Final answer:
RNA polymerase is processive, which means it can synthesize long mRNA strands while moving along DNA. It initiates at the promoter to form mRNA by adding nucleotides complementary to the DNA template strand.
Step-by-step explanation:
The RNA polymerase enzyme is said to be processive because it stays attached to DNA over long stretches of template to make long mRNAs while it remains loose enough to move freely along the template. RNA polymerase binds to a specific sequence on the DNA known as a promoter to initiate transcription. It then unwinds the DNA to form a transcription bubble and synthesizes mRNA in the 5' to 3' direction, adding nucleotides complementary to the antisense strand of the DNA.
DNA-directed RNA polymerase forms an 'open complex' at the promoter site, ensuring fidelity while remaining sufficiently flexible to move along the DNA. During elongation, RNA polymerase aligns nucleic acids with their complementary bases on the DNA template, synthesizing a growing mRNA strand. This process is essential for converting the genetic code from DNA into a form that can be used to synthesize proteins.