DNA is a molecule in the shape of a helix. It is illustrated in a right handed curve (see illustration below). Each strand, made up of a sugar-phosphate backbone and attached bases is connected to its complimentary strand by a non-covalent hydrogen bond. For a closer look at these bases, take a look at our models at The Base Site. The bases are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). A and T are connected by two hydrogen bonds, G and C are connected by three. There are about ten nucleotide pairs per helical turn. For more information on the bases, check out our article: A, T, C, G: How DNA gets turned on.The scientists James Watson and Francis Crick first described this structure in 1953.

Everytime a cell reporoduces through mitosis, the DNA must copy itself so that the new cell will know what to do. In order to go through this process, called replication, the DNA molecule unwinds and splits. And enzyme called DNA plymerase moves up the strands matching the correct bases, forming two new sets of DNA. The new set of DNA moves into the new cell. A always bonds with T and G always bonds with C.

 

This picture shows the unwound DNA molecule and the base pairs. For closer models of these bases, go to The Base Site.

This picture show the unwound DNA and the new strands being made. The correct bases match up and two new strands of DNA are made -- one for the old cell and a replicate copy for the new cell.

 

This image is a closeup of what the unzipped DNA strand would look like. Notice the base pair matchups and nucleotide bonds. For a closer look at the bases pictured at right, check out The Base Site.