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Viral Reproduction and Genetics
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Viruses that attack bacteria are known as bacteriophages or phages. They consist of DNA surrounded by a protein coat. A long thread of DNA of about 150 genes is packed into a head from which a short tail projects. The phage attaches itself to the bacterial surface by its tail. The DNA thread is injected into the bacterium where it proceeds to replicate freely. New virus heads and tails are manufactured and then assembled within the cell under the influence of viral DNA. After some time the bacterium may burst open releasing the viruses, which then repeat the process in other bacterium. In 1952, the American scientists Alfred Hershey and Martha Chase demonstrated the only the viral DNA is responsible for directing operations in the bacterial cell. They used two samples of bacteriophage. In one they labelled the viral DNA with radioactive 32P. In the other they labelled the protein of the head and tail with 35S. DNA contains phosphorus and not sulphur, whereas protein contains sulphur and not phosphorus.
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