DNA Replicates Itself

One of the cool things about DNA is that it is able to make an exact copy of itself - in other words, it's able to replicate. This is necessary, to do when cells want to divide.

In order for the two new cells to be identical, the original cell first has to replicate its DNA, then divide the replicated DNA evenly between the two new cells. Let's take a look now at how DNA replicates.

There are four simple steps to replication:

1. The double helix unwinds, and the two strands separate.
   
   
2. Next to each separated strand, an enzyme called DNA polymerase lines up nucleotides to form new second strands. The enzyme lines up nucleotides according to the base-pairing rules.
   
   Adenines are paired with thymines, and thymines are paired with adenines. Guanines are paired with cytosines, and cytosines are paired with guanines.
   
   
3. Hydrogen bonds form between the base pairs, forming the new "rungs" of the DNA ladder. Bonds form between the sugar-phosphate components of the newly aligned nucleotides so that each newly formed ladder has a new side, too.
   
   
4. The new double-stranded molecules twist up into double helices.

Let's start with one DNA molecule.

The strands separate and for each strand, the cell makes a new complementary strand, and we end up with two new, but identical, DNA molecules. The original DNA molecule has replicated.