How does DNA replication occur?

DNA replication is the process by which a cell makes an exact copy of its DNA before cell division.

Here’s how it happens step by step:

1. Unwinding the DNA:
   The enzyme helicase breaks the hydrogen bonds between the two DNA strands, separating them and forming a replication fork (Y-shaped structure).
2. Binding of primers:
   A short piece of RNA primer is made by the enzyme primase. This primer helps start the new DNA strand.
3. Building new strands:
   • On the leading strand, DNA polymerase adds new nucleotides continuously in the same direction as the fork.
   • On the lagging strand, DNA polymerase makes short pieces called Okazaki fragments in the opposite direction.
4. Replacing RNA primers:
   The RNA primers are later removed and replaced with DNA nucleotides.
5. Joining fragments:
   The enzyme DNA ligase joins all the Okazaki fragments together to make one continuous strand.

In short:
DNA replication =
Unwind → Add primers → Build new strands → Replace primers → Join fragments.

Result: Two identical DNA molecules — each with one old strand and one new strand (called semi-conservative replication).