G1 phase

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The G₁ phase is a period in the cell cycle during interphase, before mitosis ,cytokinesis, and the S phase. For many cells, this phase is the major period of cell growth during its lifespan. During this stage new organelles are being synthesized, so the cell requires both structural proteins and enzymes, resulting in great amount of protein synthesis. The metabolic rate of the cell will be high. G₁ consists of four subphases:

Competence (g1a)
Entry (g1b)
Progression (g1c)
Assembly (g1d)

These subphases may be affected by limiting growth factors, nutrient supply, and additional inhibiting factors.

A cell may pause in the G₁ phase before entering the S phase and enter a state of dormancy called the G₀ phase. Most mammallian cells do this.

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