Transforming principle
From EvoWiki
The "transforming principle" experiments were a set of studies important in discovering that genetic material is DNA.
The first of the experiments was a study of Streptococcus pneumoniae by Frederick Griffith in 1928. Griffith studied the effects of two strains of S. pneumoniae in mice - Type S (which has a smooth colony morphology) is a virulent strain with a polysaccharide shell that protects against the immune system. Type R (rough colony morphology) is not virulent. Griffith found that when injected into mice:
- Type S killed the mice
- Type R did not kill the mice
- Heat-killed type S did not kill the mice
- Mixtures of type R and heat-killed type S did kill the mice
The heat killed type S bacteria must have transformed the type R bacteria into a virulent strain.
In 1931 M.H. Dawson and R.H.P. Sia showed that heat-killed Type S cells transformed R cells into genetically stable type S cells.
In 1944, Oswald Theodore Avery with Maclyn McCarthy showed that DNA was the substance that was transforming the bacteria, by using Colin M. MacLeod's techniques for purifying the DNA to remove the associated proteins. It was a while before the idea that DNA was the genetic material was accepted because it was previously thought that DNA was too simple to carry information, and that some form of protein was a more likely candidate. Avery, McCarthy and MacLeod showed that purified "transforming principle" contained no protein and was unaffected by the proteases trypsin and chymotrypsin, lipases or RNase (an RNA hydrolysis enzyme), but was deactivated by DNase (the DNA equivalent of RNase). This led to the research that identified DNA as the universal genetic molecule.
During his research Avery wrote to his brother: "sounds like a virus" and "could be a gene", showing that he was aware of the significance of his research.
References
- Garrett, R.H. & C.M. Grisham, 1998. Biochemistry, 2nd ed. Saunders College Publishing, Orlando FL. Ch 29.
- National Library of Medicine, The Oswald T. Avery Collection: The Discovery of the "Transforming Principle" [1]
- WikiPedia: Griffith's experiment
|
This page is part of the EvoWiki encyclopedia of genetics and molecular biology. Topics: Genetics - Transmission genetics - Molecular genetics - Population genetics - Quantitative genetics - Molecular biology - Genomics |
