Q.Describe how Hershey and Chase used radioactive sulphur (35S) and radioactive phosphorus (32P) to determine whether protein or DNA enters a bacterial cell during T2 bacteriophage infection.

Hershey and Chase showed that only viral DNA (not protein) enters the bacterium, so DNA is the genetic material.

Using bacteriophages labelled with radioactive phosphorus (32P in DNA) or radioactive sulphur (35S in protein), Hershey and Chase infected bacteria and then separated the phage coats by blending and centrifuging. Radioactive DNA (32P) was found inside the bacteria, while the 35S-labelled protein remained outside. They concluded that DNA is the genetic material that passes from virus into the host bacterial cell.

Alfred Hershey and Martha Chase (1952) used bacteriophage viruses (radioactively labelled) to prove that DNA, not protein, is the genetic material.

Hershey and Chase grew one batch of bacteriophage (T2 phage, which infects E. coli) with radioactive phosphorus (³²P, which labels DNA) and another batch with radioactive sulphur (³⁵S, which labels protein). They allowed the labelled phages to infect fresh bacteria, then agitated the culture in a blender to separate the phage coats (which remain outside the bacterium) from the bacterial cells (which contain the injected material), followed by centrifugation.

• Bacteria infected with ³²P-labelled phage became radioactive (DNA entered the cell).
• Bacteria infected with ³⁵S-labelled phage did NOT become radioactive (protein stayed outside).

Since only DNA entered the bacterial cell and directed the production of new phage progeny, this proved DNA (not protein) is the hereditary material. (Watson and Crick worked out DNA's structure, not this proof; Meselson-Stahl proved semiconservative replication; Avery-MacLeod-McCarty did the earlier transformation experiment in pneumococcus.)

By separately radiolabelling phage DNA and phage protein and tracking which one entered bacterial cells and produced new phage progeny, Hershey and Chase conclusively demonstrated that DNA (not protein) is the hereditary material.

Alfred Hershey and Martha Chase, in 1952, worked with the T2 bacteriophage, a virus that infects the bacterium Escherichia coli, consisting only of a protein coat surrounding a DNA core. They grew one batch of phages in a medium containing radioactive phosphorus (32P), which gets incorporated into DNA (since DNA, but not protein, contains phosphorus), and another batch in a medium with radioactive sulphur (35S), which gets incorporated into protein (since protein, but not DNA, contains sulphur amino acids). After allowing each labelled phage batch to infect separate E. coli cultures, they used a blender to shear off the empty phage coats from the bacterial cell surfaces and centrifuged the mixture to separate the coats (in the supernatant) from the infected bacterial cells (in the pellet). They found that the 32P (DNA) label was mostly found inside the bacterial cells, while the 35S (protein) label remained outside in the phage coats -- and the infected bacteria went on to produce new, fully-formed phage progeny. This showed that only the phage DNA entered the bacterial cell and carried the genetic instructions needed to direct the production of new phage particles, proving DNA is the genetic material, not protein.

In the Hershey-Chase experiment, after centrifugation, the cells contained radioactive phosphorus (³²P) but no radioactive sulfur (³⁵S), while the supernatant contained radioactive sulfur (³⁵S) but no radioactive phosphorus (³²P), proving DNA is the genetic material.

Hershey and Chase showed that the genetic material of the bacteriophage (virus) is DNA, not protein.

Alfred Hershey and Martha Chase (1952) worked with the T2 bacteriophage, which has only DNA and a protein coat:

• They labelled the DNA with radioactive phosphorus (32P) in one batch and the protein coat with radioactive sulphur (35S) in another.

• After the phages infected E. coli, only the 32P (DNA) label entered the bacteria; the 35S (protein) stayed outside in the empty coats.

• Since only DNA passed into the host and directed the production of new phages, they concluded that DNA is the genetic material of the virus.

The Hershey-Chase experiment used radioactively labelled bacteriophage DNA and protein to show that only DNA enters the bacterium and directs progeny virus formation.

Hershey and Chase grew one batch of bacteriophages with radioactive phosphorus (³²P, labelling DNA) and another batch with radioactive sulphur (³⁵S, labelling protein). Each batch was allowed to infect E. coli, then agitated in a blender to separate the phage coats (which remained outside the bacterial cell) from the bacterial cells. Only the ³²P (DNA) label was found inside the bacteria and in the progeny phages, while the ³⁵S (protein) label stayed in the supernatant with the empty phage coats. This proved that DNA, not protein, is the genetic material that enters the cell and is transmitted to progeny. (Schleiden & Schwann proposed the cell theory; Meselson & Stahl proved semiconservative DNA replication; Jacob & Monod proposed the lac operon model.)

Bacteriophages are bacteria-infecting viruses, famous for proving that DNA (not protein) is the genetic material.

A bacteriophage ('bacteria eater') is a virus that specifically infects bacteria. Structurally it has a protein coat (capsid) enclosing its genetic material, which may be DNA or RNA. On infection, the phage attaches to the bacterial cell surface and injects its genetic material into the host, while the protein coat stays outside; the injected nucleic acid then hijacks the bacterial machinery to make new phage particles. This behaviour was exploited by Hershey and Chase (1952) in their T2 bacteriophage experiment, which used radioactively labelled DNA (³²P) and protein (³⁵S) to conclusively show that DNA, not protein, is the hereditary material.

A virus that specifically infects bacterial cells is called a bacteriophage.

Viruses are obligate intracellular parasites that infect a wide range of hosts — plants, animals and bacteria. A virus that infects and replicates within bacteria is called a bacteriophage (literally, 'bacteria eater'). The most extensively studied bacteriophages are those that infect the bacterium Escherichia coli, such as the T-even phages (T2, T4). Bacteriophages played a historic role in molecular biology — the Hershey–Chase blender experiment (1952) used a bacteriophage (T2) infecting E. coli to prove that DNA, not protein, is the genetic material, since only the phage's DNA (labelled with radioactive ³²P) entered the bacterium while its protein coat (labelled with ³⁵S) remained outside.