G1 phase of the cell cycle (G1 phase)

The **G1 phase** ("Gap 1" or "Growth 1") is the first stage within interphase of the eukaryotic cell cycle. During this period, cells grow in size and synthesize mRNA and proteins necessary for subsequent DNA replication. The duration and regulation of G1 are critical because they determine whether a cell will proceed to divide or exit into quiescence (G0). Key molecular events include activation/inhibition of cyclin-dependent kinases (CDKs), accumulation of cyclins such as cyclin D and E, phosphorylation status changes in retinoblastoma protein (Rb), and integration of signals from growth factors or stress responses. The transition from G1 to S ("start" or restriction point) is tightly regulated; dysregulation at this checkpoint can lead to uncontrolled proliferation characteristic of cancer. While many therapeutic agents target proteins that regulate passage through the G1/S checkpoint—such as CDK inhibitors—the "G1 phase" itself is not a discrete molecular target but rather a functional state defined by cellular activities.[1][3][4] --- **Note:** There is something incorrect about using “Cell cycle at G1 phase” as a therapeutic target name—it refers to an entire cellular state/process rather than any single molecule/receptor/enzyme typically considered druggable targets.[6] For structured data purposes, it should be mapped instead to specific regulatory molecules active during this period such as “Cyclin-dependent kinase 4” or “Retinoblastoma-associated protein.”

Other names

Gap 1 phaseGrowth 1 phaseFirst gap phasePre-DNA synthesis phase