Beadle and Tatum’s experiments are important not only for their conceptual advances in understanding genes, but also because they demonstrate the utility of screening for genetic mutants to investigate a biological process — this is called genetic analysis.
Beadle and Tatum’s results were useful to investigate biological processes, specifically the metabolic pathways that produce amino acids. For example, Srb and Horowitz [1944] tested the ability of the amino acids to rescue auxotrophic strains. They added one of each of the amino acids to minimal medium and recorded which of these restored growth to independent mutants.
Watch the video below, BIOL 183: Beadle & Tatum’s One-Gene-One-Enzyme hypothesis, by Susan Bush [2020] at Metropolitan State University on YouTube, which explains the one – gene – one – enzyme hypothesis.
Figure 7.3.1 A Simplified Version of the Arg Biosynthetic Pathway, Showing Citrulline [Cit] and Ornithine [Orn] as Intermediates in Arg Metabolism. These chemical reactions depend on enzymes represented here as the products of three different genes.A convenient example is arginine. If the progeny of a mutagenized spore could grow on minimal medium only when it was supplemented with arginine [Arg], then the auxotroph must bear a mutation in the Arg biosynthetic pathway and was called an “arginineless” strain [arg-].
Synthesis of even a relatively simple molecule such as arginine, requires many steps — each with a different enzyme. Each enzyme works sequentially on a different intermediate in the pathway [Figure 7.3.1]. For arginine [Arg], two of the biochemical intermediates are ornithine [Orn] and citrulline [Cit]. Thus, mutation of any one of the enzymes in this pathway could turn Neurospora into an Arg auxotroph [arg-]. Srb and Horowitz extended their analysis of Arg auxotrophs by testing the intermediates of amino acid biosynthesis for the ability to restore growth of the mutants [Figure 7.3.2].
Figure 7.3.2 Testing Different Arg Auxotrophs for Their Ability to Grow on Media Supplemented with Intermediates in the Arg Biosynthetic PathwayThey found that only Arg could rescue all the Arg auxotrophs, while either Arg or Cit could rescue some [Table 7.3.1]. Based on these results, they deduced the location of each mutation in the Arg biochemical pathway, [i.e., which gene was responsible for the metabolism of which intermediate].
Table 7.3.1 Ability of auxotrophic mutants of each of the three enzymes of the Arg biosynthetic pathways to grow on minimal medium [MM] supplemented with Arg or either of its precursors, Orn and Cit. Gene names refer to the labels used in Figure 7.3.1.Mutants InMM + OrnMM + CitMM + Arggene AYesYesYesgene BNoYesYesgene CNoNoYesThe video below, Gene Interactions P1, by Michelle Stieber [2014] on YouTube, discusses gene interactions and related biochemical pathways.
Media Attributions
References
Bush, S. [2020, April 16]. BIOL 183: Beadle & Tatum’s one-gene-one-enzyme hypothesis [video file]. YouTube. //www.youtube.com/watch?v=4nXX2djQVvI
Deyholos, M. [2017]. Figures: 4. A simplified version of the Arg biosynthetic pathway… and 5. Testing different Arg auxotrophs for their ability to grow…[digital image]. In Locke, J., Harrington, M., Canham, L. and Min Ku Kang [Eds.], Open Genetics Lectures, Fall 2017 [Chapter 3, p. 3]. Dataverse/ BCcampus. //solr.bccampus.ca:8001/bcc/file/7a7b00f9-fb56-4c49-81a9-cfa3ad80e6d8/1/OpenGeneticsLectures_Fall2017.pdf
Srb, A. M. & Horowitz N. H. [1944]. The ornithine cycle in Neurospora and its genetic control. Journal of Biological Chemistry, 154, 129-139. //doi.org/10.1016/S0021-9258[18]71951-0
Stieber, M. [2014, April 12]. Gene interactions P1 [video file]. YouTube. //www.youtube.com/watch?v=Fv7UtsPfF-A
The phrase "one gene, one protein" is inaccurate, as shown by the example of haemoglobin: this protein contains prosthetic haem groups which are not made by the activity of any gene, therefore genes alone cannot make every protein. "one gene, one enzyme" is also incorrect, because some genes code for proteins such as collagen or elastin, which have a structural role in the body rather than as catalysts in metabolism, so they are not enzymes.
The correct term is "one gene, one polypeptide" as the sequence of codons on any strand of DNA can only code for the assembly of a polypeptide chain with one possible arrangement of amino acid residues following transcription and translation.
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Table of ContentsKey People:George Wells Beadle Edward L. Tatum...[Show more]Related Topics:genetics enzyme gene...[Show more]
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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.