Question

In DNA replication, the leading strand is the one which replicates in
A. $5' \to 3'$ direction continuously
B. $3' \to 5'$ direction continuously
C. $5' \to 3'$ direction discontinuously
D. $3' \to 5'$ direction discontinuously

Answer 1

Hint: Replication is the transmission of chromosomal DNA from a generation to another generation and is achieved by providing two copies of the entire genome while being replicated. The model of DNA in which the parental DNA gives rise to two identical daughter duplexes, each containing one original and one parent strand is called replication is known as semiconservative replication. The other two methods being conservative and dispersive.

Complete answer:
The replication occurs in three steps in both prokaryotes and eukaryotes. These are include-
• Initiation
• Elongation
• Termination

The elongation steps involve the synthesis of leading and lagging strands.
The helicase and Dna B unzips the double-stranded DNA for replication, making a forked structure. The primase then performs the task of generating short strands of RNA that bind to the single-stranded DNA to initiate DNA synthesis with the help of DNA polymerase. This enzyme can work only in the $5'$ to $3'$ direction, the replication of the leading strand is done continuously whereas lagging-strand replication is discontinuous, with short Okazaki fragments being formed and later linked together.
So, the leading strand is the one that replicates in the $5' \to 3'$ direction continuously.

Hence, the correct answer is option (A).

Note: DNA synthesis always takes place in the $5' \to 3'$ because of the elongation of chain results from the formation of a phosphodiester bond between the $3'$ OH of a growing strand and $\alpha - $ phosphate of a dNTP. The mode of replication in which one strand is synthesized continuously and the other discontinuously is known as semi-conservative replication.