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Archibold Garrod
(1857–1936)
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The one gene-one enzyme hypothesis was first proposed by the English physician Archibald Garrod in 1909. It suggests that each gene codes for a single, specific enzyme.
In the early 1940s American geneticists Edward Tatum and George Beadle evaluated Garrod's hypothesis using the fungus Neurospora. Their findings led to the acceptance of this view. Their key experiments involved exposing the fungus to x-rays, creating mutant strains that were then selected for their inability to grow on a medium that could support the non-mutated form of the fungus. To grow, each mutated strain required the addition of a specific nutritional element to the medium. They found each mutant was blocked at a particular metabolic step that required a particular enzyme that the strain could not produce.
This experiment was of profound importance because it provided a basic explanation of how genes work at the molecular level. However, we now know that the picture is more complex. Not all genes direct the construction of enzymes. Some code for structural proteins, such as collagen or keratin. Moreover, different RNA splicing options can produce distinct polypeptides from the same gene. In addition, some functional proteins, such as the various hemoglobins, are composed of two or more polypeptide chains, derived from two or more different genes. Some genes, such as those for tRNAs do not even code for a polypeptide. However, Tatum and Beadle's work remains significant because it provided, for the first time, evidence that a particular gene produces a particular molecular product.
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Edward Tatum
(1909–1975)
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George Beadle
(1903–1989)
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