The Double Helix

Abstract

DNA houses the information needed to transform the phenotype of an organism. The information in the human genome is written out in a linear chain of chemical building blocks or genetic “letters.” These chemical building blocks are commonly referred to as A, C, G, or T, the first letters of their chemical names. The bases A, C, G, and T are not hooked directly to each other. Instead, a long backbone structure runs the length of the DNA molecule, and each base is connected to the backbone. Thus the bases form a DNA chain in the same way that the crossties of a railroad track make a long row of ties, not by connecting directly to each other but rather all by connecting to the same rails that run along the edges. So each base is connected to a segment of the backbone, and the backbone pieces connect to each other, which brings the bases next to each other in a line without the actual bases touching each other. Each building block has a different chemical structure that can be “read” and recognized by the machinery of the cell with an amazingly high level of accuracy. These building blocks, which are known as bases , and the chains of building blocks that can be built from them are called nucleic acids, and DNA is only one of several kinds of nucleic acids present in the cell. The cellular machinery reads these letters at the level of the hydrogen and nitrogen and carbon and phosphorus atoms of which the letters are formed, but one actually needs concern oneself with very little about the real molecular structures of these letters, simply considering each base as a building block.