DNA replication
Read the following passage carefully and answer the given questions.
In addition to DNA-dependent DNA polymerases, many additional enzymes are required to complete the process of replication with high degree of accuracy. Since the two strands of DNA cannot be separated in its entire length (due to very high energy requirement), the replication occur within a small opening of the DNA helix, referred to as replication fork. The DNA-dependent DNA polymerases catalyse polymerisation only in one direction, that is 5′ → 3′. This creates some additional complications at the replicating fork. Consequently, on one strand (the template with polarity 3′ → 5′), the replication is continuous, while on the other (the template with polarity 5′ → 3′), it is discontinuous. The discontinuously synthesised fragments are later joined by the enzyme DNA ligase. After the completion of replication, each DNA molecule would have one parental and one newly synthesised strand. This scheme was termed as semiconservative DNA replication. In eukaryotes replication of DNA takes place at S-Phase of cell cycle.
Replication of DNA takes place at -
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → S Phase
The passage says that in eukaryotes DNA replication takes place in the S phase (synthesis phase) of the cell cycle. The S phase is a part of interphase. The amount of DNA per cell doubles in it, so that each daughter cell can later get a full copy.
(1) M Phase — Incorrect. The M phase is the phase of cell division (mitosis). The DNA has already been copied before it.
(2) G1 Phase — Incorrect. In G1 the cell grows before the DNA is copied.
(3) G2 Phase — Incorrect. G2 comes after the S phase. The cell prepares for division.
(4) S Phase — Correct. DNA is replicated in this phase.
Note 1: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
Note 2: A similar question was also asked in CUET (UG) 2025 on 15-05-2025 (Slot 1).