Q.100 Among the following statements, which is/are TRUE regarding the replication of
DNA?
(A) Replication is bidirectional and conservative in nature.
(B) Replication in eukaryotes takes place at multiple Ori sites simultaneously.
(C) Both the strands replicate in discontinuous manner.
(D) One strand replicates in continuous while the other replicates in discontinuous
manner.

Correct Answer: (B) and (D)

DNA replication involves precise mechanisms ensuring accurate genome duplication, with specific characteristics distinguishing prokaryotic and eukaryotic processes. Options B and D accurately describe key features verified through experimental evidence.

Option Analysis

Option (A): False
Replication proceeds bidirectionally from origins, forming two replication forks that move in opposite directions. However, it follows a semi-conservative mechanism, where each daughter DNA contains one parental and one new strand, not conservative (which keeps parental strands intact).​

Option (B): True
Eukaryotes possess large linear chromosomes requiring multiple origins of replication (Ori sites) distributed along each chromosome. These initiate simultaneously during S phase, enabling efficient genome duplication within the cell cycle timeframe.​

Option (C): False
Both strands do not replicate discontinuously; DNA polymerase synthesizes only in the 5’→3′ direction. This polarity creates distinct synthesis modes at the replication fork.​

Option (D): True
The leading strand synthesizes continuously toward the replication fork, while the lagging strand forms discontinuously via Okazaki fragments away from the fork. DNA ligase joins these fragments, termed semi-discontinuous replication.​

DNA replication ensures genetic continuity through bidirectional replication from origins, multiple Ori sites in eukaryotes, and semi-discontinuous synthesis where one strand replicates continuously and the other discontinuously. This process, vital for CSIR NET Life Sciences, follows semi-conservative rules proven by Meselson-Stahl experiments.​

Key Mechanisms

• Bidirectional Forks: Replication bubbles expand in both directions from each origin.​

• Eukaryotic Origins: Thousands of Ori sites fire simultaneously for timely S-phase completion.​

• Strand Synthesis:

  Strand Type	Direction	Mechanism	Enzyme Role
  Leading	Continuous, 5’→3′ toward fork	Single elongation	DNA Pol δ/ε ​
  Lagging	Discontinuous, Okazaki fragments	Multiple primers joined by ligase	DNA Pol α/δ ​

These features optimize efficiency despite antiparallel DNA strands and polymerase polarity constraints. For competitive exams, recognize semi-conservative over conservative models and eukaryotic multi-origin strategy versus prokaryotic single origin.​