Final answer:
RNA polymerase does not need a primer for initiation of transcription, unlike DNA polymerase, which requires a primer to start synthesizing a new DNA strand. The enzyme begins RNA synthesis de novo by adding nucleotides complementary to the DNA template strand.
Step-by-step explanation:
Unlike DNA polymerase, RNA polymerase does not require a primer to initiate transcription. The process of transcription begins when RNA polymerase binds to a DNA template strand at the promoter region. In eukaryotes, this process requires the assistance of transcription factors, which first bind to the promoter sequence and then recruit the RNA polymerase. However, it is the RNA polymerase that ultimately synthesizes RNA from the DNA template. Because RNA polymerase does not need a primer, it can initiate RNA synthesis de novo, adding ribonucleotide 5' triphosphates (ATP, UTP, CTP, GTP) to the growing RNA strand based on complementary base pairing with the DNA template.
Primer Requirement in DNA Replication
In contrast, DNA replication involves DNA polymerase, which is incapable of starting a new strand without a pre-existing 3' hydroxyl (OH) group. Thus, a primer is necessary for DNA polymerase to function. This primer is typically a short RNA sequence synthesized by the enzyme primase.