ABSTRACT
The ability of cells to maintain a high degree of order in a chaotic universe depends upon the accurate duplication of vast quantities of genetic information carried in chemical form as DNA. Occasional genetic changes enhance the long-term survival of a species through evolution, the survival of the individual demands a high degree of genetic stability. Since many mutations are deleterious, no species can afford to allow them to accumulate at a high rate in its germ cells. Although the observed mutation frequency is low, it is nevertheless thought to limit the number of essential proteins that any organism can depend upon to perhaps 30,000. All organisms duplicate their DNA with extraordinary accuracy before each cell division. DNA polymerase performs the first proofreading step just before a new nucleotide is covalently added to the growing chain. On their own, most DNA polymerase molecules will synthesize only a short string of nucleotides before falling off the DNA template.
