cell-cycle-sim is a free educational simulator that renders the eukaryotic division cycle (G1 → S → G2 → M → G0) as a five-node graph, four Cyclin/CDK (D-E-A-B) Gaussian activation curves, and three checkpoint branches (G1/S p53-p21-Rb / G2/M Wee1-Cdc25-MPF / SAC BubR1-Mad2-Cdc20-APC/C). Human somatic 18-24h baseline, in-house React state machine, in-house SVG (zero Framer Motion / D3 / GSAP).

(1) Address HHMI BioInteractive (English-only), Khan Academy (static video), and textbook diagram limits with a ko/en/ja interactive entry (2) Undergraduate molecular/cell biology baseline (Alberts Ch.17 / Cooper Ch.16) (3) Learn checkpoint branching scenarios (DNA damage → p53-p21 → G1/S block, SAC active → M-phase arrest) (4) Dynamic Cyclin/CDK activation curves (four-pair Gaussian peak timing aligned to phase boundaries) (5) Zero external npm libs — Framer Motion 50 KB / D3 / GSAP all replaced by in-house stack

① Click any of the five phase nodes (G1 / S / G2 / M / G0) → phase description + key molecules (cyclin/CDK/p53/Rb) highlighted ② Auto-play ▶ / ⏸ + speed slider (0.5× / 1× / 2×) → 24h baseline time evolution ③ Inspect the four Cyclin/CDK Gaussian peaks — D (G1) / E (G1/S boundary) / A (S/G2) / B (M) ④ Checkpoint simulations: • G1/S: toggle DNA damage → p53 active → p21 → Rb phosphorylation blocked → no S entry • G2/M: Wee1 active → CDK1 Tyr15 phospho → MPF inactive / Cdc25 → active • SAC: kinetochore unattached → Mad2-BubR1 → Cdc20 inhibited → APC/C inactive → M-phase arrest ⑤ Hover any of 16 academic terms (cyclin / CDK / checkpoint / restriction point / SAC / cytokinesis / kinetochore / spindle, etc.) ⑥ First-visit IntroAnimation (sessionStorage `bp_intro_shown_cell-cycle-sim`)

Example 1) Normal 24h cycle (auto-play) — Cyclin D peak t≈4h / E peak at G1/S boundary t≈12h / A peak S/G2 / B peak M Example 2) DNA damage scenario — toggle damage in G1 → p53 → p21 → CDK2 inhibited → no S entry (G1 arrest) Example 3) SAC active scenario — kinetochore unattached in M → Mad2/BubR1 → Cdc20 inhibited → no cytokinesis (M arrest) Example 4) Quantitative comparison — toggle Wee1 / Cdc25 activity → MPF activation branches (whether G2 → M transition occurs)