DNA as Genetic Material Hershey And Chase Experiment: Overview and Diagram

The Hershey and Chase experiment was a turning point in the field of genetics that confirmed that DNA is the genetic material. It was conducted in 1952 by Alfred Hershey and Martha Chase. The experiment involved the use of bacteriophages, which infect bacteria. They used radioactive labelling to track that DNA of the virus entered the bacteria. This experiment formed the molecular basis of inheritance, proving that DNA, and not protein, is the genetic material.

This Story also Contains

1. History Of Hershey And Chase Experiment
2. The Hershey And Chase Experiment
3. Results Of The Experiment
4. Conclusion Of The Experiment
5. Implications Of The Experiment
6. Recommended video for The Hershey And Chase Experiment
7. MCQs on Hershey and Chase Experiment

The results of their experiments played a vital role in understanding the flow of genetic material from DNA to RNA and then proteins, forming the foundation of the central dogma of molecular biology. It highlighted DNA’s role in regulating cellular processes and carrying genetic information. The findings of the experiment have been used in various fields like genetic engineering, medicine, and biotechnology.

History Of Hershey And Chase Experiment

The discovery of DNA as the genetic material was a major breakthrough in molecular biology. Until then, scientists were confused whether proteins or DNA carried genetic information. Alfred Hershey, an American bacteriologist and Nobel Prize winner, and Martha Chase, a research assistant who worked under him, together at Cold Harbor Laboratory performed the experiment. In 1952, they conducted the experiments using a virus called bacteriophage that infects bacteria. They used radioactive labelling to track DNA and proteins and observed that only DNA entered the bacterial cell. Their findings proved that DNA and not proteins, is the genetic material responsible for the process of heredity, thus laying the foundation of molecular biology.

The Hershey And Chase Experiment

The Hershey and Chase experiment was a major turning point in understanding the molecular basis of inheritance. Their findings proved that DNA carries genetic information. They used radioactive labeling to distinguish between DNA and protein to check which one enters bacterial cells during infection. This experiment solved one of the major mysteries of that time.

Objective

The main aim of the Hershey and Chase experiment was to find out if DNA or rather protein is the genetic material in viruses. They wanted to check which of the two enter the bacteria and would direct the production of new viral particles.

Materials And Methods

Bacteriophages (T2 phages): These are viruses that infect bacteria. Since these bacteriophages just possess a protein coat with DNA, it helped the experiment in determining which component carries the genetic information.

E. coli Bacteria: A common bacterium, used as host for the T2 phage in this experiment.

Isotopes Used

Phosphorus-32 (P-32): This isotope was used to label DNA because DNA contains phosphorus. The bacteriophages were allowed to infect the bacteria and the radioactive DNA is labelled with phosphorus 32.

Sulfur-35 (S-35): This isotope was used to label proteins, since proteins contain sulfur but DNA does not. The phages were used to infect the bacteria following the labelling of the radioactive protein coat of the phages.

Bacteriophages were cultured in a culture medium made with radioactive phosphorus (P-32). The obtained phages were marked with radioactive DNA.

Labelling Of Proteins With Sulfur-35:

Bacteriophages were grown in a culture medium containing radioactive phosphorus (P-32), so the DNA became radioactive. The remaining bacteriophages were grown in a culture medium with radioactive sulphur (S-35), resulting in radioactive proteins on the coat of the bacteriophage.

Infection Of E. Coli With Labeled Bacteriophages:

E. coli cultures were infected with either P-32 or S-35 labelled phages to label the components entering the bacterial cells.

Breakage And Centrifugation:

After the infection was completed, the mixture was agitated to separate phage coats from bacterial cells. It was then centrifuged to separate the heavier bacterial cells from the lighter phage coats.

Radioactivity Measurements:

Radioactivity was measured in the bacterial cells (pellet) and the viral protein coats (supernatant), to determine the location of the P-32 and S-35 isotopes.

Results Of The Experiment

The P-32 labelled DNA was found inside the E. coli cells, and the S-35 labelled protein remained out of the cells in the liquid. Therefore, it can be deduced that only the DNA entered the bacterial cells and was responsible for the production of new phages.

Conclusion Of The Experiment

It can be concluded from the Hershey and Chase experiment that DNA was the genetic material. It was the DNA, not that protein, of the bacteriophage that was injected into the bacteria and gave instructions to produce a new generation of viruses.

Implications Of The Experiment

The Hershey and Chase experiment was influential in molecular biology, providing concrete evidence that DNA is the genetic material. It later helped in the discovery of its structure and function. This experiment resulted in the determination of the DNA double helix structure by James Watson and Francis Crick in the year 1953. Their findings led to huge advancements in genetic engineering, genomics, and medical research.

The fact that DNA is the molecule of heredity was crucial in further studies of how the information encoded in genes is stored, replicated, and expressed. This discovery has also contributed towards progress in techniques such as the sequencing of DNA, polymerase chain reaction (PCR), and genetic cloning.

Recommended video for The Hershey And Chase Experiment

MCQs on Hershey and Chase Experiment

Q1. Unequivocal proof that DNA is the genetic material was first proposed by

1. Frederick Griffith

2. Alfred Hershey and Martha Chase

3. Avery, Macleod and McCarty

4. Wilkins and Franklin

Correct Answer: 2) Alfred Hershey and Martha Chase

Explanation:

Alfred Hershey and Martha Chase conducted the Hershey-Chase experiment in 1952, which provided unequivocal proof that DNA is the genetic material. In their experiment, they used bacteriophages, which are viruses that infect bacteria. They labelled the DNA of the bacteriophage with radioactive phosphorus-32 and the protein coat with radioactive sulfur-35.

By infecting bacteria with these labelled bacteriophages and then separating the viral DNA and proteins from the infected bacteria, Hershey and Chase showed that only the radioactive DNA, not the protein, was transferred to the next generation of phages. This demonstrated that DNA, not protein, carried the genetic information and served as the hereditary material.

Their experiment provided strong evidence supporting the idea that DNA, rather than protein, is the genetic material responsible for the transmission of inherited traits. Therefore, Hershey and Chase were the ones who first proposed the unequivocal proof that DNA is the genetic material.

Hence, the correct answer is Option 2) Alfred Hershey and Martha Chase.

Q2. If you want to obtain precise information regarding the exact time and location of synthesis of new DNA, which of the following methods would be most effective for such a study?

1. Electron microscopy

2. Carbon dating

3. Isolating and extracting DNA after regular intervals and estimating DNA amount

4. Using radioactive precursors of nucleic acids.

Correct Answer: 4) Using radioactive precursors of nucleic acids.

Explanation:

Using radioactive precursors of nucleic acids can indeed be an effective method for studying the synthesis of new DNA and obtaining precise information about the time and location of synthesis. Here's how it works:

Incorporation of Radioactive Precursors: Radioactive nucleotide precursors, such as radioactive isotopes of thymidine (e.g., tritiated thymidine or [3H]thymidine), can be added to the cell culture or organism under investigation. These radioactive precursors are incorporated into the newly synthesized DNA molecules during replication.

Detection of Radioactivity: Since the radioactive isotopes emit radiation, their presence in the newly synthesized DNA can be detected using various techniques. One commonly used method is autoradiography. The cells or tissues are exposed to a photographic film or an imaging plate, which records the emitted radiation as dark spots or lines on the film or plate. The intensity and location of the radioactive signals provide information about the rate and location of DNA synthesis.

Time Course Analysis: By exposing the cells or organisms to the radioactive precursors for different durations, it is possible to perform a time course analysis. This helps determine the exact time when DNA synthesis occurs. By analyzing samples taken at different time points, you can observe the progression of radioactivity incorporation and identify the stage of DNA synthesis.

Localization of DNA Synthesis: Depending on the specific research question, the study can be conducted at the cellular or tissue level. For cellular-level studies, cells can be labeled individually and examined under a microscope to identify which cells are actively synthesizing DNA. For tissue-level studies, sections of the tissue can be analyzed to determine the specific regions or cell types that are involved in DNA synthesis.

Hence, the correct answer is option 4) Using radioactive precursors of nucleic acids.

Q3. Alfred Hershey and Martha Chase worked on virus called:

1. Bacteriophage

2. -174

3. Reovirus

4. Retrovirus

Correct Answer: 1) Bacteriophage

Explanation:

Bacteriophages - The bacteriophages attach to the bacteria and its genetic material cells. The bacterial cell treats the viral genetic material as its own and manufactures more virus particles. Hershey and Chase worked to discover whether it was protein or DNA from a virus that entered the bacteria.

Hence, the correct answer is Option 1) Bacteriophage.

Also Read:

• MCQs on Hershey and Chase Experiment

• Properties of Genetic Material

• Genetic Code