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Griffith's experiment



 

Griffith's experiment, conducted in 1928 by Frederick Griffith, was one of the first experiments suggesting that bacteria are capable of transferring genetic information through a process known as transformation.[1][2]

Griffith used two strains of Pneumococcus (which infects mice), a type III-S (smooth) and type II-R (rough) strain. The III-S strain covers itself with a polysaccharide capsule that protects it from the host's immune system, resulting in the death of the host, while the II-R strain doesn't have that protective capsule and is defeated by the host's immune system.

In this experiment, bacteria from the III-S strain were killed by heat, and their remains were added to II-R strain bacteria. While neither alone harmed the mice, the combination was able to kill its host. Griffith was also able to isolate both live II-R and live III-S strains of pneumococcus from the blood of these dead mice. Griffith concluded that the type II-R had been "transformed" into the lethal III-S strain by a "transforming principle" that was somehow part of the dead III-S strain bacteria.

Today, we know that the "transforming principle" Griffith observed was the DNA of the III-S strain bacteria. While the bacteria had been killed, the DNA had survived the heating process and was taken up by the II-R strain bacteria. The III-S strain DNA contains the genes that form the protective polysaccharide capsule. Equipped with this gene, the former II-R strain bacteria were now protected from the host's immune system and could kill it. The exact nature of the transforming principle (DNA) was verified in the experiments done by Avery, McLeod and McCarty and by Hershey and Chase.

See also: Genetics, Hershey-Chase experiment, Oswald Theodore Avery

References

  1. ^ Lorenz MG, Wackernagel W (1994). "Bacterial gene transfer by natural genetic transformation in the environment". Microbiol. Rev. 58 (3): 563–602. PMID 7968924.
  2. ^ Downie AW (1972). "Pneumococcal transformation--a backward view. Fourth Griffith Memorial Lecture". J. Gen. Microbiol. 73 (1): 1–11. PMID 4143929.
  • Avery, MacLeod, and McCarty (1944). "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III". Journal of Experimental Medicine 79 (1): 137-58.
(References the original experiment by Griffith. Original article and 35th anniversary reprint available.)
  • Daniel Hartl and Elizabeth Jones (2005). Genetics: Analysis of Genes and Genomes, 6th edition. Jones & Bartlett.  854 pages. ISBN 0-7637-1511-5.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Griffith's_experiment". A list of authors is available in Wikipedia.
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