Transcription is the process by which DNA is converted into messenger RNA (mRNA) by RNA polymerase.
RNA polymerase copies both the exons and the introns. The stretch of DNA that is transcribed into an RNA molecule is called a transcription unit.
A transcription unit that is translated into protein contains coding sequence that is translated into protein and sequences that direct and regulate protein synthesis;
Transcription proceeds in the 5' → 3' direction.
Transcription is divided into 3 phases: Initiation, Elongation and Termination..
An animation describing the process of trancription in cells.