Coding strand

By convention, the coding strand is the strand used when displaying a DNA sequence. It is presented in the 5' to 3' direction.

Wherever a gene exists on a DNA molecule, one strand is the coding strand (or sense strand), and the other is the noncoding strand (also called the antisense strand, anticoding strand, template strand or transcribed strand).

Strands in transcription bubble

During transcription, RNA polymerase unwinds a short section of the DNA double helix near the start of the gene (the transcription start site). This unwound section is known as the transcription bubble. The RNA polymerase, and with it the transcription bubble, travels along the noncoding strand in the opposite, 3' to 5', direction, as well as polymerizing a newly synthesized strand in 5' to 3' or downstream direction. The DNA double helix is rewound by RNA polymerase at the rear of the transcription bubble. Like how two adjacent zippers work, when pulled together, they unzip and rezip as they proceed in a particular direction. Various factors can cause double-stranded DNA to break; thus, reorder genes or cause cell death.