Why is a short RNA primer needed for replication?

Step 1 of 3

During DNA replication, the leading strand, which is synthesized continuously in the 5' to 3' direction, does not require an RNA primer. However, the lagging strand, which is synthesized discontinuously in short fragments known as Okazaki fragments, requires RNA primers to initiate each fragment.

Here's how the process works:

1. The DNA helicase enzyme unwinds the double helix, creating a replication fork.

2. DNA polymerase III recognizes the replication fork and begins synthesizing the leading strand by adding deoxyribonucleotides complementary to the template strand.

3. On the lagging strand, DNA polymerase III encounters a region where the template strand is oriented in the opposite direction. This requires DNA polymerase III to synthesize the strand in the opposite direction, creating Okazaki fragments.