the compound was not fully understood until 1953 when Francis Crick and James Watson made their famous suggestion that DNA existed as a double helix in the journal Nature (“DNA History”, 2004). DNA was first isolated in 1869 by Friedrich Miescher, and nearly a full century passed before the Nobel prize was awarded to Watson and Crick for the structural determination of the compound (“DNA History”, 2004). This determination was made using a technique called x-ray diffraction, where x-rays are shot through a specimen, diffracted onto a screen or film, and the resultant pattern is analyzed to give the original structure, a technique still widely used today in modern biochemistry (Suryanarayana, 1998, p.4). Watson went on to become the director of the National Center for Human Genome Research. The Human Genome Project, or project to map the entire human DNA code, was a major revolution in science that gained much media attention in the last two decades (“DNA History”, 2004).
The full chemical name for DNA is deoxy-ribo-nucleic acid, so names because it lacks the hydroxyl group that at the 2’ position found in the RNA sugar ring (Calladine, 2004, p.242). DNA is a polymer, or a compound that exhibits many repeating monomer units. Because each individual monomer of DNA is a nucleotide, it is referred to as a polynucleotide (Hallick, 1995). Each nucleotide monomer consists of three distinct pieces: a phosphate group, the 5-carbon sugar (deoxy-ribose), and one of four nitrogen containing bases attached to the sugar. The four nitrogen containing bases are adenine and guanine, collectively referred to as the purines, and cytosine and thymine, collectively referred to as the pyrimidines. Purines and pyrimidines differ in the composition of their ring structure (Hallick, 1995). When a nucleotide is bound to a sugar and a phosphate, it is called a nucleotide, but when it is bound to just a sugar with no phosphate, it is called a nucleoside (Hallick,