In which phase of the cell cycle does Deoxyribonucleic acid (DNA) replication occur?

From the Guidelines

The correct answer is (c) S phase, as DNA replication occurs specifically in this phase of the cell cycle, according to the most recent and highest quality study 1. During the cell cycle, the process of DNA replication is crucial for the duplication of genetic material. The cell cycle consists of interphase (G1, S, and G2 phases) followed by mitosis (M phase).

• In G1 phase, the cell grows and prepares for DNA synthesis.
• Then in S phase, the cell duplicates its entire DNA content, creating two identical copies of each chromosome, as performed by polymerase enzymes 1.
• After DNA replication is complete, the cell enters G2 phase where it continues to grow and prepares for cell division.
• Finally, in M phase, the replicated chromosomes separate, and the cell divides into two daughter cells. The S phase is characterized by the synthesis of new DNA, and this process is tightly controlled by various mechanisms to ensure the fidelity of DNA replication, including the exonuclease proofreading domains of the DNA polymerases encoded by the genes POLD1 and POLE, and the mismatch repair (MMR) 1.
• Another study also supports the idea that DNA replication occurs in the S phase, as it mentions that during S phase of the cell cycle, DNA is synthesized and subsequently divided between the daughter cells 1. However, the most recent and highest quality study 1 provides the most relevant information for determining the correct answer. Therefore, the correct answer is (c) S phase, as it is the phase where DNA replication occurs, ensuring that each daughter cell receives a complete set of genetic information.

From the Research

Cell Cycle Phases and DNA Replication

• The cell cycle is composed of several phases, including G1, S, G2, and M phases.
• DNA replication is a critical process that occurs during the cell cycle, and its timing is tightly regulated.

DNA Replication Phase

• According to studies 2, 3, 4, DNA replication occurs primarily during the S phase of the cell cycle.
• The S phase is characterized by the initiation and completion of DNA replication, ensuring that the entire genome is duplicated exactly once without errors.
• The regulation of DNA replication during the S phase involves the coordinated action of numerous factors, including origin licensing, replication proteins, and checkpoint pathways 2, 3.

Other Cell Cycle Phases

• The G1 phase prepares the cell for DNA replication by licensing origins and assembling prereplicative complexes 3.
• The G2 phase checks for errors and prepares the cell for mitosis, but it is not the primary phase for DNA replication 5, 6.
• The M phase is characterized by cell division and the separation of replicated chromosomes, but it is not the phase where DNA replication occurs 5, 6.

Exceptions and Additional Considerations

• Some studies suggest that parts of the genome may be replicated in G2 or mitosis, or even in the next G1 or S phase, to ensure genome integrity 6.
• However, the majority of DNA replication still occurs during the S phase, making it the correct answer to the question.