Two nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are found in living things which serve to store, translate, and pass on the genetic information of an organism to the next generation. Nucleic acids are universal to all life, in eukaryotic and prokaryotic cells, as well as in viruses. The mitochondria of eukaryotic cells also contain some DNA, known as mitochondrial DNA.
Nucleic acids have a special physical structure that lets them be the information chemicals of living things. DNA and RNA are both giant molecules consisting of long chains of small, repeating chemical units called nucleotides joined together like the box cars of a train. Each nucleotide unit carries a single piece of information, corresponding to an individual letter in a word; when nucleotides are strung together in long chains, the nucleic acids contain messages corresponding to words and sentences. The information in the genes (lengths of nucleic acid) in the nucleus is translated by cells into polypeptides and proteins in the cytoplasm. The cell then can read these "words" and know what to do.
Proteins are important because they make up cell structure and because they function as enzymes, which are catalysts which control the various biochemical pathways in cell metabolism.
There are important differences between the two nucleic acids. DNA has two long chains, or strands, of nucleotides that mirror each other and which are arranged in a double helix format. RNA has a single strand. Furthermore, the four bases of the nucleotides of DNA are adenine, cytosine, guanine, and thymine, while those of RNA lack thymine, which is substituted by uracil. The DNA, copies of which are found in every cell of the body, represents the permanent copy of an organism's entire genetic information, which is passed on to the next generation. The RNA is never more than a temporary copy of a small fraction of the information. There are three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). DNA serves as the master set of blueprints for all of an organism's functions, and RNA acts as the specialist that interprets a small portion of these instructions for use in the cells and tissues of the organism. In short, living organisms use the nucleic acid DNA to preserve their biological information and the nucleic acid RNA to access it.