Final answer:
A primer is required for DNA polymerase to initiate the synthesis of a new DNA strand during replication. This RNA primer is synthesized by RNA primase and provides the starting 3'-OH group necessary for nucleotide addition.
Step-by-step explanation:
DNA polymerase can only add nucleotides to an existing DNA strand, so a primer is required. This primer is a short strand of RNA that is synthesized by the enzyme RNA primase. The primer provides a free 3'-OH group, which is necessary for DNA polymerase to start adding DNA nucleotides, forming a new strand that is complementary to the template strand. In DNA replication, DNA polymerase extends this RNA primer, adding nucleotides in the 5' to 3' direction. Eventually, the RNA primers are removed and replaced with DNA nucleotides, and the gaps between Okazaki fragments on the lagging strand are sealed by DNA ligase.
DNA polymerase, a crucial enzyme in DNA replication, can only synthesize a new DNA strand by extending an existing template. However, it cannot initiate synthesis on its own. To commence replication, a short RNA or DNA primer, complementary to the template, is essential. This primer provides the starting point for DNA polymerase to add nucleotides in the 5' to 3' direction, extending the growing strand. Primers are synthesized by another enzyme, primase, and serve as a foundation for DNA synthesis during processes like DNA replication, repair, and in vitro polymerase chain reaction (PCR). In summary, the presence of a primer is a prerequisite for DNA polymerase activity in synthesizing new DNA strands.