Transcription of two genes. (a) RNA polymerase moves from the 3′ end of the template strand, creating an RNA strand that grows in a 5′ → 3′ direction (because it must be antiparallel to the template strand). Note that some genes are transcribed from one strand of the DNA double helix; other genes use the other strand as the template. (b) A uracil is being added to the 3′ end of the transcript for gene 1. Growth is thus 5′ → 3′.