1. In order to demonstrate that DNA (and not protein) was the genetic material,
ID: 49507 • Letter: 1
Question
1. In order to demonstrate that DNA (and not protein) was the genetic material, bacteriophage T4 were labeled with either 32P or 35S and allowed to infect E. coli.
a. What does 32 P label?
b. What does 35S label?
c. The bacteriophage that were produced from this infection retained which label 32P or 35S?
d. How did this experiment show that DNA was the genetic material?
2. Briefly, discuss the pros and cons of having a nucleoid (as bacteria do) versus a double nuclear membrane surrounding the DNA (as in eukaryotes).
3. Histones and other DNA binding proteins usually have a net positive charge. Explain
Explanation / Answer
By performing the Hershey-Chase series of experiments we can prove that the DNA (deoxyribonucleic acid) is responsible for bacterial transformation, but not the proteins. In this, the first step of experiments is, preparation of bacteriophage labelled with radioactive isotopes. They are then inserted into the bacteria, followed by bacterial incubation.
The incubated bacteria releases number of bacteriophages now and these progeny should be examined for the presence or absence of radioactive isotopes.
Bacteriophage is a viral vector that can infect bacteria; the virus contains DNA packed within protein core. If bacteria are infected with viral vector, part of the virus enters the bacterium, and after approximately 4hrs of incubation, the bacteria releases viruses in dozens.
In the parent bacteriophages, the phosphorus present on deoxyribose-phosphate (of DNA backbone) is labelled with phosphorous radio-isotope (32P), followed by their insertion into the bacteria and incubation. The same is repeated using sulphur isotope (35S), because only amino acids of proteins contain sulphur. The resultant progeny shows 1/3rd of the original phosphorus isotope and lack sulphur isotope, which indicates the DNA, is responsible for bacterial transformation.
.a. 32 P labels DNA
b. 35 S labels amino acid
c. The bacteriophage shows 32 P labelling because DNA is the genetic material.
d. As sufur is abscent in geneti material, its absence in the bacteriophage indicates protein is not the genetic materia, and as it is labellled with 32 P, it clearly shows DNA is the genetic material
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