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The "one gene--one enzyme" hypothesis

12/14/2022
Sadie Davenport

In 1958, George Beadle and Edward Tatum won the Nobel Prize for their study on the relationship between genes and enzymes. They proved through the mutation of Neurospora (a bread mold) that individual genes control specific enzymes. This has been summarized as the "one gene--one enzyme" hypothesis, which is now considered too simplified to accurately depict the relationship between genes and enzymes. However, this hypothesis is remembered as the link connecting two important disciplines: genetics and biochemistry. 

 

 

The experiment:

1) Beadle and Tatum grew Neurospora cells in test tubes with a "complete medium."

2) Then they exposed the Neurospora cells to X-rays and placed them in new tubes under the same conditions. 

3) They waited for the cells to divide and grow. 

4) They transferred some of the cells to a "minimal medium" with a nutrient base of sugar, salts, and biotin. 

5) They observed which cells lived and which died. (This meant that some cells couldn't break down the nutrients in the test tube.)

5) They further tested for different metabolic mutations and, with a lot of experiment repetition, found a different gene mutation connected to each metabolic mutation.

There's a lot more to this experiment, so be sure to check out the additional resources below! 

(Diagram from Khan Academy.) 

Read more about the "one gene, one enzyme" hypothesis: 

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Published in: 2022. Baltimore: Johns Hopkins University Press.

Available: As an eBook in our Academic eBook Collection. 

Description: "The focus of bioethical debates on exceptional cases neglects the underlying values—like justice and community—that would lend to a broader, more well-rounded understanding of today's world.Discussions of ethical problems in health care too often concentrate on exceptional cases. Bioethical controversies triggered by experimental drugs, gene-edited babies, or life extension are understandably fascinating: they showcase the power of medical science and technology while addressing anxieties concerning health, disease, suffering, and death. However, the focus on rare individual cases in the media spotlight turns attention away from more pressing ethical issues that impact global populations, such as access to health care, safe food and water, and the prevention of emerging infectious diseases. In Bizarre Bioethics, Henk A.M.J. ten Have argues that this focus on bizarre cases leads to bizarre bioethics with a narrow agenda for ethical debate. In other words, although these extreme cases are undeniably real, they present a limited and skewed view of everyday moral reality. This focus also assumes that individuals are rational decision-makers, so that the role of feelings and emotions can be downgraded. Larger questions related to justice, solidarity, community, meaning, and ambiguity are not appreciated. Such questions used to be posed by philosophical and theological traditions, but they have been exorcised and marginalized in the development of bioethics. Science, ten Have writes, is not a value-free endeavor that provides facts and evidence: it is driven by underlying value perspectives that are often based on metaphors and world views from philosophical and theological traditions. Drawing on a rich analysis of the literature, ten Have explains how bioethical discussion can be enriched by these metaphors and develops a broader approach that critically delves into the imaginative world views that determine understanding of the world and human existence. Examining the roles of the metaphors of ghosts, monsters, pilgrims, prophets, and relics, ten Have illustrates how science and medicine are animated by imaginations that fuel the search for hope, salvation, healing, and a predictable future. Bizarre Bioethics invites students, researchers, policymakers and teachers interested in ethics and health care to think about the value perspectives on health and disease today."

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Making it possible to live with chronic kidney disease (CKD)
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On this day in 1960, for the first time, Dr. Belding Scribner (Scrib) inserted a shunt into a man's arm to connect an artery to a dialysis machine. The operation was successful and enabled the man, Clyde Shields, to survive on dialysis for over a decade. This shunt (shown in the images below) was the last piece of technology needed to provide long-term dialysis for patients with failing kidneys. The impact of this successful procedure was immediate -- kidney failure was no longer a death sentence. 

      

Left: A diagram naming parts of the original 1960 shunt. Middle: The shunt inserted into Clyde Shields's arm in 1960. Right: Dr. Belding Scribner. 

How it works: The shunt consists of two extension tubes, a stabilizer, and a "U tube" (which takes on a U-shape closer to the patient's elbow). When dialysis is needed, the "U tube" is removed and the dialysis machine connected in its place. (The original 1966 article below explains how this shunt works in more detail.)

Today: Now there are more options for dialysis. Patients may undergo surgery to have a fistula or graft in their arm, or a catheter in their neck, all of which improve access to the bloodstream for dialysis. At-home dialysis is also possible. The patient education webpages listed below offer general overviews of dialysis, including its types, steps, effects, risks, and outlooks. 

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Mary Amdur's remarkable story of research ethics
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Left: Mary Amdor. Middle: The deadly fog in Donora, Pennsylvania. Right: Woman walking through the fog in Donora. 

In late October of 1948, a combination of temperature fluctuations and deadly emissions from two U.S. Steel plants created a dense, yellow fog that hung over the city of Donora, Pennsylvania, killing 70 people and injuring 6,000 others. The fog, which contained sulfuric acid, nitrogen dioxide, fluorine, and other poisonous gases, remained in the city for several days until it rained on October 31st. Doctors and firefighters shared bottled oxygen with Donora residents and urged those with pre-existing lung and breathing issues to leave, but the density of the fog made driving and transportation nearly impossible.

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For her work and her strength to stick to her own ethical principles, Dr. Mary Amdur became known as the "mother of air pollution toxicology." And in 1961, the United States adopted the Clean Air Act, which "regulates air emissions from stationary and mobile sources," in order to prevent dangerous air pollution events like Donora's. (Summary of the Clean Air Act). 

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