Hershey and Chase

Hershey and Chase is the 1952 experiment showing that DNA, not protein, is the genetic material in bacteriophages. In Microbiology, it’s the classic proof that viral genetic instructions enter bacteria during infection.

What is Hershey and Chase?

Hershey and Chase is the classic Microbiology experiment that showed DNA, not protein, carries genetic information in a bacteriophage. They studied viruses that infect bacteria, especially phages that attack E. coli, and tracked which part of the virus actually entered the bacterial cell during infection.

Their idea was simple but clever. If the protein coat of the phage stayed outside the cell, then protein probably was not the hereditary material. If the viral DNA entered the cell and directed the making of new viruses, then DNA had to be the material carrying the instructions. They used radioactive sulfur, 35S, to label protein because proteins contain sulfur in some amino acids but DNA does not. They used radioactive phosphorus, 32P, to label DNA because DNA contains a phosphorus-rich backbone and proteins generally do not.

After letting the labeled phages infect E. coli, they used a blender to shear the empty protein coats off the bacterial surface. Then they separated the heavier bacteria from the surrounding fluid. The striking result was that the 32P labeled DNA was found inside the bacterial cells, while the 35S labeled protein stayed mostly outside in the fluid with the phage shells.

That result mattered because it answered a long-running question in genetics and virology. Scientists already suspected that something in chromosomes carried heredity, but DNA had been treated by many researchers as too simple to store instructions. Hershey and Chase helped settle that debate by showing, in a microbial system, that the information for making new viruses is inside the DNA.

In a Microbiology class, this experiment usually shows up as a model for how scientists use controls and tracers to follow a biological process. The phage is the delivery system, the label marks a molecule, and the blender step separates what entered the cell from what stayed outside. That sequence is the whole logic of the experiment: label, infect, separate, and compare where the radioactivity ends up.

Why Hershey and Chase matters in MICROBIO

Hershey and Chase matters in Microbiology because it connects viruses, bacterial infection, and genetics in one clean experiment. When you study bacteriophages, this is one of the first places where you see that a virus is more than a particle floating around outside a cell. It is a package of instructions, and those instructions have to get into the host cell to take over replication.

The experiment also sets up later ideas about the central dogma, DNA replication, and how genes are expressed. Once you accept that DNA carries the information, the next question becomes how that information is copied and used to build proteins. That makes Hershey and Chase a bridge between viral infection and molecular genetics.

It also gives you a pattern for interpreting lab evidence. You are not just memorizing that “DNA is genetic material.” You are learning how scientists proved it by separating variables, labeling different molecules, and checking which label moved into the bacteria. In microbiology labs and exam questions, that kind of reasoning shows up all the time, especially when you compare what is inside a virus, what enters a host cell, and what happens after infection.

The experiment is also a useful contrast with Griffith’s transformation experiments. Griffith showed that something from dead bacteria could transform living bacteria, but he did not identify the molecule. Hershey and Chase helped narrow the answer down to DNA. Together, the two experiments map the path from a mysterious hereditary factor to the molecular basis of infection and inheritance.

How Hershey and Chase connects across the course

Bacteriophage

Hershey and Chase used bacteriophages as their model system because phages make the entry step easy to track. A phage has a protein coat and a DNA core, so you can label each part separately and see which one gets into E. coli. That makes the virus a perfect tool for studying how genetic material moves during infection.

Radiolabeling

Radiolabeling is the method that made the experiment work. 35S marked the protein coat, and 32P marked the DNA, so the scientists could follow each molecule after infection. In microbiology labs and problem sets, this is a good example of using a tracer to answer a question about movement and location.

Genetic Material

This experiment is one of the strongest early proofs that DNA is genetic material. The key logic is not just that DNA was present, but that the DNA label entered the bacterial cell and carried the instructions for new phage production. That separates DNA from proteins as the molecule of inheritance.

Griffith's transformation experiments

Griffith’s work came first and showed that bacteria could be transformed by a heritable factor, but he did not identify the molecule. Hershey and Chase built on that kind of thinking by using a virus model and radioactive labels to show that the heritable material was DNA. Together, the two experiments form a sequence in genetic discovery.

Is Hershey and Chase on the MICROBIO exam?

A quiz item or lab question may show a diagram of labeled phages infecting bacteria and ask which isotope ended up inside the cells. You should connect 32P with DNA and 35S with protein, then explain that the DNA entered E. coli while the protein coat stayed outside. If you get a short-response prompt, trace the method in order: label the phage, infect the bacteria, separate with a blender, and check where the radioactivity is found.

You may also be asked to compare this experiment with Griffith’s transformation work or to explain why it changed the way scientists thought about heredity. The strongest answer is specific: the experiment used a bacteriophage model to show that DNA, not protein, carries the instructions for making new viruses.

Hershey and Chase vs Griffith’s transformation experiments

Both experiments are early proofs about heredity, and both involve bacteria, so they are easy to mix up. Griffith showed that a transforming principle existed, while Hershey and Chase identified DNA as that genetic material using labeled bacteriophages. Griffith pointed to a mystery factor, and Hershey and Chase traced the molecule directly.

Key things to remember about Hershey and Chase

• Hershey and Chase showed that DNA, not protein, enters bacterial cells and acts as the genetic material in bacteriophages.

• 35S labeled the protein coat, while 32P labeled the DNA, so the two parts of the virus could be tracked separately.

• The blender step stripped off the phage coats and let scientists separate what stayed outside from what got into E. coli.

• This experiment is a classic piece of microbiology because it links viral infection to genetic information.

• If you remember one thing, remember this: the DNA went into the bacteria and the protein did not.

Frequently asked questions about Hershey and Chase

What is Hershey and Chase in Microbiology?

Hershey and Chase is the 1952 experiment that proved DNA is the genetic material in bacteriophages. They used radioactive labels to show that DNA entered the bacterial cell during infection, while the protein coat stayed outside. In Microbiology, it is a major example of how scientists identified the molecule that carries hereditary information.

How did Hershey and Chase use radioactive labels?

They used 35S to label the phage protein coat and 32P to label the phage DNA. Since sulfur is found in proteins but not DNA, and phosphorus is found in DNA but not most proteins, each isotope marked a different molecule. After infection and blending, the labeled DNA was inside the bacteria, which showed where the genetic material was.

How is Hershey and Chase different from Griffith?

Griffith showed that some heritable substance from dead bacteria could transform living bacteria, but he did not identify it. Hershey and Chase went further by using bacteriophages and radioactive tracers to show that the heritable substance was DNA. So Griffith found the clue, and Hershey and Chase identified the molecule.

Why did they use bacteriophages instead of bacteria alone?

Bacteriophages gave them a clean way to separate protein from DNA and watch what entered the host cell. A phage has a protein shell and a DNA core, which makes it easier to label each part and follow infection. That design made the experiment much more direct than trying to sort out many molecules in a whole bacterial cell.