Chase, Martha Cowles (1927- )
Chase, Martha Cowles (1927- )
Martha Cowles Chase is remembered for a landmark experiment in genetics carried out with American geneticist Alfred Day Hershey (1908–1997). Their experiment indicated that, contrary to prevailing opinion in 1952, DNA was genetic material. A year later, James D. Watson and British biophysicist Francis Crick proposed their double helical model for the three-dimensional structure of structure of DNA. Hershey was honored as one of the founders of molecular biology , and shared the 1969 Nobel Prize in medicine or physiology with Salvador Luria and Max Delbrück.
Martha Chase was born in Cleveland, Ohio. She earned a bachelor's degree from the College of Wooster in 1950 and her doctoral degree from the University of Southern California in 1964. Having married and changed her name to Martha C. Epstein (Martha Cowles Chase Epstein), she later returned to Cleveland Heights, Ohio, where she lived with her father, Samuel W. Chase. After graduating from college, Chase worked as an assistant to Alfred Hershey at the Carnegie Institution of Washington in Cold Spring Harbor, New York. This was a critical period in the history of modern genetics and the beginning of an entirely new phase of research that established the science of molecular biology. Including the name of an assistant or technician on a publication, especially one that was certain to become a landmark in the history of molecular biology, was unusual during the 1960s. Thus, it is remarkable that Martha Chase's name is inextricably linked to all accounts of the path to the demonstration that DNA is the genetic material.
During the 1940s, most chemists, physicists, and geneticists thought that the genetic material must be a protein, but research on the bacteria that cause pneumonia suggested the nucleic acids played a fundamental role in inheritance. The first well-known series of experiments to challenge the assumption that genes must be proteins or nucleoproteins was carried out by Oswald T. Avery (1877–1955) and his co-workers Colin Macleod , and Maclyn McCarty in 1944. Avery's work was a refinement of observations previously reported in 1928 by Fred Griffith (1877–1941), a British bacteriologist. Avery identified the transforming principle of bacterial types as DNA and noted that further studies of the chemistry of DNA were required in order to explain its biological activity.
Most geneticists were skeptical about the possibility that DNA could serve as the genetic material until the results of the Hershey-Chase experiments of 1952 were reported. Their experiments indicated that bacteriophages (viruses that attack bacteria) might act like tiny syringes containing the genetic material and the empty virus containers might remain outside the bacterial cell after the genetic material of the virus had been injected. To test this possibility, Hershey and Chase used radioactive sulfur to label bacteriophage proteins and radioactive phosphate to label their DNA. After allowing viruses to attack the bacterial cells, the bacterial cultures were spun in a blender and centrifuged in order to separate intact bacteria from smaller particles.
Hershey and Chase found that most of the bacteriophage DNA remained with the bacterial cells while their protein coats were released into the medium. They concluded that the protein played a role in adsorption to the bacteria and helped inject the viral DNA into the bacterial cell. Thus, it was the DNA that was involved in the growth and multiplication of bacteriophage within the infected bacterial cell. Friends of Alfred Hershey recalled that when he was asked for his concept of the greatest scientific happiness, he said it would be to have an experiment that works. The Hershey-Chase experiments became a proverbial example of what his friends and colleagues called "Hershey Heaven."
See also Bacteriophage and bacteriophage typing; DNA (Deoxyribonucleic acid); Molecular biology and molecular genetics; Molecular biology, central dogma of; Viral genetics