2. What happened to the DNA after the phage was plasmolyzed? Why did this not ha

Question

2. What happened to the DNA after the phage was plasmolyzed? Why did this not happen to the protein?

3. Explain the antibody data in terms of what remains of phage particles when they become ghosts.

2. What happened to the DNA after the phage was plasmolyzed? Why did this not happen to the protein?

3. Explain the antibody data in terms of what remains of phage particles when they become ghosts.

4. The fragile attachment of phage to the outside of host bacteria led the scientists to allow attachment and then agitate the bacteria-phage to try to remove the latter. Then, the distributions of radioactive labels were determined. Also, the host bacteria were tested for their ability to be infected with phage, to determine whether the treatments with the blender harmed the bacteria. Data are shown in the figure. How do the distributions of the labeled protein and labeled DNA differ? What conclusion can you draw about the infection process?

Explanation / Answer

Hershy and Chase experiment conducted in 1952 proved that DNA, in fact, is the inherited material. The 35S was used to label phage proteins mainly Methionine and cysteine AAs and 32P was used to label the DNA backbone.

The four conditions in the table were further used to analyse the result.

a.percent isoptope which is acid soluble

b.percent isotope which is acid soluble after DNAse treatment (after DNAse treatment, DNA would be fragmented into smaller oligonucleotides, therefore, aiding in its solubility).

c.percentage isotopes adsorbed onto sensitive bacteria (Phage adsorbtion onto bacterial surface happens due to a type of ligand-receptor interaction, that of tail fibres attaching onto receptors on bacterial surface.

d percent isotope precipitated by antiphage ( antiphage particles are antibodies against proteins that form phage coat)

Plasmolysis result in separation of phage into two parts such that the DNA is released in water as free acid and the sulphur rich coat stays intact.

1. When intact phage particles are treated with DNAse, the enzyme is unable to fragment DNA as it remains protected by the protein-rich capsid. however, in the case of plasmolyzed phage particles, The DNA now in the solution is easily acted upon by the DNA fragmenting enzyme. This explains why there is only 1% 32P detected in case of intact phage but 80% 32P detected in case of plasmolysed phage.

2.The DNA in intact phage remains unharmed while in case of plasmolyzed phage it gets fragmented. There is no effect on 35S labelled protein as DNAse selectively cleaves DNA.

3. Both intact phage and ghosts have an outer capsid which is rich in protein. the antiphage particles react with capsid proteins and precipitate. Therefore more than 90% isotope is detected in case of precipitation with antiphage. The plasmolysed phage retaining capsid is called the ghost. Since there is no capsid in case of plasmolysed 32P labelled phage, there is only 5% isotope detection in this scenario.

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