John Craig, Age 14, Of Seattle, Wash., for his question:

What is dna?

We used to say that birds migrate and squirrels hide nuts by instinct. But no one could explain instinct, and now the meaningless word is out of date. Science naw knows that the vital processes and the endless varieties of life are governed by the genetic code  and its master planner is dna.

Chemists study molecules, and biologists study living things. The two fields seemed far apart until biologists probed into the molecules which make up the living cell. Already the results of this molecular biology outshine our total knowledge of all science. There are chemicals called nucleic acids in all living cells, and we now know how they work to govern heredity and the vital processes of life itself.

Deoxyribonucleic acid, known as DNA, works with its sister chemical,

Ribonucleic acid, RNA, to govern the growth and form of every cell in a living organism. The living cells obey their orders to produce a tree or a man. They govern heredity and decide whether your eyes are blue or brown. They decide whether your body has a healthy resistance to this or that disease.

DNA is the chemical computer which carries the blueprints for all the varieties of life and their vital activities. It is present in the genes, those small beads which form long threads called chromosomes in the nucleus of each living cell. Each human living cell has 46 chromosomes and about 100,000 genes, and the DNA it contains is a blueprint for the entire body in structure, the master chemical is two strands of long molecu1es. The strands are coiled in a helix like a double spiral staircase, and each half turn is locked with five cross ties. The strands are made from sugars and phosphoric acid. The cross ties are large molecules called nitrogen bases. There are four different bases, and the order in which they are arranged determines the oars computed by the DNA by  each of the four different bases in DNA is like a code letter. Three bases, we think, are used to form a coded message, and the work of DNA, the computer chemical, is to form countless numbers of these coded messages. RNA, the messenger chemical, copies these coded orders and carries them to fragments of protein to form ribosomes. The ribosomes carry out the coded orders and string amino acids into long molecules of proteins. The proteins are enzymes which govern the vital processes of the living cells.

Basically, it is the same in all plant and animal cells. On account of the arrangement of its bases and perhaps other molecules, each plant and animal obeys its own special orders. In the human cell, the long threads of dna are coiled in the genes of the chromosomes in the nucleus. If the DNA threads in your entire body were uncoiled, they would be long enough to reach to the moon and back.