Promises and Plasmids
CELLS are very small. About 500 average-sized cells could fit on the period at the end of this sentence. Yet each one of those cells generally contains all the DNA needed to construct a living creature, such as you.
Obviously, if cells are small DNA molecules must be very tiny indeed. They are shaped like long, twisted threads, so long that all the DNA in your body laid end to end would stretch to the sun and back many times! But the threads are very thin, only about one ten-millionth of an inch (1/400,000th mm) across.
To complicate matters, these long, thin threads of DNA must somehow be packed inside the cells, and the only way to fit them in is for them to be twisted up into very tight bundles. This makes it difficult for scientists to locate the exact areas of the particular DNA molecules they may be interested in, the genes. Scientists cannot just put a cell under a microscope, find the gene they want and then extract it with tweezers and put in another gene.
Plasmids to the Rescue
It turns out, however, that bacteria often contain some DNA molecules that are easier to work with. These strands of DNA are more or less independent from the rest of the DNA in the bacteria, forming loops all to themselves that can easily be passed from one bacterium to another. They are called plasmids. At present plasmids are the keys to gene-splicing.
Splicing genes into plants and animals is not so easy because these cells do not have plasmids, and their genetic regulatory systems are much more complicated. But scientists are hopeful that such splicing will soon be possible. If they succeed, then they will be able to put genes in plants from bacteria that fix nitrogen in the soil so that it will not be necessary to add nitrogen fertilizer to the soil. They are also hoping that someday they will be able to cure genetically caused diseases, like sickle-cell anemia, by replacing defective genes in humans.
“A bug is being perfected, which is capable of recovering oil, while others are being programmed to extract metals from below the earth’s surface,” writes Drummond C. Bell, chairman of National Distillers and Chemical Corporation, in Leaders magazine. “The new frontier has already produced, or is on the verge of producing, human insulin to combat diabetes; cancer-fighting interferon made from human cells; and vaccines to prevent diseases such as hepatitis and malaria; as well as hormones to remedy dwarfism and hemophilia, and others that will accelerate the growth of cattle and hogs. Discoveries in progress also include a low-calorie, high-fructose sugar, plants capable of generating their own fertilizer from the air, a strain of wheat with double the protein content of current strains and another variety of wheat that requires a tenth of the water of those farmed today.”
Also, it is now claimed that through gene-splicing a safe, effective vaccine against foot-and-mouth disease in livestock has been produced.—Time, June 29, 1981.
No wonder gene-splicing has suddenly become a big business. However, this shift from laboratory bench to production line has some people alarmed. Why?