Nucleic Acids:

Living organisms are complex systems. Hundreds of thousands of proteins exist inside each one of us to help carry out our daily functions (see our Fats and Proteins module for more information). These proteins are produced locally, assembled piece-by-piece to exact specifications. An enormous amount of information is required to manage this complex system correctly. This information, detailing the specific structure of the proteins inside of our bodies, is stored in a set of molecules called nucleic acids.

The nucleic acids are very large molecules that have two main parts. The backbone of a nucleic acid is made of alternating sugar and phosphate molecules bonded together in a long chain, represented below:

sugar	phosphate	sugar	phosphate	...

Each of the sugar groups in the backbone is attached (via the bond shown in red) to a third type of molecule called a nucleotide base:

nucleotide base		nucleotide base
|		|
sugar	phosphate	sugar	phosphate	...

Though only four different nucleotide bases can occur in a nucleic acid, each nucleic acid contains millions of bases bonded to it. The order in which these nucleotide bases appear in the nucleic acid is the coding for the information carried in the molecule. In other words, the nucleotide bases serve as a sort of genetic alphabet on which the structure of each protein in our bodies is encoded.