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Section 3:What is Life

Thus a living organism continually increases its entropy -or, as you may say, produces positive entropy -and thus tends to approach the dangerous state of maximum entropy, which is of death. It can only keep aloof from it, i.e. alive, by continually drawing from its environment negative entropy -which is something very positive as we shall immediately see. What an organism feeds upon is negative entropy. Or, to put it less paradoxically, the essential thing in metabolism is that the organism succeeds in freeing itself from all the entropy it cannot help producing while alive.

Schrodinger, What is Life

Max Delbrück (1906-1981)


Max Delbrück, (born Sept. 4, 1906, Berlin, Ger.—died March 9, 1981, Pasadena, Calif., U.S.), German-born U.S. biologist, a pioneer in the study of molecular genetics. With Alfred Day Hershey and Salvador Luria, he was awarded the 1969 Nobel Prize for Physiology or Medicine for work on bacteriophages—viruses that infect bacteria.


Delbrück received a Ph.D. in physics (1930) from the University of Göttingen. His interest in bacteriophages was aroused while he was a research assistant at the Kaiser Wilhelm Institute for Chemistry in Berlin (1932–37). A refugee from Nazi Germany, Delbrück went to the United States in 1937, serving as a faculty member of the California Institute of Technology (1937–39; 1947–81) and of Vanderbilt University (1940–47). He became a U.S. citizen in 1945.


In 1939 Delbrück discovered a one-step process for growing bacteriophages that, after a one-hour latent period, would multiply to produce several hundred thousands of progeny. Delbrück soon began to collaborate with Luria, and in 1943 they announced their discovery that a bacterium that has been infected by a bacteriophage can undergo spontaneous mutations so that it becomes immune to the phage. In 1946 Delbrück and Hershey independently discovered that the genetic material of different kinds of viruses can combine to create new types of viruses. This process was previously believed to be limited to higher, sexually reproducing forms of life.

Salvador Edward Luria (1912-1991)

Salvador Luria, in full Salvador Edward Luria, (born Aug. 13, 1912, Turin, Italy—died Feb. 6, 1991, Lexington, Mass., U.S.), Italian-born American biologist who (with Max Delbrück and Alfred Day Hershey) won the Nobel Prize for Physiology or Medicine in 1969 for research on bacteriophages, viruses that infect bacteria.


Luria graduated from the University of Turin in 1935 and became a radiology specialist. He fled Italy for France in 1938 and went to the United States in 1940 after learning the techniques of phage research at the Pasteur Institute in Paris. Soon after his arrival, he met Delbrück, through whom he became involved with the American Phage Group, an informal scientific organization devoted to solving the problems of viral self-replication. Working with a member of the group in 1942, Luria obtained one of the electron micrographs of phage particles, which confirmed earlier descriptions of them as consisting of a round head and a thin tail. In 1943 Luria and Delbrück published a paper showing that, contrary to the current view, viruses undergo permanent changes in their hereditary material. That same year he and Delbrück devised the fluctuation test, which provided experimental evidence that phage-resistant bacteria were the result of spontaneous mutations rather than a direct response to changes in the environment. In 1945 Hershey and Luria demonstrated the existence not only of such bacterial mutants but also of spontaneous phage mutants.


Luria became Sedgwick professor of biology at the Massachusetts Institute of Technology in 1964. In 1974 he became director of the Center for Cancer Research at MIT. He was an author of a college textbook, General Virology (1953), and a popular text for the general reader, Life: The Unfinished Experiment (1973).


Erwin Schrodinger (1887-1961)


Erwin Schrödinger (born August 12, 1887, Vienna, Austria—died January 4, 1961, Vienna) was a Nobel Prize-winning Austrian physicist whose groundbreaking wave equation changed the face of quantum theory.

Schrödinger was taught at home by private teachers until he was 11 years old, and then attended Vienna's Akademisches Gymnasium. He went on to enter the University of Vienna, where he focused primarily on the study of physics and was strongly influenced by another young physicist, Fritz Hasenöhrl, and graduated with a Ph.D. in physics in 1910. Afterward, he worked for a few years at the institution as an assistant but was drafted into World War I in 1914, serving with Austro-Hungarian military forces in Italy as an artillery officer. Upon returning to civilian life, Schrödinger married Annemarie Bertel in 1920. He also took on a number of faculty/staff positions at places like the University of Stuttgart, the University of Jena and the University of Breslau, before joining the University of Zurich in 1921.

Schrödinger's tenure as a professor at the University of Zurich over the next six years would prove to be one of the most important periods of his physics career. Immersing himself in an array of theoretical physics research, Schrödinger came upon the work of fellow physicist Louis de Broglie in 1925. In his 1924 thesis, de Broglie had proposed a theory of wave mechanics. This sparked Schrödinger's interest in explaining that an electron in an atom would move as a wave. The following year, he wrote a revolutionary paper that highlighted what would be known as the Schrödinger wave equation. He was awarded the 1933 Nobel Prize in Physics, along with British physicist P.A.M. Dirac, and later became a director at Ireland's Institute for Advanced Studies.

In 1944, Schrödinger wrote What Is Life?, an attempt to show how quantum physics can be used to explain the stability of genetic structure. Although much of what Schrödinger had to say in this book has been modified and amplified by later developments in molecular biology, his book remains one of the most useful and profound introductions to the subject.

George Beadle(1903-1989)


George Wells Beadle (October 22, 1903 – June 9, 1989) was an American geneticist. Beadle was born on a farm and studied at the University of Nebraska, where he became interested in ecology. He then entered Cornell University and joined the same lab with Barbara McClintock. After receiving his Ph.D., Beadle worked at California Institute of Technology (Cal-Tech) since 1931, and later succeeded Thomas Morgan as the chairman of the Biology Division. In 1961 Beadle surprised his colleges by accepting the presidency of the University of Chicago. He became a successful administrator and largely increased the faculty before retiring in 1968 at age 65.

Beadle was a talented experimenter and worked on maize, drosophila, and neurospora. He began to work with Edward Tatum (1909-1975) in 1941 and used X-irradiation to induce mutants of Neurospora, which led to “one gene–one enzyme” hypothesis that each gene was responsible for an enzyme that effected the phenotype. Their recognition of gene action in the 1940s preceded Waston and Crick, and Beadle and Tantum won the Nobel Prize in Physiology or Medicine in 1958 for “their discovery that genes act by regulating definite chemical events,” shared with Joshua Lederberg (American molecular biologist, 1925-2008).

Edward Tatum(1909-1975)

Edward Lawrie Tatum (December 14, 1909 – November 5, 1975) was an American geneticist and biochemist, and won the Nobel Prize in 1958 together with George Wells Beadle (1903–1989). Tatum was born to a well-educated family in Colorado as the eldest son of three children. When Tatum was fifteen, his father accepted a position as a pharmacology professor at the University of Wisconsin, where Tatum earned his A.B. in chemistry in 1931 and Ph.D. in biochemistry in 1934. Two years later, Tatum went to the University of Utrecht in the Netherlands to study bacteriological chemistry and connected to George Beadle. They began to work on neurospora in 1941 and provided experimental evidence for one gene – one enzyme theory, and together won the Noble Prize in Physiology or Medicine in 1958. Tatum and Beadle’s experiment on neurospora helped to produce large amounts of penicillin during World War II. 


After the war, Tatum taught at Yale University, Stanford University, and finally took a position at the Rockefeller Institute for Medical Research (now Rockefeller University) in 1957. In addition to collaborating with Beadle, Tatum also worked with Joshua Lederberg (1925-2008) when he was at Yale in 1946 and proved that the bacterium Escherichia coli reproduced sexually - when two different kinds of mutant were put together, a third new strain resulted, which Tatum called genetic recombination.


Oswald Theodore Avery Jr. (1877-1955)


Oswald Avery, in full Oswald Theodore Avery, (born October 21, 1877, Halifax, Nova Scotia, Canada—died February 20, 1955, Nashville, Tennessee, U.S.), Canadian-born American bacteriologist whose research helped ascertain that DNA is the substance responsible for heredity, thus laying the foundation for the new science of molecular genetics. His work also contributed to the understanding of the chemistry of immunological processes.


Avery received a medical degree from Columbia University College of Physicians and Surgeons in New York City in 1904. After a few years in clinical practice, he joined the Hoagland Laboratory in Brooklyn and turned his attention to bacteriological research. In 1913 he joined the staff of the Rockefeller Institute Hospital in New York City. Based on the recognition that the polysaccharide composition of capsular envelopes can vary, Avery helped classify pneumococci into different types. Avery also found that the polysaccharide could stimulate an immune response—specifically, the production of antibodies—and was the first to demonstrate that a substance other than a protein could do so. 

In 1932 Avery turned his attention to an experiment carried out by a British microbiologist named Frederick Griffith. Avery, along with many other scientists, set out to determine the chemical nature of the substance that allowed transformation to occur. In 1944 he and his colleagues Maclyn McCarty and Colin MacLeod reported that the transforming substance—the genetic material of the cell—was DNA. This result was met initially with skepticism, as many scientists believed that proteins would prove to be the repository of hereditary information. Eventually, however, the role of DNA was proved, and Avery’s contribution to genetics was recognized.

Maclyn McCarty (1911-2005)

Maclyn McCarty, (born June 9, 1911, South Bend, Indiana, U.S.—died January 2, 2005, New York, New York), American biologist who, with Oswald Avery and Colin M. MacLeod, provided the first experimental evidence that the genetic material of living cells is composed of deoxyribonucleic acid (DNA).


McCarty attended Stanford University (B.S., 1933) and Johns Hopkins School of Medicine (M.D., 1937) before joining William S. Tillett at New York University in 1940. Tillett not only introduced McCarty to the study of pneumococcic bacteria but also arranged for him to work with Avery in his laboratory at the Rockefeller Institute (now Rockefeller University) in New York City. McCarty became a member of the institute in 1950 and later served as its vice president (1965–78). From 1960 to 1974 he was physician in chief at the school’s hospital. He also chaired New York City’s Public Health Research Institute (1985–92).


Colin Munro MacLeod (1909-1972)


Colin Munro MacLeod (January 28, 1909 -- February 11, 1972) was a Canadian-American geneticist who along with Oswald Avery and Maclyn McCarty, proved that DNA is the molecule responsible for the transformation of pneumoniae. Their research makes contribution to proving that DNA is the carrier of genetic information. Colin's mother was a teacher and his father was a Presbyterian minister in Scotland. After skipping three grades in elementary school, he enrolled at McGill University at 16 and earned his M.D. at 23.

At an early age, Macleod, and Avery and McCarty completed the vitro transformation experiments for Diplococcus pneumoniae, proving that DNA is the factor who contributes to the transformation. The experiment is also known as “Avery - Macleod - McCarty Experiment”. On the basis of them, a series of experiments proved that the DNA is the main genetic material. In 1941, he was appointed chairman of the Department of Microbiology at New York University School of Medicine. Later, he served on the Army Epidemiology Board, the National Institutes of Health, and was elected a member of the National Academy of Sciences. Later, he mainly assisted the Southeast Asian Treaty Organization to research approaches to solving cholera.

Avery-MacLeod-McCarty Experiment in 1944

On February 1, 1944, physician and medical researcher Oswald Avery together with his colleagues Colin MacLeod and Maclyn McCarty announced that DNA is the hereditary agent in a virus that would transform a virus from a harmless to a pathogenic version. This study was a key work in modern bacteriology.

The achievement by the scientists Avery, MacLeod, and McCarty were based on Frederick Griffith’s studies on bacteria. Avery and his collaborators Colin MacLeod and Maclyn McCarty at Rockefeller University (then Rockefeller Institute) in New York wanted to elucidate the chemical nature of the transforming substance.


They refined the purification process until the result was a cell extract whose amounts of carbon, hydrogen, nitrogen and phosphorus corresponded to those of DNA. To ensure that the transformation was not induced by residues of RNA or proteins, they treated the cell extract with different enzymes prior to the transformation. One of these enzymes had a deoxyribonucleode polymerase activity described by Greenstein in 1940. Only this neutralized the transformation activity of the extract, while trypsin, chymotrypsin (two protein cleaving enzymes), ribonuclease, protein phosphatases and esterase had no effect on transformation activity. They were also able to show that all offspring inherited the S-properties and that the repetition of the experiment with extracts from these offspring led to the same results.

Alfred Hershey (1908-1997) 


Alfred Day Hershey (December 4, 1908 – May 22, 1997) was a bacteriologist and geneticist.He received his B.S. in chemistry at Michigan State University in 1930 and his Ph.D. in bacteriology in 1934, taking a position shortly thereafter at the Department of Bacteriology at Washington University in St. Louis.

He began performing experiments with bacteriophages with Salvador Luria, Max Delbrück, and observed that when two different strains of bacteriophage have infected the same bacteria, the two viruses may exchange genetic information.

In 1950, he joined the Carnegie Institution of Washington's Department of Genetics, where he and Martha Chase performed the famous Hershey–Chase experiment in 1952.  This experiment provided additional evidence that DNA, not protein, was the genetic material of life. He became director of the Carnegie Institution (which later became Cold Spring Harbor Laboratory) in 1962 and was awarded the Nobel Prize in Physiology or Medicine in 1969, shared with Salvador Luria and Max Delbrück for their discovery on the replication of viruses and their genetic structure.

Martha Chase (1927-2003)

Martha Cowles Chase (November 30, 1927 – August 8, 2003), also known as Martha C. Epstein, was an American geneticist who in 1952, with Alfred Hershey, experimentally helped to confirm that DNA rather than protein is the genetic material of life. Chase received a bachelor's degree from the College of Wooster in 1950. And then received a PhD in Microbiology from the University of Southern California in 1964. In 1950, Chase began working as a research assistant at Cold Spring Harbor Laboratory in the laboratory of Alfred Hershey.


Hershey and Chase Experiment in 1952

In the early twentieth century, it was an issue whether genes were chemically DNA or protein. In 1951 and 1952, Alfred Hershey and Martha Chase performed a series of experiments at the Carnegie Institute of Washington in Cold Spring Harbor, New York. They clarified that genes were made of DNA rather than protein. Their experiments are also known as the Hershey-Chase experiments.

Hershey and Chase took advantage of a technique called radioactive isotope labeling. The first Hershey-Chase experiment aimed to confirm previous experimental findings that the DNA and protein components of phages were separable. Hershey and Chase replicated Thomas Anderson’s experimental results using their radioactive isotope labeling method. Showing that phages consisted of a protein shell, or coat, with DNA inside the shell, and the phages could release their DNA and leave behind their protein coats. Then in another Hershey-Chase experiment, Hershey and Chase showed that when certain phages infected E. Coli, the phages injected their DNA into the host bacterium.

The most well-known Hershey-Chase experiment was the final experiment, which is also called the Waring Blender experiment. Hershey and Chase showed that phages only injected their DNA into host bacteria, and that the DNA served as the replicating genetic element of phages. For their experiment, Hershey and Chase prepared two samples of E. Coli. They infected one sample with radioactive phosphorus-labeled phages, and the other sample with radioactive sulfur-labeled phages. Then, they stirred the two samples each in a Waring Blender. In the phosphorus-labeled sample that marked DNA but not protein, the blender removed forty percent of the labeled particles. In the sulfur-labeled sample that marked protein but not DNA, the blender removed eighty percent of the labeled particles. Those results suggested that the blender removed much more of the protein parts of the phage than the DNA parts, which indicated that the protein likely remained outside of the cell during infection. The protein could not be the replicating genetic material, for the protein had never entered into the cell.

Coleman Model 3D pH Meter, 1938

Self contained pH meter with wooden exterior; hinged top door opens to reveal meter face and inlaid paper instructions for use; the double scale reads pH and millivolts; hinged door on left side of wooden case opens to reveal electrode compartment.

Science History Institute. Coleman Model 3D PH Meter. Photograph, 2016.

Science History Institute. Philadelphia. 


Coleman Model 3D pH Meter, 1938

Beckman Instruments. “Beckman PH Meter (Industrial Model) Brochure,” 1935–1940.
Beckman Historical Collection, Box 20, Folder 2. Science History Institute. Philadelphia. 


Beckman Model G Glass Electrode pH Meter,1950

Self-contained pH meter with wooden exterior; hinged top door opens to reveal meter face and inlaid paper instructions for use;

the dial is calibrated from pH 0 to pH 13 in .1 pH divisions; porcelain enamel-lined electrode compartment at front of pH meter.
Designed for precise measurements in the laboratory but also suitable for field and factory use. With combination pH and millivolt scale, permitting both pH determinations and oxidation-reduction potential measurements,

new type glass and calomel electrodes and lock-down switch.

Portable, self-contained, direct reading instrument suitable for practically all substances.
Science History Institute. Beckman Model G Glass Electrode PH Meter. Photograph, 2016. Science History Institute. Philadelphia.


Beckman Model G pH meter in use,1955

Arnold Beckman invented his first pH meter in 1934 at the request of a chemist from the California citrus industry, who needed an accurate way to measure the acidity of his product. The resulting “acidimeter” with its glass electrode was renamed the Model G pH meter in 1937 and produced on a larger scale by Beckman’s company, National Technical Laboratories. This instrument kicked off the rapid development not only of NTL and Beckman Instruments but also of the electronic scientific instrument industry.
“Beckman Model G PH Meter in Use,” circa 1955. Beckman Historical Collection, Box 55, Folder 74. Science History Institute. Philadelphia.

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