of DNA bases that is recognized by the RNA polymerase, allowing it to bind. Notice that the sequence of the promoter plays an important role, even though it isn't part of the protein-coding region of the gene. The RNA polymerase makes its way along the gene, synthesizing the RNA molecule from the template strand of the DNA. Elongation continues until RNA polymerase reaches the terminator, a sequence of DNA nucleotides that marks the end of the gene. Once it reaches the terminator, the RNA polymerase detaches from the DNA, restoring the original DNA double helix, and the newly synthesized RNA floats off.
