Image courtesy U.S. National Library of Medicine The double helix. See more DNA pictures.

Like the one ring of power in Tolkien's "Lord of the Rings," deoxyribonucleic acid (DNA) is the master molecule of every cell. It contains vital information that gets passed on to each successive generation. It coordinates the making of itself as well as other molecules (proteins). If it is changed slightly, serious consequences may result. If it is destroyed beyond repair, the cell dies.

Changes in the DNA of cells in multicellular organisms produce variations in the characteristics of a species. Over long periods of time, natural selection acts on these variations to evolve or change the species.

Thank You Thanks to Jon-Paul Powers for his assistance with this article.

The presence or absence of DNA evidence at a crime scene could mean the difference between a guilty verdict and an acquittal. DNA is so important that the United States government has spent enormous amounts of money to unravel the sequence of DNA in the human genome in hopes of understanding and finding cures for many genetic diseases. Finally, from the DNA of one cell, we can clone an animal, a plant or perhaps even a human being.

But what is DNA? Where is it found? What makes it so special? How does it work? In this article, we will look deep into the structure of DNA and explain how it makes itself and how it determines all of your traits. First, let's look at how DNA was discovered.

Public domain image "The Double Helix" is James Watson's historical account of the discovery of DNA's structure.

DNA is one of a class of molecules called nucleic acids. Nucleic acids were originally discovered in 1868 by Friedrich Meischer, a Swiss biologist, who isolated DNA from pus cells on bandages. Although Meischer suspected that nucleic acids might contain genetic information, he could not confirm it.

In 1943, Oswald Avery and colleagues at Rockefeller University showed that DNA taken from a bacterium, Streptococcus pneumonia, could make non-infectious bacteria become infectious. These results indicated that DNA was the information-containing molecule in the cell. The information role of DNA was further supported in 1952 when Alfred Hershey and Martha Chase demonstrated that to make new viruses, a bacteriophage virus injected DNA, not protein, into the host cell (see How Viruses Work for more information).

So scientists had theorized about the informational role of DNA for a long time, but nobody knew how this information was encoded and transmitted. Many scientists guessed that the structure of the molecule was important to this process. In 1953, James D. Watson and Francis Crick discovered the structure of DNA at Cambridge University. The story was described in James Watson's book "The Double Helix" and brought to the screen in the movie, "The Race for the Double Helix." Basically, Watson and Crick used molecular modeling techniques and data from other investigators (including Maurice Wilkins, Rosalind Franklin, Erwin Chargaff and Linus Pauling) to solve the structure of DNA. Watson, Crick and Wilkins received the Nobel Prize in Medicine for the discovery of DNA's structure (Franklin, who was Wilkins' collaborator and provided a key piece of data that revealed the structure to Watson and Crick, died before the prize was awarded).

Next, we'll look closely at DNA's structure.

Animal vs. Plant DNA The DNA of all living organisms has the same structure and code, although some viruses use RNA as the information carrier instead of DNA. Most animals have two copies of each chromosome. In contrast, plants may have more than two copies of several chromosomes, which usually arise from errors in the distribution of the chromosomes during cell reproduction. In animals, this type of error usually causes genetic diseases that are usually fatal. For some unknown reasons, this type of error is not as devastating to plants.