Welcome to You Ask Andy

Michael Slosarz, age 13, of Indianapolis, Indiana, for his question:

What exactly is DNA?

Not so long ago, it was said that the behavior of animals was governed by instincts    and the word instinct was used to explain many other mysterious happenings. However, even the scientists could not explain what instinct was. Then in the 1960s, six Nobel Prizes were awarded to researchers who discovered DNA. This was the scientific highlight of the decade. For one thing, it replaced the vague old concept of instinct with a precise understanding of what really governs the activities of all living animals and plants.

This story begins with the molecule, that tight package of interlocked atoms. In most non living substances, single molecules throng together to form solids, liquids and gases. Plants and animals form more complex materials, with small molecules linked together in durable chains. These form hydrocarbon chemicals from hydrogen and carbon, plus several other elements. Such a giant molecule is a polymer.

The sciences of molecular biology and x ray crystallography explore the living cell for miraculous organic polymers. The cell is a semi fluid unit of turbulent chemical activity around the tiny, dense nucleus. It is the nucleus which directs all the busy cellular activity. It contains the chromosomes and the genes that carry the blueprint of instructions from generation to generation.

In the 1960s, researchers discovered that the genes are stuffed with long polymers called deoxyribonucleic acid, alias DNA. The structure of this amazing molecule is a double helix    a pair of threads twisted like a spiral staircase. Its ingredients are common elements packaged in small simple molecules and linked together. The ropy sides of the double ladder are sugars and phosphates. The more complex rungs that link the two sides are nitrogen compounds called bases..

Only four different bases are used. They are the chemical compounds adenine and thyamine, cyctosine and guanine    or A and T, C and G. Each rung is a link of two bases. But A links only with T and C links only with G. A rung may be TA or AT, CG or GC. These four can be arranged in countless different sequences    for example, two Ats, followed by six GCs, CG and so on. The order of the bases carries the coded DNA blueprint that governs the structure and life activities of every plant or animal.

Every human being inherits a unique DNA blueprint from his or hef ancestors. Duplicates are packed into the nucleus of each cell. Their directions are transmitted and carried out by other miraculous chemicals outside the ducieUs. The DNA blueprint governs the body's structure and growth, its features, its tendencies to health or disease and to some extent ids mental and emotional talents. And every p2isons' DNA is unique    different from everyone else's.

One human DNA molecule may contain 10,000 rungs. The tightly rolled spirals in the nucleus of one cell may be a yard long. The total length of DNA wound up in a human body man be 20 billion miles long. Researchers are probing to decode its countless items. Perhaps someday they will learn how to correct such items as the DNA signals that cause tendencies to human sicknesses.

 

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