DNA Replication

Every time a cell divides, it copies its DNA and passes one copy to each daughter cell. This process of creating a copy of the DNA is called DNA replication.

It begins during the S phase of the cell cycle, when the DNA helix starts to unwind.

The enzyme DNA helicase acts like a zipper, breaking the base pair bonds and separating the two strands.

Now, one of the separated strands serves as a template for the formation of a new strand.

Another enzyme, DNA polymerase, moves along the template strand, reading the bases and adding complementary nucleotides to build the new strand. Special base-pairing rules ensure the correct order—adenine pairs with thymine, and guanine pairs with cytosine.

Once completed, each new double-stranded DNA molecule has one old and one new strand. This process is called semiconservative replication because half of the original DNA is conserved in each new copy.