DNA as Genetic Material – Hershey And Chase Experiment

The Hershey and Chase Experiment, conducted in 1952 by Alfred Hershey and Martha Chase, demonstrated that DNA contains genetic information. They accomplished this by investigating viruses that infect bacteria, known as bacteriophages. In these tests, scientists labelled the virus’s DNA with a radioactive marker while labelling the protein coat independently with another marker.

When the viruses infected bacteria, researchers discovered that only the DNA identifier, not the protein marker, was passed along to the next generation of viruses. This helped to demonstrate that DNA, not protein, is the molecule that conveys genetic instructions. We will read about the Hershey and Chase Experiment in detail in this article.

Hershey and Chase Experiment

In 1952, Alfred Hershey and Martha Chase investigated bacteriophage, a virus that destroys bacteria. Their research focused on T2 bacteriophage that infects the bacterium Escherichia coli (E. coli). Their goal was to determine whether the T2 phage’s genetic instructions or information required for life, were stored in its DNA or protein coat. They wanted to show that the DNA, not the protein, contained this important genetic information.

There were three steps in the experiment:

1. Infection
2. Blending
3. Centrifugation

Alfred Hershey and Martha Chase used two forms of radioactive material, phosphorus-32 (32P) and sulfur-35 (35S), to designate the bacteriophages differently. Phosphorus is a component of DNA, the genetic material, whereas sulphur is present in proteins but not DNA.

They inserted these radioactive isotopes into the bacteriophages DNA (genetic material) and protein coat (capsid) separately. This enabled them to determine which parts of the virus entered the bacterial cell during infection. They then allowed the labelled viruses to infect E. coli bacterial cells.

Hershey and Chase Experiment Diagram

Following a brief time of infection, they mixed the liquid to separate the viral protein coatings from the bacteria. This blending phase ensured that any viral proteins that were not bound to bacterial cells were eliminated. They next centrifuged the mixture, causing the heavier bacterial cells to sink at the bottom of the tube while the lighter viral protein coatings (if present) remained in the liquid above, known as the supernatant.

The results demonstrated that bacterial cells infected with phages labelled with phosphorus-32 (32P) exhibited radioactivity. This suggested that the phages’ DNA entered the cells during infection. In contrast, bacterial cells infected with phages labelled with sulfur-35 (35S) exhibited little to no radioactivity, indicating that the phages’ protein coat (also known as capsid) did not enter the cells.

Based on these findings, Hershey and Chase concluded that DNA, rather than protein, serves as the genetic material transmitting bacteriophages’ hereditary information. This experiment offered solid proof that DNA is the chemical responsible for conveying genetic information in living beings.

DNA as Genetic Material

Scientists discovered that DNA is the primary factor in defining the characteristics of most living organisms. However, some viruses use RNA instead. So, for something to be genetic material, it must:

1. Be able to create clones of itself (self replicable).
2. Be stable structurally and chemicaly.
3. Allow for mutations, which can lead to evolution.
4. Be able to pass on traits according to Mendel’s inheritance principles.

Most other compounds, such as proteins, carbohydrates, and lipids, did not meet the previously listed criteria. While RNA could meet those requirements, DNA was favoured over RNA for genetic material for a number of reasons:

1. DNA has more structural stability than RNA.
2. DNA has higher chemical stability than RNA.
3. DNA has a double-stranded structure that allows it to effectively repair replication faults.
4. RNA is required for protein production because DNA cannot directly code for them.

Approximate content of DNA in few organisms is given below:

Species	DNA amount pg/per cell	No. of nucleotide pairs (in millions)
Bacteriophage T4	0.0024	0.7
Bacteria	0.002-0.06	2
Fungi	0.02-0.17	20
Sponges	0.1	100
Molluscs	1.2	1000
Crustaceans	3	2800
Fishes	2	2000
Amphibians	7	6500
Birds	2	2000
Reptiles	5	4500
Mammals	6	5500

What is the Pulse and Chase Experiment?

Pulse-Chase Analysis is similar to a time-lapse camera for investigating what happens inside cells. In this procedure, cells are first exposed to a labelled chemical (the “pulse”) that identifies certain molecules. Then they are given an unlabeled chemical (the “chase”) to observe what occurs. This allows scientists to track how molecules migrate and change over time.

Researchers have utilised this method to analyse a variety of proteins, including protein kinase C and ubiquitin, as well as to better understand processes such as Okazaki fragment production during DNA replication. For example, George Palade used pulse-chase with radioactive amino acids to study how cells release chemicals.

Conclusion -DNA as Genetic Material: Hershey And Chase Experiment

Alfred Hershey and Martha Chase conducted to confirm DNA as the genetic substance. The Hershey-Chase investigations was crucial then as at that time many scientists believed that proteins contained genetic information rather than DNA. Hershey and Chase discovered that when viruses called bacteriophages infect bacteria, a small amount of their protein enters the bacterial cell. This suggested that DNA, not protein, was responsible for carrying genetic instructions. These findings, coupled with previous and subsequent discoveries, strongly showed that DNA was the genetic material. Later they received the Nobel Prize in Physiology or Medicine for their contributions to genetics.

FAQs on DNA as Genetic Material – Hershey And Chase Experiment

What are the 3 Steps of Hershey and Chase Experiment?

Hershey and Chase carried their experiment in three steps : infection, blending, centrifugation.

What was the Hershey and Chase Experiment Class 12?

The Hershey and Chase experiment, conducted in 1952 by Martha Chase and Alfred Hershey, demonstrated that DNA, rather than protein, is the genetic material of viruses. They used bacteriophages to track the transmission of genetic information.

How did the Hershey and Chase Experiment Work?

In the experiment, bacteriophages were labeled with radioactive isotopes: sulfur-35 for proteins and phosphorus-32 for DNA. The phages were allowed to infect bacterial cells. After infection, the phage protein coats were removed by agitating the mixture in a blender, separating them from the bacterial cells.

What is the Principle of Hershey and Chase Experiment?

Hershey and Chase experiment proving DNA as the genetic material was based on the principle Transduction which is the process by which DNA is transferred from one bacterium to another by a virus.

Why was the Hershey and Chase Experiment Significant?

The Hershey and Chase experiment provided crucial evidence supporting the idea that DNA carries genetic information. This discovery was instrumental in shaping our understanding of genetics and laid the foundation for subsequent research in molecular biology, including the elucidation of the structure of DNA by Watson and Crick.

Is DNA the only Genetic Material?

There are three types of genetic materials: DNA, RNA, and genes.

Why was E.coli used in Hershey and Chase Experiment?

E. coli was used in the Hershey and Chase Experiment because it is easily grown and reproduces quickly, making it ideal for genetic research.

What Virus did Chase and Hershey Study?

Chase and Hershey studied the T2 bacteriophage virus in their experiment.

What was the Radioactive in the Hershey and Chase Experiment?

They used radioactive sulfur (S35) to label protein and radioactive phosphorus (P32) to label DNA.

What was the Conclusion of Hershey and Chase Experiment?

The conclusion of Hershey and Chase experiment was that DNA and not protein is the genetic material passed from viruses to bacteria.

How did Hershey and Chase Modify the Virus?

Hershey and Chase modified the virus by labeling its DNA with radioactive phosphorus to track its transmission into bacterial cells.