DNA stores the instructions for making you, but before your cells can use DNA it has to be "transcribed" into something they can use. To do this, the DNA strands pull apart and RNA, which is a single strand, comes in and matches up with the bases on one of the strands.

The smallest piece of RNA that means something to the cell, is a group of 3 base pairs that is called a codon. Codons tell a cell what amino acid to build. Amino acids are the building blocks of proteins, and proteins are what make the body grow and break down food and carry oxygen to cells - all the things that our bodies need to do to stay alive are based on proteins doing their jobs.

We have a huge amount of DNA in each of our cells. If the DNA from just one of your cells was typed in books, a list of the 3 billion base pairs would fill 200 telephone books. That is from just one cell - and we have trillions of cells in our bodies, and most cells have a complete set of DNA!