Q. 18

Hershey and Chase

Answer :


1. In the year 1952, Alfred Hershey and Martha Chase did an experiment to detect the presence of genetic material. For this experiment they took a virus called ‘Bacteriophage’.


2. The virus was grown in two separate mediums. One medium consisted radioactive phosphorus (P32). The other medium consisted of radioactive Sulphur (S35).


3. Medium containing radioactive Phosphorous had radioactive DNA because DNA is a phosphorus-basedstructure. Medium containing radioactive sulphur had radioactive protein.


INFECTION:


Now, these viruses were injected into a bacterium called E. coli.


CENTRIFUGATION AND BLENDING:


1. For this incorporation of Virus into E. coli, viral coats were removed by agitating them in the blender.


2. E. coli infected with virus had radioactive DNA and no radioactive proteins were present.


3. This showed that ‘DNA’ was the genetic material that got transferred from virus to E. coli and not protein.


OR


a)DNA replication occur within a replication fork and not in its entire length simultaneously because DNA cannot be separated completely as it requires very high energy and polymerization takes place only in one direction which is 5’-3’, hence replication occurs only in small fragment of the DNA called as replication fork.


b) DNA replication occur within a replication fork and not in its entire length simultaneously because DNA cannot be separated completely as it requires very high energy and polymerization takes place only in one direction which is 5’-3’, hence replication occurs only in small fragment of the DNA called as replication fork.On one strand which is 3’-5’ the replication is continuous and the other strand which has polarity 5’-3’ the replication is discountinous , these fragments known as okazaki fragments are later joined together by DNA Ligase enzyme.


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