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Question: During DNA replication, the term leading strand is applied to the one which replicates in A. \(5'-...

During DNA replication, the term leading strand is applied to the one which replicates in
A. 5′−3′5'-3' direction continuously
B. 3′−5′3'-5' direction continuously
C. 5′−3′5'-3' direction discontinuously
D. 3′−5′3'-5' direction discontinuously

Explanation

Solution

Replication is a process that is carried out by a cell during the time of producing daughter cells. Each daughter cell contains the same DNA content as of its parents. The replication process is responsible for the duplication of the parent cell DNA. During the replication process, the DNA is formed by two strands. These are the leading and lagging strands. The leading strand forms first at the replication fork. It grows towards the replication fork as compared to the lagging strand.

Complete answer:
DNA replication is a process in which the DNA or deoxyribonucleic acid makes its copies that can be used in cell division. Two identical replicas of the DNA are formed from the one original DNA at the end of this process. Each newly formed strand consists of a strand from the original DNA. The original DNA uncoils and separates to form a replication fork. Each strand of replication fork serves as a template for the production of a new strand. The primer binds to the original DNA and then the DNA Polymerase moves in 5′−3′5'-3'direction adding up the bases to make new nucleotide sequences. The bases are added continually in the leading strand. But in the other strand that is the lagging strand, the bases are added in breaks.
Option A is that the leading strand replicates in 5′−3′5'-3' direction in a continuous manner.
Option B is that the leading strand replicates in 3′−5′3'-5' direction which is incorrect as it is the direction in which the lagging strand replicates. Also, the leading strand elongates continuously not discontinuously. It is characteristic of a lagging strand to replicate discontinuously in fragments.
Option C is that the leading strand replicates in 5′−3′5'-3' direction in a discontinuous manner. The direction is right but the manner is wrong. Thus, this is incorrect.
Option D is that the leading strand replicates in 3′−5′3'-5' direction in a continuous manner. Here, the direction is wrong but the manner is right. But, this is also an incorrect answer.
Therefore, the correct option is option A.

Note: The elongation of the leading strand happens at a faster rate than the lagging strand. Also, the fragments of the lagging strand that are called Okazaki fragments require DNA ligase to join them but in the leading strand, no DNA ligase is needed.