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My Genes, Myself

Dip your toes into the genome pool of knowledge

By Michael Mechanic

Most of an organism's critical functions are carried out by proteins, which consist of long chains of amino acids folded into biologically active forms. Some types of proteins include antibodies (which help rid the body of foreign invaders), enzymes (which catalyze key chemical reactions), receptors (which carry messages across cellular membranes) and structural proteins.

A gene is a piece of DNA that provides instructions for manufacture of a single protein or, in some cases, another biologically important molecule. The total human DNA, or genome, is thought to contain some 100,000 genes, which are located along long stretches of DNA called chromosomes. Human cells contain 23 pairs of chromosomes--one member of each pair inherited from each parent.

Although every cell in an animal contains the entire DNA blueprint, certain genes--and therefore, certain proteins--are expressed in only some cells and are turned off in others. Brain cells, for example, don't need to make hemoglobin, whereas blood cells do. Insulin, a protein hormone, is made only in the pancreas, and collagen, a structural protein, is an important component of skin cells.

Some non-coding portions of the DNA--those that do not specify a protein or biological molecule--are key in regulating when and where in the animal a gene is expressed. The majority of human DNA, however, has no known function and some scientists consider it "junk."

In order for a gene to be expressed, the DNA double-helix is partly unwound and one strand of the DNA is copied in the form of a short-lived messenger molecule called Messenger RNA (mRNA). The mRNA is then processed and transported to the ribosomes--the cellular protein-making machines--where it is used as a template for protein synthesis. In some cases, the RNAs themselves--which can play biological roles other than that of messenger--are the end product.

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From the Dec. 21-27, 1995 issue of Metro

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