How does genetic engineering Works

Any discussion of genetics makes reference to DNA (deoxyribonucleic acid), a molecule that contains genetic codes for inheritance. DNA resides in chromosomes, threadlike structures found in the nucleus, or control center, of every cell in every living thing. Chromosomes themselves are made up of genes, which carry codes for the production of proteins. The latter, of which there are many thousands of different varieties, make up the majority of the human body's dry weight.

Although it is central to the latest advances in modern genetic research, DNA was discovered more than 130 years ago. In 1869 the Swiss biochemist Johann Friedrich Miescher (1844-1895) isolated a substance, containing both nitrogen and phosphorus, that separated into a protein and an acid molecule. He called it nucleic acid, and in this material he discovered DNA. Some 74 years would pass, however, before scientists recognized the function of the nucleic acid Miescher had discovered. Then, in 1944, a research team led by the Canadian-born American bacteriologist Oswald Avery (1877-1955) found that by taking DNA from one type of bacterium and inserting it into another, the second bacterium took on certain traits of the first. This experiment, along with other experiments and research, proved that DNA serves as a blueprint for the characteristics and functions of organisms.

The Double Helix
Nine years later, in 1953, the American biochemist James D. Watson (1928-) and the English biochemist Francis Crick (1916-) solved the mystery of DNA's structure and explained the means by which it provides necessary instructions at critical moments in the course of cell division and growth. They proposed a double helix, or spiral staircase, model, which linked the chemical bases of DNA in definite pairs. Using this twisted-ladder model, they were able to explain how the DNA molecule could duplicate itself, since each side of the ladder is identical to the other; if separated, each would serve as the template for the formation of its mirror image.

The sides of the DNA ladder are composed of alternating sugar and phosphate molecules, like links in a chain, and consist of four different chemical bases: adenine, guanine, cytosine, and thymine. The four letters designating these bases—A, G, C, and T—are the alphabet of the genetic code, and each rung of the DNA molecule is made up of a combination of two of these letters. Owing to specific chemical affinities, A always combines with T and C with G, to form what is called a base pair. Specific sequences of these base pairs, which are bonded to each other by atoms of hydrogen, constitute the genes.