The Simplest Way to Replicate DNA

Replication process

We’re now ready to discuss the replication process in more detail. As illustrated in the figures given below (top), the two complementary DNA strands running in opposite directions around a circular chromosome unravel, starting at ori. As the strands unwind, they create two replication forks, which expand in both directions around the chromosome until the strands completely separate at the replication terminus (denoted ter). The replication terminus is located roughly opposite to ori in the chromosome.

An important thing to know about replication is that a DNA polymerase doesn’t wait for the two parent strands to completely separate before initiating replication; instead, it starts copying while the strands are unraveling. Thus, just four DNA polymerases, each responsible for one half-strand, can all start at ori and replicate the entire chromosome. To start replication, a DNA polymerase needs a primer, a short complementary segment (shown in red in the figure below) that binds to the parent strand and jump starts the DNA polymerase.