Answer :
DNA replication always proceeds by adding new bases to the 3' end of an existing strand. Thus the correct answer is option (C).
Before DNA replication can start, the DNA molecule's double helix structure needs to be "unzipped." By rupturing the hydrogen bonds holding the complementary bases of DNA together, an enzyme known as helicase achieves this (A with T, C with G). The separation of the two single strands of DNA results in the formation of a replication "fork." The new DNA strands will be made using the two split strands as models. One of the strands that are oriented from 3' to 5' is the leading strand (towards the replication fork). The other strand is oriented in the 5' to 3' position and is referred to as the lagging strand (away from the replication fork). Due to their differing orientations, the two strands reproduce in two distinct ways. The end of the leading strand is then bound by a small piece of RNA called a primer, which is produced by the enzyme primase. The primer acts as the first template for creating DNA. DNA polymerase "walks" along the leading strand of DNA in the 5' to 3' orientation, adding new complementary nucleotide bases A, C, G, and T. It is regarded as replication that occurs continuously. The RNA primers that the primase enzyme generates bind in various places along the lagging strand. Then, Okazaki fragments—pieces of DNA also oriented 5' to 3'—are added to the lagging strand to complete the reaction.
This type of replication is called discontinuous replication because the Okazaki fragments will eventually need to be joined together. Exonuclease, a base-matching enzyme, eliminates the primer once all bases have matched (A with T, C with G) (s). The gaps created by the primer(s) are then filled in with additional complementary nucleotides.
The new strand is proofread to ensure that the new DNA sequence is error-free.
The DNA ligase enzyme then seals the DNA sequence into two continuous double strands. DNA replication results in the production of two DNA molecules, each of which is composed of an old and a new chain of nucleotides. DNA replication is said to as semi-conservative since only half of the replication chain is made up of the original DNA molecules. After replication, the newly produced DNA immediately creates a double helix.
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