The one gene:one enzyme hypothesis emerged from work on which two organisms

one gene–one enzyme hypothesis, idea advanced in the early 1940s that each gene controls the synthesis or activity of a single enzyme. The concept, which united the fields of genetics and biochemistry, was proposed by American geneticist George Wells Beadle and American biochemist Edward L. Tatum, who conducted their studies in the mold Neurospora crassa. Their experiments involved first exposing the mold to mutation-inducing X-rays and then culturing it in a minimal growth medium that contained only the basic nutrients that the wild-type, or nonmutated, strain of mold needed to survive. They found that the mutant strains of mold required the addition of specific amino acids to the minimal medium in order to grow. Using this information, the researchers were able to associate mutations in specific genes to the disruption of individual enzymes in the metabolic pathways that normally produced the missing amino acids. This discovery won Beadle and Tatum the 1958 Nobel Prize for Physiology or Medicine (shared with American geneticist Joshua Lederberg).

Although the hypothesis was amply verified in principle, it has undergone considerable sophistication since the 1940s. Today it is known that not all genes encode an enzyme and that some enzymes are made up of several short polypeptides encoded by two or more genes.

George Beadle had spent two years in T. H. Morgan's lab at Caltech, studying genetics using fruit flies as a model organism. In 1941, he and Edward Tatum turned to an even simpler model for studying genetics. In its normal, or "wild", state, the mold Neurospora crassa can grow on a medium containing just sugar, a small amount of biotin, and inorganic salts.

When the mold is exposed to X-ray radiation, mutations arise in occasional cells. Some of the mutations affect the mold's ability to form organic compounds from simpler building blocks. For example, some lose the ability to assemble particular amino acids. To thrive, those strains need to have the particular amino acids supplied in their nutrient medium or, sometimes, they can make do with precursor compounds that the cells can convert into the required amino acids.

By supplying a variety of compounds in the nutrient medium and seeing which allow various mutant strains to grow and which don't, Beadle and Tatum saw that they could deduce the sequence of biochemical reactions in cells that make necessary compounds like amino acids. The scientists concluded that the function of a gene is to direct the formation of a particular enzyme, which regulates a chemical event. A mutation can alter a gene so it no longer produces the normal enzyme, resulting in a physical symptom, like the need for nutritional supplements. Beadle and Tatum proposed that, in general, each gene directs the formation of one (and only one) enzyme.

For their work, Beadle and Tatum shared, with J. Lederberg, the 1958 Nobel Prize in Physiology or Medicine.

More Information

Reference:

Beadle, G.W., Tatum, E.L., Genetic control of biochemical reactions in Neurospora. Proc Natl Acad Sci, 27(11):499-506. 1941. [PubMed]

What organisms use the study of one gene

Why is the one gene, one enzyme hypothesis?

What is the one gene, one enzyme hypothesis quizlet?

Who proposed one gene