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Question

The cells in a culture plate were treated with a compound X. However, it was observed that the DNA replication was not occurring properly. On exploring the underlying defects by experiments, it was observed that the replication fork was not formed. Predict the enzyme that has been degraded by compound X.

A
Ligase
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B
Helicase
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C
Topoisomerase
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D
DNA polymerase
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Solution

The correct option is B Helicase
DNA replication is accomplished by a wide array of enzymes. Helicase is the enzyme that acts first at the origin of replication and breaks the hydrogen bonds between double helix. This leads to strand separation at the origin of replication and a replication fork is formed.
After the action of primase, which initiates the RNA primer. DNA polymerase acts on to add dNTPs subsequently to the free 3’ OH group of the growing chain during replication.
The torsional strain generated in the process of unwinding and rewinding is relieved by the action of topoisomerase.
Ligase is involved in joining the fragments of DNA formed during replication.
Since, it is given that the replication fork was not formed, the compound X must have affected helicase, rendering it non-functional. Hence, the parental strands were not separated at the origin of replication and the replication fork was not formed.

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