Frederick griffith contribution to dna

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What did frederick griffith discover

In the aftermath of the deadly flu epidemic, governments across the globe rushed to develop vaccines that could stop the spread of infectious diseases. In England, microbiologist Frederick Griffith was studying two strains of Streptococcus pneumoniae that varied dramatically in both their appearance and their virulence , or their ability to cause disease.

Specifically, the highly virulent S strain had a smooth capsule, or outer coat composed of polysaccharides, while the nonvirulent R strain had a rough appearance and lacked a capsule Figure 1. Mice injected with the S strain died within a few days after injection, while mice injected with the R strain did not die. Through a series of experiments, Griffith established that the virulence of the S strain was destroyed by heating the bacteria.

Thus, he was surprised to find that mice died when they were injected with a mixture of heat-killed S bacteria and living R bacteria Figure 2 , neither of which caused mice to die when they were injected alone. Griffith was able to isolate live bacteria from the hearts of the dead animals that had been injected with the mixed strains, and he observed that these bacteria had the smooth capsules characteristic of the S strain.

Griffith experiment notes

Based on these observations, Griffith hypothesized that a chemical component from the virulent S cells had somehow transformed the R cells into the more virulent S form Griffith, Unfortunately, Griffith was not able to identify the chemical nature of this " transforming principle " beyond the fact that it was able to survive heat treatment.

Figure 2 Figure Detail Looking back on Griffith's results, which were published in , the interpretation seems obvious. Today, we know that DNA molecules can renature after heat treatment and that bacteria can take up foreign DNA from the environment by a process that we still refer to as transformation. These facts would not be discovered, however, until other scientists conducted further explorations of the nature and function of DNA.

Figure 3 Figure Detail. At the same time that Griffith was conducting his experiments, researcher Oswald Avery and his colleagues at the Rockefeller University in New York were performing detailed analyses of the pneumococcal cell capsule and the role of this capsule in infections.