Textbook Question
Explain how the Hershey and Chase experiment identified DNA as the hereditary molecule.
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7. DNA and Chromosome Structure
DNA as the Genetic Material
1:56 minutesProblem 6
Textbook Question
Why were ³²P and ³⁵S chosen for use in the Hershey–Chase experiment? Discuss the rationale and conclusions of this experiment.
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Identify the purpose of the Hershey–Chase experiment, which was to determine whether DNA or protein is the genetic material in phages.
Understand that ³²P (phosphorus-32) was used to label DNA because DNA contains phosphorus, but proteins do not.
Recognize that ³⁵S (sulfur-35) was used to label proteins because proteins contain sulfur (in amino acids like cysteine and methionine), but DNA does not.
Explain that after allowing the phages to infect bacteria, the researchers used a blender to separate the phage coats from the bacterial cells and then used a centrifuge to separate the components.
Conclude that the radioactive ³²P was found inside the bacterial cells, indicating that DNA is the genetic material, while the ³⁵S remained with the phage coats, showing that proteins were not the genetic material.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hershey-Chase Experiment
The Hershey-Chase experiment, conducted in 1952, was pivotal in demonstrating that DNA is the genetic material. By using bacteriophages (viruses that infect bacteria), the experiment showed that when these viruses infect bacteria, only the DNA enters the bacterial cells, not the protein coat. This provided strong evidence that DNA, not protein, carries genetic information.
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Radioactive Isotopes
In the Hershey-Chase experiment, radioactive isotopes ³²P (phosphorus) and ³⁵S (sulfur) were used to label DNA and proteins, respectively. Phosphorus is a key component of DNA, while sulfur is found in proteins but not in DNA. This distinction allowed researchers to track which molecule was transmitted into the bacterial cells during infection, leading to clear conclusions about the role of DNA.
Genetic Material
The concept of genetic material refers to the substance that carries and transmits genetic information in living organisms. Prior to the Hershey-Chase experiment, the identity of genetic material was debated, with proteins being a strong candidate. The experiment's findings established DNA as the primary genetic material, fundamentally changing our understanding of heredity and molecular biology.
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