of James Watson. The two scientists discovered that they shared the opinion that DNA, not proteins, was the critical factor in passing on genetic information. They both believed that by solving the structure of the DNA, it would lead to an explanation of the self-replication of genes. Crick and Watson's work to understand what role DNA played in the replication of the gene required them to obtain information from many different sources. In 1944, Oswald Avery had discovered that purified DNA, not proteins, was the main carrier of genetic information. This historic discovery set the stage for Crick and Watson to investigate the role of DNA in the gene. Just like any other scientist, Crick and Watson followed their share of false ideas. But what greatly helped these two scientists was their ability to freely criticize eachother without being offensive. One of the great pieces of work by Francis Crick is the three-dimensional model of the DNA molecule which he and Watson produced. The model exhibits the two sides of a flexible ladder coiled around a common center to form a double helix. Each outside of the ladder, also called the backbone, is constant throughout the molecule and repeats the phosphate-sugar bond over and over again. Attached to the inside of the backbone at the sugar is part of the ladder's rung. This variable part of the DNA molecule consists of one of the four bases adenine, guanine, thymine or cytosine. The sequence of these bases along the inside of the ladder determines the genetic message. The key to Crick and Watson's discovery was the realization that because of its size, shape and chemical makeup, each base on one side of the ladder could pair by hydrogen bonds with only one other base on the other complementary side of the ladder. This meant that the large adenine molecule could pair only with the smaller thymine and the large guanine molecule could pair with only smaller cytosine. Once this struc...
