Molecular mechanisms regulating the cell cycle and their significance in pathological processes

The cell cycle is a tightly coordinated sequence of events that enables cellular growth, DNA replication, chromosome segregation, and division. Its fidelity depends on cyclin-dependent kinases (CDKs), cyclins, checkpoint proteins, ubiquitin-mediated proteolysis, and DNA-damage response pathways. This narrative review synthesizes established molecular mechanisms governing the G1/S, intra-S, and G2/M transitions and examines their disruption in cancer, developmental disorders, and tissue degeneration. Particular attention is paid to the RB–E2F axis, p53–p21 signaling, ATM/ATR checkpoint pathways, and the anaphase-promoting complex/cyclosome. Understanding these interconnected mechanisms helps explain uncontrolled proliferation, genomic instability, and cellular senescence, while identifying potential therapeutic targets. The review is based on published scientific literature and does not report original experimental results.