[问答题]
The Hershey-Chase experiment
-vn ,a2r a;-shnwka z5in 1952 in
a+ bq30 rmihc5volved cultured viruses that were radioactively la
3cmbq h r+0ia5belled with either sulfur ($^{35}$S) or phosphorus ($^{32}P) in two separate flasks. Each batch of viruses was then added to separate cultures of bacteria. After allowing time for the viruses to infect the bacteria, the culture solutions were centrifuged to separate the viral remains from the bacterial cells, forming two layers, the pellet and the supernatant.
1.State reasons for using radioactive sulfur ($^{35}$S) and phosphorus ($^{32}$P).
2.Suggest one technological development, other than radioisotopes, that helped open up possibilities in understanding the overall structure of DNA.
3.1.Outline the results of the experiment that provided evidence to support the conclusion that DNA is the genetic material.
3.2.Describe how the 4 nitrogenous bases of DNA enables polypeptides to be coded for.
4.Explain how DNA can be packaged into compact units to form chromatin.
