What is a gene ?
Relationship of a DNA transcriptional unit to its transcribed RNA product:

    RNA is transcribed from the template strand of DNA. As with all nucleic acids syntheses, the RNA product is transcribed 5' 3'. The signal for the start of transcription is the promoter, which is 'upstream' (that is, 5' to) with respect to the sense strand of the DNA. The first transcribed base is several bases downstream (that is, 3' to) from the promoter. Transcription then proceeds to a signal sequence at the termination site. The transcribed product thus includes a 5' untranslated region (5'-UTR) upstream from the the begining of translation at the start codon, and a 3'-UTR downstream from the end of translation at the stop codon. These, like the intron regions, will be removed before the protein product is translated from the RNA.

Figure modified after © 2002 by Griffiths et al. ; text © 2011 by Steven M. Carr