George Wells Beadle

Geneticist

• Born: October 22, 1903
• Birthplace: Wahoo, Nebraska
• Died: June 9, 1989
• Place of death: Pomona, California

American geneticist

American geneticist George Wells Beadle is best remembered for his Nobel Prize-winning collaboration with Edward Tatum on the one gene-one enzyme hypothesis. Their work revealed that DNA encodes individual proteins and that mutations, or changes in DNA, lead to changes in proteins. Beadle and Tatum laid the foundations for the field of genetic engineering. In 1958, they were awarded the Nobel Prize in Physiology or Medicine.

Born: October 22, 1903; Wahoo, Nebraska

Died: June 9, 1989; Pomona, California

Primary field: Biology

Specialty: Genetics

Early Life

George Wells Beadle was born in Wahoo, Nebraska, on October 22, 1903. His mother died when he was young, leaving his father to care for three children and a forty-acre farm alone. During high school, Beadle’s teachers saw his potential and helped convince his father to send him to college.

Beadle attended the College of Agriculture in Lincoln, Nebraska. He then transferred to the University of Nebraska, where he received his bachelor’s degree in 1926 and his master’s degree a year later. During college, Beadle became interested in crop genetics research. After graduation he entered Cornell University in Ithaca, New York, where he studied the genetics of Zea mays, or corn. He earned his PhD in 1931.

Beadle continued his corn genetics work from 1931 to 1936 at the California Institute of Technology (Caltech), supported by a National Research Council fellowship. There he began investigating the process of crossing-over in the fruit fly, Drosophila melanogaster, under the guidance of the 1933 Nobel Prize winner Thomas Hunt Morgan. Crossing-over is a process that occurs during the formation of gametes (the combination of ova and sperm). Each cell, whether from a fly, a human, or corn, has chromosomes made up of long, coiled molecules of deoxyribonucleic acid (DNA). These chromosomes carry hereditary information from one generation to the next. The cells are diploid, meaning that they have two copies of most of their chromosomes (one from the mother and one from the father).

Crossing-over increases variation in the gene pool by combining chromosomes from maternal and paternal lines. During crossing-over, a small piece of the maternal chromosome breaks off, as does a corresponding region on the paternal chromosome. They switch places and reattach to the opposite chromosome. This creates new combinations of genes not seen in either parent.

Life’s Work

Beadle’s fruit-fly research led him to travel to Paris in 1935 to work with Professor Boris Ephrussi at the Institut de Biologie Physico-Chimique. Together, they investigated the development of eye pigment in Drosophila. Eye pigment is synthesized in a series of biochemical steps, so this work prefigured Beadle’s later exploration of biochemical pathways in Neurospora (bread mold). Beadle left Paris to teach genetics at Harvard University in 1936.

In 1937, George Wells Beadle became a professor of biology at Stanford University. To investigate the genetic regulation of biochemical pathways, he chose a simple organism: the red bread mold Neurospora crassa. Beadle and his colleague Edward Tatum came across some little-known writings by the British doctor Archibald Garrod. In 1901, Garrod had published his idea that genes control the production of proteins. He was correct, but his work received little attention at the time of its publication. Years later, Beadle and Tatum recognized its importance.

Beadle and Tatum designed an experiment to test the idea that DNA encodes individual enzymes. Enzymes are natural catalysts, usually made of proteins, that speed up chemical reactions in cells. If there really were a gene coding for every enzyme, then disrupting the gene should produce an incorrect, and probably nonfunctional, enzyme. Beadle and Tatum used X-rays and ultraviolet radiation to damage the DNA of thousands of Neurospora cultures, resulting in a number of mutated strains of Neurospora. Their method of causing mutations was random; any genes for any traits could be damaged.

After the radiation treatment, Beadle and Tatum screened the cultures, looking for survivors that carried detectable mutations. Some of the cultures showed mutations in genes that coded enzymes used in synthesizing essential nutrients. These mutated cultures lost the ability to live on simple media (food sources) and could only survive if their media was supplemented with essential molecules like thiamine or choline. Neurospora normally has very minimal nutritional requirements; it can live only on sugar supplemented with the vitamin biotin, since it synthesizes other needed nutrients. Beadle and Tatum reasoned that there must be a series of chemical reactions converting available molecules into necessary nutrients. An enzyme made of protein must catalyze, or accelerate, each reaction.

Think of this biochemical pathway as the sequence A ? B ? C ? D. Each letter represents a different kind of molecule in the pathway. The last molecule in line, D, is essential. Only A is available in the media. Making A directly into D is impossible, so a series of steps (the biochemical pathway) is used. Each arrow represents a different chemical reaction that converts one kind of molecule into the next, with a different enzyme catalyzing each reaction. All these enzymes are encoded by different DNA sequences, or genes. Neurospora that has a mutation in the gene for the enzyme that makes B into C can still make A into B. So molecule B, being created but not used up, accumulates. This mutant cannot make its own supply of molecule C. If molecule C were added artificially, the pathway could continue to the end. This is what Beadle and Tatum found in the mutant Neurospora strains. By providing different nutrients to each mutant, they were able to figure out which reaction was blocked in each strain.

Beadle left Stanford in 1946 to join Caltech as professor and chairman of the biology division, remaining there for fifteen years. In 1958, he and Tatum shared half of the Nobel Prize in Physiology or Medicine for their research on the genetic code; molecular biologist Joshua Lederberg won the other half of the prize. Later, Beadle and his second wife, Muriel, wrote a book on genetics entitled The Language of Life, published in 1966. It was one of the first books to explain the concepts of genetics to a nonprofessional audience.

George Beadle’s last position before retirement was as chancellor of the University of Chicago. When he took over, the institution was suffering from declining enrollment and loss of faculty. Under Beadle’s leadership, the university thrived. He persuaded some of the finest professors available to join his faculty, including several Nobel Prize winners. Beadle was one of the first academics to speak out in favor of multicultural education, an idea now embraced by colleges nationwide. He was also concerned about the ethical implications of scientific advancements, especially in the realm of genetics.

Impact

The experiments conducted by Beadle and Tatum provided evidence that enzymes are encoded by DNA. Because of this, scientists eventually discovered that the sequence of nucleotide bases (subunits that make up the larger DNA molecule) in DNA determines the sequence of amino acids in a protein. Amino acids are smaller molecules that link together to make up larger proteins. The concept was originally known as the one gene-one enzyme hypothesis. Later, it became clear that one gene actually codes for one polypeptide chain, a chain of amino acids strung together in a specific order, like beads on a string. A functioning protein might be made up of only one chain, or it might be several chains linked together. This plus the realization that there are many other proteins besides enzymes led to the renaming of the idea as the one gene-one polypeptide hypothesis.

Beadle’s Neurospora research eventually led to large-scale production of the antibiotic penicillin, which is produced by fungal cultures. Penicillin is made naturally by fungi to kill their bacteria, but it can be purified to fight infections in animals and people.

George Wells Beadle was the recipient of more than thirty honorary degrees. His numerous awards include the Albert Einstein Commemorative Award in Science in 1958 and the National Award from the National Cancer Society in 1959. He and his wife Muriel received the 1967 Edison Award for their efforts to make the science of genetics understandable to the general public.

Bibliography

Beadle, George Wells, and Muriel Beadle. The Language of Life: An Introduction to the Science of Genetics. Garden City: Doubleday, 1966. Print. Beadle’s introduction to genetics, cowritten with his second wife.

Berg, Paul, and Maxine Singer. George Beadle: An Uncommon Farmer; The Emergence of Genetics in the 20th Century. Cold Spring Harbor: Cold Spring Harbor Laboratory Press, 2005. Print. A biography of Beadle, set against the backdrop of genetics research in the middle of the twentieth century.

Griffiths, Anthony J. F., et al. Introduction to Genetic Analysis. 10th ed. New York: Freeman, 2010. Print. An introductory text for the study of genetics with an explanation of the one gene-one enzyme theory.