The central dogma of molecular biology;
DNA makes RNA makes protein.
Here the process begins.
Transcription factors assemble at a specific promoter region along the DNA.
The length of DNA following the promoter is a gene, and it contains the recipe for a protein.
A mediator protein complex arrives carrying the enzyme RNA polymerase;
it maneuvers the RNA polymerase in to place,
inserting it with the help of other factors between the strands of the DNA double helix.
The assembled collection of all these factors is referred to as the
transcription initiation complex, and now it is ready to be activated.
The initiation complex requires contact with activator proteins, which bind to
specific sequences of DNA known as enhancer regions;
these regions maybe thousands of base pairs distant from the start of the gene.
Contact between the activator proteins and the initiation complex releases the copying mechanism.
The RNA polymerase unzips a small portion of the DNA helix, exposing the bases on each strand.
Only one of the strands is copied;
it acts as a template for the synthesis of an RNA molecule which is assembled
one sub-unit at a time by matching the DNA letter code on the template strand.
The sub-units can be seen here entering the enzyme through its intake hole, and they
are joined together to form the long messenger RNA chains snaking out of the top.