There are three main steps to DNA transcription: initiation, elongation, and termination. The process varies depending on whether the cell is prokaryotic or eukaryotic, but the general steps are the same.
Initiation begins when an enzyme called RNA polymerase plus one or more transcription factors bind to the promoter of a particular gene. The RNA polymerase complex then unzips the two strands of DNA and forms a structure that looks like a bubble (only a few bases are unwound at a time).
During the elongation phase, RNA polymerase reads the template DNA strand (also known as the 5’ end) and adds RNA nucleotides to bind to the complementary strand (3’ end). The mRNA is synthesized from the 5’ to 3’ direction.
The termination phase begins when the RNA polymerase complex reaches the termination sequence of a gene. The newly formed mRNA molecule will be freed from the RNA polymerase complex, the two DNA strands will be reformed, and the RNA polymerase complex will be disassembled.