Table of contents |
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The Search for Genetic Material |
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Transforming Principle |
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The Genetic Material is DNA |
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Properties of Genetic Material (DNA versus RNA) |
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- Despite the simultaneous discovery of nuclein by Meischer and the principles of inheritance by Mendel, it took a considerable time to establish and prove that DNA serves as the genetic material.
- By 1926, the investigation into the mechanisms of genetic inheritance had delved into the molecular realm. Previous findings by notable scientists such as Gregor Mendel, Walter Sutton, and Thomas Hunt Morgan had focused the inquiry on chromosomes within the nucleus of most cells. However, the specific molecule responsible for genetic material remained unidentified.
Before the work of Oswald Avery, Colin MacLeod, and Maclyn McCarty(1933-44), the prevailing thought was that the genetic material was a protein. These researchers aimed to determine the biochemical nature of the “transforming principle” in Griffith's experiment. They purified various biochemicals (proteins, DNA, RNA, etc.) from the heat-killed S cells to identify which ones could transform live R cells into S cells.
Their findings revealed that only DNA from S bacteria could transform R bacteria into S bacteria. Additionally, they discovered that protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect the transformation, indicating that the transforming substance was neither a protein nor RNA. The use of DNase, which inhibits transformation, suggested that DNA was responsible for the transformation.
Avery, MacLeod, and McCarty concluded that DNA is the hereditary material. However, not all biologists were immediately convinced by their findings.
Experiments conducted by Alfred Hershey and Martha Chase in 1952 provided clear evidence that DNA is the genetic material. They focused on bacteriophages, which are viruses that infect bacteria. These viruses attach to bacteria and inject their genetic material into the bacterial cell, which then uses this material to produce more virus particles.
Hershey- Chase Experiment
These experiments demonstrated that DNA, not protein, is the genetic material passed from virus to bacteria.
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Search for Genetic Material
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From the previous discussion, it is evident that the debate over whether proteins or DNA serve as the genetic material was definitively settled by the Hershey-Chase experiment, establishing DNA as the genetic material. However, it was later discovered that in certain viruses, such as Tobacco Mosaic viruses and QB bacteriophage, RNA functions as the genetic material. The question of why DNA is the predominant genetic material while RNA serves dynamic roles as messenger and adapter can be addressed by examining the chemical differences between the two nucleic acids.
Conclusion: Both RNA and DNA can function as genetic material, but DNA is preferred for the storage of genetic information due to its greater stability. RNA is better suited for the transmission of genetic information.
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