Question

3. Describe the means by which Hershey and Chase established that only the DNA of a phage enters an E coli cell. What conclusions did these scientists draw based on these observations? 4. List the three components of a nucleotide.

Answer 1

3. Alfred Hershey and Martha Chase conducted an experiment in 1952 by infecting the Escherichia coli cells with bacteriophage. He labeled the phages with two different radioactive elements. One group of phages were labeled with a radioactive isotope of Phosphorus on their DNA(Deoxyribonucleic acid)and the other group was labeled with a radioactive isotope of Sulfur on their protein(phage coat). The bacteria were then infected with the two groups of bacteriophages. After centrifugation, it was observed that while the bacteria infected with the phosphorus labeled phages contained radioactivity in their cells, the bacteria infected with sulfur labeled phages showed no such radioactivity. Hence, it was concluded by the scientists that DNA is the genetic material and not protein.

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4. A nucleotide is the building block of the genetic material DNA(Deoxyribonucleic Acid) and RNA(Ribonucleic Acid).

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The bases can be either purine (Adenine and Guanine having two nitrogen-containing rings) or pyrimidines(Thymine, Cytosine or Uracil having one nitrogen-containing ring). The sugar can be Ribose(in RNA) or Deoxyribose(in DNA).