For physics, the period from the beginning to the middle of the 20th century was one of great scientific excitement and revolutionary discovery. The analogous era for biochemistry, and its offspring, molecular biology, was the second half of the 20th century. One of the most important and influential leaders of this scientific revolution was Arthur Kornberg. The DNA polymerase, which he discovered in 1955 and showed to have the remarkable capacity to catalyze the template-directed synthesis of DNA, contributed in major ways to the present-day understanding of how DNA is replicated and repaired, and how it is transcribed. The discovery of DNA polymerase also permitted the development of PCR and DNA sequencing, upon which much of modern biotechnology is based. Kornberg's studies of DNA replication, which spanned a period of nearly 30 years, culminated in a detailed biochemical description of the mechanism by which a chromosome is replicated. The final years of Kornberg's life were devoted to the study of polyphosphate, which he was convinced had a crucial role in cellular function.