what was the blender experiment

Hershey and Chase Experiment

Hershey and Chase experiment give practical evidence in the year 1952 of DNA as genetic material using radioactive bacteriophage . Griffith also explained the transformation in bacteria and concluded that the protein factor imparts virulence to the rough strain, but it was not proved to be genetic material.

Avery , Macleod and McCarthy further studied the Griffith experiment and concluded that the DNA was the genetic material responsible for transforming the avirulent rough strain to the virulent strain. To resolve the query of genetic material, many researchers were engaged to know whether the cause of inheritance is protein or DNA.

Many assessments then led to the discovery of “ DNA ” as genetic material or the cause of inheritance . One of the best experiments that provide DNA evidence as genetic material is the “ Hershey and Chase experiment ”. We will study the definition, steps (radioactive labelling, infection, blending and centrifugation) and observation of the Hershey and Chase experiment in this context.

Content: Hershey and Chase Experiment

Radioactive labelling of bacteriophage, centrifugation, observation, definition of hershey and chase experiment.

Hershey and Chase’s experiment has demonstrated the DNA is the genetic material where they have taken the radioactive T2-bacteriophage (Viruses that infect E.coli bacteria). T2-bacteriophage or Enterobacteria phage T2 belongs to the Group-I bacteriophage.

Video: Hershey and Chase Experiment

Hershey and Chase Experiment Steps

Hershey and Chase gave full evidence of the DNA being a genetic material by their experiments. To perform the experiment, Hershey and Chase have taken T-2 bacteriophages (invaders of E.coli bacteria). The experiment includes the following steps:

Hershey and Chase have grown T-2 bacteriophages in the two batches. In batch-1, we need to grow the bacteriophages in the medium containing radioactive sulphur (S 35 ) and radioactive phosphorus (P 32 )  in batch-2. After incubation, we could see that the radioactive sulphur (S 35 ) will tag the phage protein. The radioactive phosphorus (P 32 ) will tag the phage DNA.

After radioactive labelling of the phage DNA and protein, Hershey and Chase infected the bacteria, i.e. E.coli by using the radioactively labelled T-2 phage. In batch-1, T-2 phage tagged with S 35 and in batch-2 T-2 phage labelled with P 32 were allowed to infect the bacterial cells of E.coli .

After the attachment of  T-2 bacteriophage to the E.coli , the phage DNA will enter the cytoplasm of E.coli . The phage DNA will take up the host cell machinery. Degradation of the bacterial genome occurs by the T2-phages where they use the ribosomes to form structural proteins of the capsid, tail fibres, base plate etc.

At the time of blending or agitation, the bacterial cells are agitated to remove the viral coats . As a result of the agitation, we get a solution containing bacterial cells and viral particles like capsid, tail fibres, base plate, DNA etc.

After the centrifugation, we could observe the results to identify the heritable factor . The phage DNA labelled with P 32  will transfer the radioactivity in the host cell. Thus, the radioactive P 32  enters a bacterial cell and exists in the form of “Pellets”. The phage protein tagged with S 35 will not transfer its radioactivity in the host cell. As a result, radioactive S 35 will appear in the form of  “Supernatant” in the solution.

The P 32 labelled phage DNA will transfer its radioactivity to the host cell DNA, while S 35 labelled phage protein will not do so. The P 32 labelled phage DNA will remain inside the E.coli cell even after blending and centrifugation. According to the Hershey and Chase experiment, we can conclude that the DNA is the genetic material because the P 32 tagged T2-phage DNA will transfer the radioactivity to the host cell ( E.coli ) not the S 35 labelled T2-phage protein.

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A.D. Hershey

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A.D. Hershey (born Dec. 4, 1908, Owosso, Mich., U.S.—died May 22, 1997, Syosset, N.Y.) was an American biologist who, along with Max Delbrück and Salvador Luria , won the Nobel Prize for Physiology or Medicine in 1969. The prize was given for research done on bacteriophages (viruses that infect bacteria).

Hershey earned a doctorate in chemistry from Michigan State College (now Michigan State University) in 1934 and then took a position at Washington University School of Medicine in St. Louis, Mo. He joined the staff of the Genetics Research Unit of the Carnegie Institution of Washington in 1950 after giving up his position as professor at Washington University. In 1963 he became director of the Genetics Research Unit.

Hershey, Delbrück, and Luria began exchanging information on phage research in the early 1940s. In 1945 Hershey and Luria, working independently, demonstrated the occurrence of spontaneous mutation in both the bacteriophages and the host. The next year, Hershey and Delbrück independently discovered the occurrence of genetic recombination in phages— i.e., that different strains of phages inhabiting the same bacterial cell can exchange or combine genetic material. Delbrück incorrectly interpreted his results as specifically induced mutations, but Hershey and one of his students proved that the results they had obtained were recombinations by showing that the genetic processes in question correspond with the crossing-over of parts of similar chromosomes observed in cells of higher organisms.

Hershey is most noted for the so-called blender experiment that he performed with Martha Chase in 1952. By showing that phage DNA is the principal component entering the host cell during infection, Hershey proved that DNA, rather than protein, is the genetic material of the phage.

In 1951 and 1952, Alfred Hershey and Martha Chase conducted a series of experiments at the Carnegie Institute of Washington in Cold Spring Harbor, New York, that verified genes were made of deoxyribonucleic acid, or DNA. Hershey and Chase performed …

In 1951 and 1952, Alfred Hershey and Martha Chase conducted a series of experiments at the Carnegie Institute of Washington in Cold Spring Harbor, New York, that verified genes were made of deoxyribonucleic acid, or DNA. Hershey and Chase performed their experiments, later named the Hershey-Chase experiments, on viruses that infect bacteria, also called bacteriophages. The experiments followed decades of scientists’ skepticism about whether genetic material was composed of protein or DNA. The most well-known Hershey-Chase experiment, called the Waring Blender experiment, provided concrete evidence that genes were made of DNA. The Hershey-Chase experiments settled the long-standing debate about the composition of genes, thereby allowing scientists to investigate the molecular mechanisms by which genes function in organisms.

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Blending history and science

In 1952, Cold Spring Harbor Laboratory (CSHL) was the site for one of the most famous experiments in the history of biology. At the Animal House—later renamed in honor of Nobel laureate Barbara McClintock— Alfred Hershey and Martha Chase were working with viruses called bacteriophages. The pair sought to confirm whether genes were made of DNA or protein. Their tool of choice? A Waring ® -brand kitchen blender.

Although research in 1944 had shown DNA was the molecule of heredity, the question remained far from settled. Nearly a decade later, the Hershey-Chase, or “Waring Blender,” experiment removed all doubt. Genes are made of DNA . The work would help earn Hershey a share of the 1969 Nobel Prize in Physiology or Medicine with Max Delbrück and Salvador Luria.

In 1979, CSHL honored Hershey by dedicating a new building to the then-retired scientist. Today, the Alfred D. Hershey building is home to several arms of CSHL. These include the Meetings & Courses Program , Flow Cytometry and Microscopy Shared Resources, and Office of Diversity, Equity, & Inclusion .

At the building’s 2012 rededication, CSHL President and CEO Bruce Stillman spoke to Hershey’s continuing legacy . “The propagation of the latest techniques, technologies, and lab methods is central to the success of biology for scientists everywhere, at every stage of career development.”

And yet another critical piece of that legacy is this simple piece of kitchenware.

Nobel laureate Alfred Hershey discusses the Hershey-Chase experiment in a 1991 recording. Hershey served as the director of the Carnegie Institution of Washington Department of Genetics, a predecessor of modern-day CSHL, from 1962 until his retirement in the early ’70s.

Written by : Nick Wurm , Communications Specialist | [email protected] | 516-367-5940

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Alfred D. Hershey, Ph.D.

 Brief Bio

Alfred Day Hershey was born on December 4, 1908, in Owosso, Michigan. He attended Michigan State College, where he earned his B.S. in 1930 and his Ph.D. in bacteriology in 1934. His doctoral dissertation examined the chemical makeup of  Brucella , the bacterium responsible for brucellosis. After completing his degree, Hershey accepted a position as an instructor of bacteriology and immunology at Washington University School of Medicine in St. Louis, where he worked closely with department head Jacques Bronfenbrenner (AAI '20, president 1942–46). Since the early 1920s, Bronfenbrenner had focused his research on the physical and lysogenic properties of bacteriophages, and he encouraged his new faculty member to begin studying the viruses. During the late 1930s, Hershey and Bronfenbrenner studied the growth of bacterial cultures, but his own experiments in the early 1940s focused on the phage-antiphage immunologic reaction and other factors that influenced phage infectivity. Looking back over them 60 years later, Stahl wrote that these studies "appear original, thoughtful, and quantitative, especially those on the use of phage inactivation to permit the study of the antigen-antibody reaction at 'infinite' dilution of antigen."

In late January 1943, Delbrück invited Hershey to Nashville to discuss his phage experiments with him and his close friend Luria. Together, the three formed the nucleus of the "phage group," an informal network of the growing number of scientists devoted to studying the bacteriophage. In 1946, Hershey and Delbrück, working independently, found that different strains of bacteriophage can exchange genetic material when both have infected the same bacterial cell, creating a bacteriophage that is a hybrid of the two, a process Hershey referred to as genetic recombination. By the mid-1940s, Hershey's research with bacteriophage began to shift away from immunology to genetics, biochemistry, and molecular biology.

In 1950, Hershey became a staff member in the Department of Genetics of the Carnegie Institution of Washington at the Cold Spring Harbor Laboratory on Long Island. It was here that he and Chase conducted the blender experiment. In 1962, Hershey was named head of the Genetics Research Unit at Cold Spring Harbor, a position he held until his retirement in 1972.

Hershey died on May 22, 1997, in Syosset, New York, at the age of 88.

 Nobel Prize in Physiology or Medicine

 lasker award,  aai service history,  nobel prize in science.

Alfred D. Hershey was awarded the 1969 Nobel Prize in Physiology or Medicine jointly with Max Delbrück and Salvador E. Luria (AAI '58) for "their discoveries concerning the replication mechanism and the genetic structure of viruses." As leading figures in the study of viruses that infect bacteria, known as bacteriophage, Hershey, Delbrück, and Luria pioneered the fields of microbiology and genetics. Hershey's unique contribution was the discovery that DNA, and not protein, was the genetic material in bacteriophage, a discovery based on evidence from the legendary "blender experiment" undertaken with Martha Chase in 1952.

Bacteriophages were known to be comprised of DNA and protein, and Hershey wanted to determine which of these components was the heritable material passed on to bacteria to form bacteriophage progeny. To trace each of these components separately, Hershey and Chase first prepared one batch of bacteriophage with radioactive phosphorus to label DNA and another with radioactive sulfur to label protein. They then infected different bacterial batches with each of these labeled bacteriophages. Using a Waring blender to shear off the surface-attached bacteriophage from infected bacteria, they were able to analyze the radioactive content of the bacteria and identify the transferred genetic material.

Infected bacteria contained radioactive phosphorus and were also capable of producing bacteriophage progeny, whereas radioactive sulfur was not associated with the bacterial DNA. These results indicated that DNA was transferred from the bacteriophage to the bacteria and that the genetic material in bacteriophage is DNA. These observations enabled Hershey and Chase to confirm that DNA, and not protein, contained genetic information.

Hershey next turned his attention to understanding the infection cycle of bacteriophage at a molecular level and was the first to detect a unique nucleic acid fraction that was later identified as messenger RNA. The consummate experimenter, Hershey continued to develop new laboratory methods for handling, fractioning, and measuring DNA. "There is nothing more satisfying to me than developing a method," he once told a colleague. "Ideas come and go, but a method lasts."

Hershey was renowned for his ingenuity in the lab and was praised by molecular biologist and geneticist Franklin W. Stahl, among other titans, for being "fearless" in the laboratory and "impeccable" in analysis. Stahl lauded Hershey for his humility and absence of pretension: "He talked to the reader, explaining things as he saw them, but never letting us forget that he was transmitting provisional understanding. We got no free rides, no revealed truths, no invitation to surrender our own judgment. And we could never skim, since every word was important. I think this style reflected his verbal reticence, which in turn mirrored his modesty."

 Awards and Honors

• Albert Lasker Basic Medical Research Award , 1958
• Member, National Academy of Sciences, 1958
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• Kimber Genetics Award, 1965
• Nobel Prize in Physiology or Medicine , 1969

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Hershey, Chase and the blender experiment

The hershey-chase experiment, more popularly known as the blender experiment, came at a critical period in the history of modern genetics and marked the beginning of molecular biology as a branch of science. for, this experiment, the results of which were published on september 20, 1952, demonstrated that it was dna, not protein, that transmitted the genetic material of life. a.s.ganesh takes a look at this famous experiment and what came off it....

Updated - November 10, 2021 12:16 pm IST

Overview of the experiment performed by Hershey and Chase, showing DNA to be the genetic material for phage.

Often, during conversations pertaining to heredity, be it with respect to certain mannerisms or behaviour, you might have heard people allude to their DNA. This is because we now know that deoxyribonucleic acid, or DNA, holds the key to heredity to all forms of life and carries genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.

First isolated by Swiss physician Friedrich Miescher in 1869, DNA’s role as the carrier of life’s hereditary data wasn’t known for nearly a century. For, it was only in 1952 that it was firmly established that DNA was the substance that transmits genetic information. That was done through the Hershey-Chase experiment, also often referred to as the blender experiment.

Born in Michigan, the U.S. in 1908, Alfred Day Hershey attended public schools before going on to study B.S. in Bacteriology and doing a Ph.D. in Chemistry. He was drawn towards bacteriology and the biochemistry of life as a graduate student and even his doctoral thesis was on the chemistry of a bacteria. After receiving his Ph.D., Hershey moved into a career of research and teaching.

DNA or protein?

The foundation for the field of molecular biology was laid in the 1940s and the 1950s through research on bacteriophages. Bacteriophages, or simply phages, were known to be viruses – consisting only of DNA surrounded by a protein shell – that infect bacteria.

One of the key questions that was haunting the field was to find out which was the genetic material. The prevalent notion at the time was that it must be a protein, as its structure was complex enough to hold such data. Even though there was some research that pointed at DNA as the possible genetic material, most chemists, physicists and geneticists still held on to the then popular assumption.

Hershey, whose research on phages had provided him with a number of discoveries, set out to conclusively prove that the genetic material in phages was DNA. Along with his assistant Martha Chase, who had recently graduated, Hershey found a way to figure out the role played in replication by each of the phage components.

In experiments conducted in 1951-52, Hershey and Chase used radioactive phosphorus to tag the phage DNA and radioactive sulphur to tag the protein. These tagged phages were then allowed to infect a bacterial culture and begin the process of replication.

Role of blender

This process was interrupted at a crucial moment when the scientists whirled the culture in a blender. This was because Hershey and Chase had been able to determine that a blender produced the right shearing force to tear the phage particles from the bacterial walls, without damaging the bacteria.

Upon examination, it was clear that while the phage DNA had entered the bacterium and forced it to replicate phage particles, the phage protein was still outside, attached to the cell wall. In short, they were able to show that it was DNA, and not protein, that was responsible for communicating genetic information necessary for producing the next generation of phages.

Stimulates research

Hershey and Chase published their results on September 20, 1952. The Hershey-Chase experiment came to be popularly referred to as the blender experiment because of the fact that a simple blender had been used to achieve their test results.

These results stimulated research into DNA, and within months, molecular biologists James Watson and Francis Crick published their work establishing the double helix structure of the DNA molecule. In fact, Watson wrote in a 1997 memoriam that the Hershey-Chase experiment “made me ever more certain that finding the three-dimensional structure of DNA was biology’s next important objective”. It certainly turned out to be right.

Small in size, big prize

Alfred Hershey shared the Nobel Prize in Physiology or Medicine in 1969 with Max Delbruck, a physicist who did research in the U.S. after fleeing Nazi Germany in 1937, and Salvador Edward Luria, a biologist and physician from Italy who fled to France in 1938 and immigrated to the U.S. in 1940. They received the Nobel Prize for their contributions to molecular biology and their work on bacteriophages, which are viruses that infect bacteria.

Working independently, Hershey and Luria showed the occurrence of spontaneous mutation in bacteriophages and the host in 1945.

In the next year, Hershey and Delbruck separately discovered the occurrence of genetic recombination in phages. This showed that when different strains of phages infect the same bacterial cell, they can exchange or combine genetic material.

The three men turned out to be collaborators, despite the fact that they never worked together in the same laboratory.

They encouraged each other in their phage research by sharing results through correspondence and conversations.

Published - September 20, 2019 11:54 pm IST

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• Biology Article
• Dna Genetic Material

DNA As Genetic Material - Hershey And Chase Experiment

Even though researchers discovered that the factor responsible for the inheritance of traits comes from within the organisms; they failed to identify the hereditary material. The chromosomal components were isolated but the material which is responsible for inheritance remained unanswered. Griffith’s experiment was a stepping stone for the discovery of genetic material. It took a long time for the acceptance of DNA as genetic material. Let’s go through the discovery of DNA as genetic material.

Experiments of Hershey and Chase

We know about Griffith’s experiment and experiments that followed to discover the hereditary material in organisms. Based on Griffith’s experiment, Avery and his team isolated DNA and proved DNA to be the genetic material. But it was not accepted by all until Hershey and Chase published their experimental results.

In 1952, Alfred Hershey and Martha Chase took an effort to find the genetic material in organisms.  Their experiments led to an unequivocal proof to DNA as genetic material. Bacteriophages (viruses that affect bacteria) were the key element for Hershey and Chase experiment.

The virus doesn’t have their own mechanism of reproduction but they depend on a host for the same. Once they attach to the host cell, their genetic material is transferred to the host. Here in case of bacteriophages, bacteria are their host. The infected bacteria are manipulated by the bacteriophages such that bacterial cells start to replicate the viral genetic material. Hershey and Chase conducted an experiment to discover whether it was protein or DNA that acted as the genetic material that entered the bacteria.

DNA as Genetic Material

Experiment: The experiment began with the culturing of viruses in two types of medium. One set of viruses (A) was cultured in a medium of radioactive phosphorus whereas another set (B) was cultured in a medium of radioactive sulfur. They observed that the first set of viruses (A) consisted of radioactive DNA but not radioactive proteins . This is because DNA is a phosphorus-based compound while protein is not. The latter set of viruses (B) consisted of radioactive protein but not radioactive DNA.

The host for infection was E.coli bacteria. The viruses were allowed to infect bacteria by removing the viral coats through a number of blending and centrifugation.

Observation:  E.coli bacteria which were infected by radioactive DNA viruses (A) were radioactive but the ones that were infected by radioactive protein viruses (B) were non-radioactive.

Conclusion: Resultant radioactive and non-radioactive bacteria infer that the viruses that had radioactive DNA transferred their DNA to the bacteria but viruses that had radioactive protein didn’t get transferred to the bacteria. Hence, DNA is the genetic material and not the protein.

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• Published: January 2001

Hershey heaven

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We can sleep later: Alfred D. Hershey and the origins of molecular biology

• Franklin W. Stahl

When Alan Garen asked Alfred Hershey for his idea of scientific happiness, Hershey replied, “To have one experiment that works, and keep doing it all the time” 1 . The first generation of molecular biologists referred to this as “Hershey heaven.” Both Hershey's wit and his scientific achievements receive their due in We can sleep later: Alfred D. Hershey and the origins of molecular biology . This volume, edited by Franklin Stahl, pays tribute to Hershey through essays and reminiscences by scientists who knew him and includes a selection of his writings. The recognition, as several contributors point out, is long overdue.

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As quoted in Judson, H.F. The eighth day of creation: The makers of the revolution in biology , 275 (Simon and Schuster, New York; 1979).

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Martha Chase

A: Syosset, New York, United States

Alfred Hershey & Martha Chase Conduct the "Waring Blender Experiment"

Alfred Hershey in 1953

In the early twentieth century biologists thought that proteins carried genetic information. This was based on the belief that proteins were more complex than DNA. In 1928 Frederick Griffith's research suggested that bacteria are capable of transferring genetic information through a process known as  transformation . Research by Avery, MacLeod, and McCarty communicated in 1944  isolated DNA as the material that communicated this genetic information . 

The  Hershey–Chase experiment , often called the "Waring Blender experiment," was conducted in 1952 by American bacteriologist and geneticist  Alfred D. Hershey  and his research partner American geneticist  Martha Chase  at Cold Spring Harbor Laboratory , New York. The experiment showed that when  bacteriophages , which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not , confirming that DNA is the hereditary material.

Hershey & Chase, " Independent Functions of Viral Protein and Nucleic Acid in Growth of Bacteriophage ," J. Gen. Physiol.   36 (1952) 39-56.

Judson, The Eighth Day of Creation, 108. J. Norman (ed) Morton's Medical Bibliography 5th edition (1991) no. 256.

Timeline Themes

Alfred Day Hershey (1908–1997)

During the twentieth century in the United States, Alfred Day Hershey studied phages, or viruses that infect bacteria, and experimentally verified that genes were made of deoxyribonucleic acid, or DNA. Genes are molecular, heritable instructions for how an organism develops. When Hershey started to study phages, scientists did not know if phages contained genes, or whether genes were made of DNA or protein. In 1952, Hershey and his research assistant, Martha Chase, conducted phage experiments that convinced scientists that genes were made of DNA. For his work with phages, Hershey shared the 1969 Nobel Prize in Physiology or Medicine with Max Delbrück and Salvador Luria. Hershey conducted experiments with results that connected DNA to the function of genes, thereby changing the way scientists studied molecular biology and the development of organisms.

Hershey was born on 4 December 1908 to Alma Wilbur and Robert Hershey in Owosso, Michigan. He attended public schools in both Owosso and Lansing, Michigan, where his father worked as a stockkeeper at an automobile factory. For his higher education, Hershey attended Michigan State College, later called Michigan State University, in East Lansing, Michigan. There, he received his Bachelor’s of Science in chemistry in 1930 and his PhD in bacteriology and chemistry in 1934. Hershey wrote his doctoral dissertation on the separation of chemical constituents, or components like sugars, fats, and proteins, from different strains of the Brucella bacterial group. Through that work, Hershey showed how researchers could distinguish between different bacterial types based on the ratio of different chemical components within those types.

In 1934, Hershey joined the faculty at Washington University in St. Louis in St. Louis, Missouri, as an instructor in the bacteriology and immunology department. Starting in 1936, Hershey collaborated with researcher Jacques Bronfenbrenner, the head of the department. From 1936 to 1939, Hershey and Bronfenbrenner primarily studied different conditions that affected the growth rate of bacteria grown in the laboratory. In the early and mid-1940s, the two scientists started to study phages, or viruses that infect bacteria. Specifically, Hershey and Bronfenbrenner studied how bacteria’s immune systems responded to phages.

According to historians, collaboration with Bronfenbrenner shaped Hershey’s early work. Biographers of the researcher Max Delbrück, a prominent phage researcher at Vanderbilt University in Nashville, Tennessee, wrote that Hershey designed his experiments during the early 1940s to support Bronfenbrenner’s description of phages. Bronfenbrenner argued that phages were small protein molecules. At the time, some scientists had observed that phages appeared to be large molecules. To support Bronfenbrenner’s view, Hershey attempted to explain why other scientists observed phages to be large by demonstrating that large particles absorbed smaller phage particles. Scientists later found that phages are large molecules which can contain both protein and nucleic acid, including DNA.

In addition to investigating phages in the early 1940s, Hershey helped establish the Phage Group, an association of scientists who conducted standardized research on phages and attended yearly meetings and courses to advance the field. In the early 1940s, Hershey began communicating with Delbrück. After receiving an invitation from Delbrück, Hershey presented his research on immune responses to phages at Vanderbilt in January 1943. In April 1943, Hershey invited Delbrück and Salvador Luria, Delbrück’s collaborator, to St. Louis to discuss their phage research. Scientists and historians consider these meetings to be the beginning of the Phage Group.

Starting in the 1940s, Hershey began communicating with Delbrück. In a letter sent to Delbrück in October 1943, Hershey wrote about his frustrations with his phage research. Hershey’s frustrations were related to his efforts to support Bronfenbrenner’s small particle view of phages, a view that Delbrück did not support. According to Delbrück biographers, he eventually convinced Hershey to forsake Bronfenbrenner’s theory about phages. Hershey later expressed that he appreciated Delbrück’s support. In 1945, Hershey married Harriet Davidson. The two had a son named Peter in 1956.

Hershey first published his major findings about two types of phages called T2 and T4 in 1946 and 1947. Scientists knew that when phages infect bacteria, those phages replicate and eventually cause bacteria to burst. When the infected bacteria burst, they leave behind plaques, or dark spots, in the places they used to grow. Hershey made multiple observations about how phages infect bacteria by studying plaque formation, and those observations served as evidence for the idea that phages contain genes. Hershey reported changes in the ways that plaques formed and asserted that those changes were caused by a change or mutation in the phages. Hershey also found that when he infected bacteria with two different types of phages, hybrid phages of both types formed. That observation revealed that the phages somehow exchanged genetic materials. Hershey showed that, like other organisms, phages contained genes. That discovery gave scientists a new way to study genetics through phages. Hershey continued to characterize genetic recombination, or the exchange of genetic materials, between phages throughout the rest of the 1940s.

In 1950, Hershey moved his research to the Carnegie Institution of Washington Department of Genetics in Cold Spring Harbor, New York. In 1951, he ended his investigation into genetic recombination in phages. That same year, Chase, a geneticist, joined Hershey’s lab as a research assistant. Hershey and Chase began to research the chemistry of the genetic properties of phages.

Despite Hershey and others’ extensive study of genetic phenomena in phages, scientists in 1951 did not agree about which substances governed the genetic properties of phages. At the time, scientists debated whether genes were made of protein or DNA. In 1944, Oswald Avery and his research group at the Rockefeller Institute in New York City, New York, published experimental findings that supported the theory that genes were made of DNA. However, the experiments failed to convince all scientists. Even in the 1950s, some scientists continued to assert that genes must be made of protein and not DNA.

From 1951 to 1952, Hershey and Chase conducted a series of experiments, later called the Hershey-Chase experiments, that convinced scientists that genes were composed of DNA instead of protein. By the time Hershey and Chase began those experiments, scientists had evidence that phages contained both DNA and protein. To distinguish between the DNA and protein in phages, Hershey and Chase used a technique called radioactive isotope labeling. During radioactive isotope labeling, researchers label phages with alternate forms of chemical elements, called isotopes, that emit unique radioactive signals. Hershey and Chase used a phosphorus label to identify DNA because DNA contains phosphorus but no sulfur, and a sulfur label to identify protein because the amino acids of proteins can contain sulfur but no phosphorus.

In the early 1950s at the Carnegie Institution, Hershey and Chase conducted experiments that demonstrated that the protein and DNA parts of phages separated when phages infected bacteria. Hershey and Chase demonstrated that when phages infected bacteria, the phages adhered to the outer membranes of the bacteria and injected their DNA into the host bacteria. The infection process resulted in empty phage protein shells that remained stuck to the outer bacterial membranes. In 1952, Hershey and Chase conducted the Waring blender experiment. They used a kitchen blender called the Waring Blender because the slow stir speed could remove phage protein coats stuck to the bacterial membranes without damaging the bacteria. That allowed Hershey and Chase to isolate the phage material that entered the cell. Hershey and Chase showed that phages injected only their DNA into bacteria during infection, and that DNA served as the genetic replicating element of phages whose replication eventually resulted in bacterial cells bursting.

According to historians, Hershey and Chase largely succeeded in convincing scientists that genes were made of DNA. Prior to the publication of his and Chase’s results, Hershey sent letters to his colleagues describing his experimental findings. In 1952, James Watson, a scientist who would later propose a structure for DNA, presented Hershey’s findings at a symposium in Oxford, United Kingdom. Many scientists, including Delbrück, praised Hershey for his and Chase’s experiments.

Throughout the rest of the 1950s and into the early 1960s, Hershey focused on developing experimental methods to study DNA. Chase left Hershey’s lab in 1953 and their collaboration ended. In 1955, Hershey addressed some issues with the Waring Blender experiment, acknowledging that small amount of protein was injected with DNA during phage infection and that he could not identify the function of that protein. However, according to Hershey, that finding did not dissuade scientists from supporting the view that genes were made of DNA. From 1953 to the early 1960s, Hershey worked to develop experimental methods to analyze chromosomes, or the extended, thread-like structure of DNA, in T2 and T4 phages. In 1958, Hershey was elected to the National Academy of Sciences headquartered in Washington DC.

Beginning in the early 1960s and continuing into the 1970s, Hershey studied the DNA chromosome structure for a type of phage called phage λ, or lambda phage. In the mid-1960s, Hershey found that the shape of DNA in phage λ was a single, circular molecule, rather than a linear strand-like in other phages and microorganisms. Later, Hershey wrote multiple essays on phage λ. In 1969, he, Delbrück, and Luria shared the Nobel Prize in Physiology or Medicine for their research about the replication mechanisms and the genetic structure of viruses. Hershey won the award specifically for his phage research and for the Hershey-Chase experiments. In 1971, he edited The Bacteriophage λ , a book detailing research about phage λ. Hershey continued to conduct research until his retirement in 1974.

Many scientists wrote memoirs about Hershey describing his character and effect on the scientific community. Watson detailed Hershey’s post-retirement interests in sailing, gardening, and computers. Franklin Stahl, a scientist who researched phages and DNA replication, wrote about Hershey’s originality, manner of scientific writing, and his thoroughness as an editor.

Hershey died from congestive heart failure on 22 May 1997 at his home in Syosset, New York.

• Altman, Lawrence K. "Alfred D. Hershey, Nobel Laureate for DNA Work, Dies at 88." New York Times , May 24, 1997. https://www.nytimes.com/1997/05/24/us/alfred-d-hershey-nobel-laureate-for-dna-work-dies-at-88.html (Accessed July 25, 2018).
• Avery, Oswald, Colin MacLeod, and Maclyn McCarty. "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III." The Journal of Experimental Medicine 79 (1944): 137–58. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2135445/pdf/137.pdf (Accessed July 18, 2018).
• Cairns, John. “Alfred Hershey (1908-97).” Nature 388 (1997): 130.
• Campbell, Allan, and Franklin W. Stahl. “Alfred D. Hershey.” Annual Review of Genetics 32 (1998): 1–6.
• Fischer, Ernst Peter, and Carol Lipson. Thinking About Science: Max Delbrück and the Origins of Molecular Biology. New York: W. W. Norton & Company, 1988.
• Fry, Michael. “Chapter 4 – Hershey and Chase Clinched the role of DNA as Genetic Material: Phage Studies Probelled the Birth of Molecular Biology.” In Landmark Experiments in Molecular Biology , 111–42. Academic Press, 2016.
• Hershey, Alfred Day, and Jacques Bronfenbrenner. “On Factors Limiting Bacterial Growth. I.” Proceedings of the Society for Experimental Biology and Medicine 36 (1937): 556–61.
• Hershey, Alfred Day, Kalmanson, George M., and Jacques Bronfenbrenner. “Quantitative Methods in the Study of the Phage-Antiphage Reaction.” Journal of Immunology 46 (1943): 267–79.
• Hershey, Alfred D., and Martha Chase. “Independent Functions of Viral Protein and Nucleic Acid in Growth of Bacteriophage” The Journal of General Physiology 36 (1952): 39–56.
• Huston, Ralph C., Huddleson, Irvin, F., and Alfred Day Hershey. “The Chemical Separation of Some Cellular Constituents of the Brucella Group of Micro-Organisms.” PhD diss., Michigan State College, 1934.
• Holmes, Frederic L. Meselson, Stahl, and the Replication of DNA: A History of “The Most Beautiful Experiment in Biology.” New Haven: Yale University Press, 2001.
• Hopson, Janet L., and Norman K. Wessells. Essentials of Biology. New York: McGraw-Hill, 1990.
• Judson, Horace Freeland. The Eighth Day of Creation. Cold Spring Harbor: Cold Spring Harbor Laboratory Press, 1996.
• Kalmanson, George, and Jacques Bronfenbrenner. “Studies on the Purification of Bacteriophage.” The Journal of General Physiology 23 (1939): 203–28. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2237916/pdf/203.pdf (Accessed July 25, 2018).
• Luria, Salvador, and Max Delbrück. “Mutations of Bacteria from Virus Sensitivity to Virus Resistance.” Genetics 28 (1943): 491–511. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1209226/pdf/491.pdf (Accessed July 25, 2018).
• Morange, Michel. A History of Molecular Biology. Cambridge: Harvard University Press, 1998.
• Olby, Robert Cecil. The Path to the Double Helix: The Discovery of DNA. Seattle: University of Washington Press, 1974.
• Shampo, Marc A., and Robert A. Kyle. "Alfred Hershey—Nobel Prize for Work in Virology." Mayo Clinic Proceedings 79 (2004): 590.
• Stahl, Franklin W., and Hershey, Alfred D. We Can Sleep Later: Alfred D. Hershey and the Origins of Molecular Biology. Woodbury: Cold Spring Harbor Laboratory Press, 2000.
• Watson, James, and Francis Crick. “Molecular Structure of Nucleic Acids.” Nature 171 (1953): 737–738. https://profiles.nlm.nih.gov/ps/access/SCBBYW.pdf (Accessed July 25, 2018).

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Gallery 18: Alfred Hershey and Martha Chase, 1953

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Alfred Hershey and Martha Chase at Cold Spring Harbor, 1953.

martha chase, cold spring harbor, alfred hershey

• Source: DNALC.DNAFTB

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