In the transcription process, RNA polymerase functions to copy a DNA sequence into an RNA sequence. It does this by reading the DNA template and synthesizing a complementary RNA molecule. More specifically, RNA polymerases catalyze the generation of phosphodiester bonds between nucleotides, linking them together to form a linear RNA chain. As the RNA polymerase moves along the DNA, it unwinds the double helix ahead of its active site, exposing a new region of the template strand for complementary base pairing. This allows the RNA polymerase to extend the growing RNA chain one nucleotide at a time in the 5′-to-3′ direction. Because RNA polymerase promptly releases the newly synthesized RNA strand from the DNA as it progresses, numerous RNA copies can be generated from the same gene in a short period. This allows for the initiation of additional RNA synthesis even before the completion of the first transcript. When RNA polymerase molecules closely follow one another (each moving at a speed of approximately 20 nucleotides per second), over a thousand transcripts can be produced from a single gene within an hour. On a side note, RNA polymerases can initiate an RNA chain without a primer, unlike DNA polymerase which can’t.