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DNA Synthesis During S Phase of Interphase Explained for Certification
S phase of the cell cycle handles DNA replication semiconservatively with polymerases and checkpoints—not G1, G2, or M—essential mechanism for genetic fidelity in mitosis, key for General Biology exam mastery.
Question
Which phase of the cell cycle is characterized by the replication of DNA?
A. G1 phase
B. G2 phase
C. S phase
D. M phase
Answer
C. S phase
Explanation
The S phase, or synthesis phase, occurs during the eukaryotic cell cycle’s interphase where DNA replication precisely duplicates the entire genome, ensuring each daughter cell receives identical genetic material during mitosis; this process involves origins of replication firing to unwind double helices via helicases, primase laying RNA primers, DNA polymerases (e.g., pol δ/ε) synthesizing new strands semiconservatively (leading continuously, lagging via Okazaki fragments), and ligase sealing nicks, all under tight regulation by cyclin-CDK complexes and checkpoints to prevent errors like under- or over-replication. G1 phase prepares for replication by growing the cell and synthesizing enzymes/checkpoint proteins, G2 phase verifies DNA integrity post-replication while completing protein synthesis for mitosis, and M phase executes mitosis (nuclear division) and cytokinesis (cytoplasmic division), none of which replicate DNA itself.