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Diagram of Hershey Chase experiment. 1- One batch of phage was labeled with 32P which is incorporated into the DNA. Another batch is labeled with 35S which is incorporated into the protein coat. 2 – Bacteria were infected with the phage. The researchers were looking to identify if viral DNA or viral protein entered the host cell. 3 – Each culture is blended and centrifuged to separate the phage from the bacteria. The centrifuge separates the lighter phage particles from the heavier bacterial cells. 4 – Bacteria infected with phage 32P labeled DNA produce 32P labeled phage. Bacteria infected with 35S labeled phage produced unlabeled phage.
Martha Chase and Alfred Hershey conducted an experiment separately labeling the DNA and proteins of the T2 bacteriophage to determine which component was the genetic material responsible for the production of new phage particles.

By the time Hershey and Chase published their experiment in the early 1950s, microbiologists and other scientists had been researching heredity for over 80 years. Building on one another’s research during that time culminated in the general agreement that DNA was the genetic material responsible for heredity ( [link] ). This knowledge set the stage for the age of molecular biology to come and the significant advancements in biotechnology and systems biology that we are experiencing today.

  • How did Hershey and Chase use microbes to prove that DNA is genetic material?
A timeline. 1865: Mendel documents patters of heredity in pea plants. 1869L Miescher first identifies DNA (“nuclein”). 1902: Sutton and Boveri propose chromosome theory of heredity. 1915: Morgan and his “Fly Room” colleagues confirm the chromosome theory of heredity. 1927: Muller shows that X-rays induce mutation. 1928: Griffith’s “transformation experiments” transform non-pathogenic bacterial strains to pathogenic. 1930’s: Mammerling shows that hereditary information is contained in the nuclei of eukaryotic cells. 1930: McClintock demonstrates genetic recombination in corn. 1941: Beadle and Tatum describe the “one gen-one enzyme” hypothesis. 1944: Avery, McLeod, and McCarty show that DNA is the “transforming principle” responsible for heredity. 1950: Chargaff discovers that A=T and C=G (Chargaff’s rules). 1952: Hershey and Chase use radioactive labeling to prove that DNA is responsible for heredity. 1953: Watson and Crick propose the double helix structure of DNA. 1961: Jacob and Monod propose the existence of mRNA. 1990’s: Genome sequence projects begin.
A timeline of key events leading up to the identification of DNA as the molecule responsible for heredity

Key concepts and summary

  • DNA was discovered and characterized long before its role in heredity was understood. Microbiologists played significant roles in demonstrating that DNA is the hereditary information found within cells.
  • In the 1850s and 1860s, Gregor Mendel experimented with true-breeding garden peas to demonstrate the heritability of specific observable traits.
  • In 1869, Friedrich Miescher isolated and purified a compound rich in phosphorus from the nuclei of white blood cells; he named the compound nuclein. Miescher’s student Richard Altmann discovered its acidic nature, renaming it nucleic acid . Albrecht Kossell characterized the nucleotide bases found within nucleic acids.
  • Although Walter Sutton and Theodor Boveri proposed the Chromosomal Theory of Inheritance in 1902, it was not scientifically demonstrated until the 1915 publication of the work of Thomas Hunt Morgan and his colleagues.
  • Using Acetabularia, a large algal cell, as his model system, Joachim Hämmerling demonstrated in the 1930s and 1940s that the nucleus was the location of hereditary information in these cells.
  • In the 1940s, George Beadle and Edward Tatum used the mold Neurospora crassa to show that each protein’s production was under the control of a single gene, demonstrating the “one gene–one enzyme” hypothesis .
  • In 1928, Frederick Griffith showed that dead encapsulated bacteria could pass genetic information to live nonencapsulated bacteria and transform them into harmful strains. In 1944, Oswald Avery, Colin McLeod, and Maclyn McCarty identified the compound as DNA.
  • The nature of DNA as the molecule that stores genetic information was unequivocally demonstrated in the experiment of Alfred Hershey and Martha Chase published in 1952. Labeled DNA from bacterial viruses entered and infected bacterial cells, giving rise to more viral particles. The labeled protein coats did not participate in the transmission of genetic information.

Fill in the blank

The element ____________ is unique to nucleic acids compared with other macromolecules.

phosphorus

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In the late 1800s and early 1900s, the macromolecule thought to be responsible for heredity was ______________.

protein

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Short answer

Why do bacteria and viruses make good model systems for various genetic studies?

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Why was nucleic acid disregarded for so long as the molecule responsible for the transmission of hereditary information?

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Bacteriophages inject their genetic material into host cells, whereas animal viruses enter host cells completely. Why was it important to use a bacteriophage in the Hershey–Chase experiment rather than an animal virus?

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Questions & Answers

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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