Eva Janda, age 11, of Houston, Texas, for her question:
What does DNA do in the cells?
If we knew all the answers to this question, we could perform miracles. The isolation of deoxyribonucleic acid was the scientific wonder of the 1960's when six Nobel prizes were awarded to researchers who helped to solve its basic structure. Molecular biologists knew that this complex biochemical governed the very life processes of every plant and animal cell and promptly shortened its name to DNA.
The average living cell is too small to be seen and its dynamic nucleus is merely a tiny package in the middle. This vital nucleus is packed with tight coils of long DNA molecules. When uncoiled, the DNA in an average human cell is about a yard long. The total length of DNA is a man's body is estimated to be about 10 billion miles.
The study of minuscule living molecules is not easy. Teams of researchers have been probing the nature of DNA through the past decade and a few of its miraculous secrets have been revealed. We know that the amazing molecule is a coded blueprint that governs every activity in every living cell. From its headquarters, it transmits coded instructions to molecules of ribonucleic acid outside the nucleus.
These mobile RNA molecules are messengers that transmit the DNA instructions to the jellified cytoplasm of the cell. There they trigger certain atoms and other particles to arrange or rearrange themselves into molecules needed to carry on a multitude of biochemical reactions. The cytoplasm is a miniature whirlwind of changing chemical activities. And everything is kept going by RNA messenger molecules that get their instructions from the DNA in the nucleus.
Even when reduced to an infinitesimal size and whizzed at high speed, the general pattern seems quite simple. However, chaos occurs when we recall that an individual cell is merely one of billions in the human body. Things become even more chaotic when we recall that no two human bodies are alike. We wonder how a slender rope of DNA can govern every biological feature and process in every individual human body ¬not to mention every plant and animal.
Apparently the two secrets are in the structure of the DNA molecule and a very complicated system of nature called heredity. The biological features of each individual are governed by DNA packages called genes. Half the assortment is inherited from each parent who inherited an individual assortment from his or her parents. The DNA in each living cell carries an inherited coded blueprint for each individual.
The structure of the DNA molecule is a double helix, somewhat like a double spiral staircase. Its ropy sides are molecules of phosphates and simple sugars. Its rungs are four nitrogen compounds arranged in a special pattern to suit each individual. This pattern is the DNA blueprint that determines the color of skin, hair and eyes, tendencies to health or sickness and all the other biological instructions that make every person one of a kind.