One Gene One Enzyme Hypothesis

One Gene One Enzyme Hypothesis
Introduction
George Beadle and Coworker Edward L.Tatum proved that the information coded within DNA of a chromosome is used to specify particular enzymes.
Method of Study

• Beadle and Tatum created Mandelian in the chromosomes of the fungus call Neurospora by the use of the x-rays.
• They studied the effect of the mutations caused by them and suggested “one gene one enzyme hypothesis”

Choice of Material

• They choose the bread mold, neuropora crassa as an experimental organism. It had a short life cycle and was easily grown on a defined medium, containing known substances, such as glucose and NaCl.
• The nutrition of Neurospora could be studied by its ability to metabolize sugars and other chemicals the scientist could add or delete from the mixture of the medium.

Production of Mutations

• The induced mutations in Neurospora spores by using x-rays.
• The mutated spores were placed on complete growth media enriched with all necessary metabolites, so keeping the strains alive because the strains were deficient in producing certain compounds necessary for fungus growth due to damaged DNA by earlier irradiation, hence called Mutants.

Identification of Mutant Strains

• To test the mutations, they grew the mutated strains on the animal media containing sugar, ammonia, salt, a few vitamins and water.
• A strain that had lost the ability to make a necessary metabolite, failed to grow on such media.
• Using this approach they succeeded in identifying and isolating the different mutants.

Identification of Specific Mutations

• To determine the specific nature of each mutation, they added various chemicals to minimal media, to make the strains grow.
• Using this technique, they were able to pinpoint the biochemical problem and thus the genetic deficiency of the mutants.
• Many of the mutants were unable to synthesize a single amino acid or a specifc vitamin.
• If a spore lacked the ability to synthesize a particular amino acid, such as Arginine, it only grew if the Arginine was added in the growth medium Such mutants were called as arg mutants.
• Chromosomes mapping studies on the organism facilitated their work and they mapped three areas clusters of mutant Arginine genes.
• For each enzyme in the arginine biosynthetic pathway, they were able to isolate a mutant strain with a defective form of that enzyme and mutation always proved to be located at one of a few specific chromosomal sites, different for each enzyme.

Conclusion
They concluded that genes produced effects by specifying the structure of enzymes and that each gene encodes the structure of a single enzyme. This was called “One gene one enzyme hypothesis”.