MCAT Content / Mitosis / Growth Arrest

Growth arrest

Topic: Mitosis

Growth arrest or G0 is viewed as either an extended G1 phase, where the cell stops growing (in M phase) due to mutation/damage, due to contact inhibition (crowding), or lack of food.

Not all cells adhere to the normal cell cycle pattern in which a newly-formed daughter cell immediately enters the interphase, closely followed by the mitotic phase. Cells in G0 phase are not actively preparing to divide. The cell is in a quiescent (inactive) stage that occurs when cells exit the cell cycle. Some cells enter G0 temporarily until an external signal triggers the onset of G1. Other cells that never or rarely divide, such as mature cardiac muscle and nerve cells, remain in G0 permanently.

The cell cycle is shown in a circular graphic, with four stages. The S stage accounts for about 40 percent of the cycle. The G2 stage accounts for about 19 percent. Mitosis accounts for 2 percent, and G1 accounts for 39 percent. An arrow is shown exiting the G1 stage that points to the G0 stage outside the circle, in which cells are not actively dividing. Another arrow points from the G0 stage back into the G1 stage, where cells may re-enter the cycle.


Key Points

• Cells that are not actively preparing to divide enter an alternate phase called G0.

• G0 is a temporary condition until triggered to enter G1, while some remain in G0 permanently.


Key Terms

quiescent: in a state or period of inactivity or dormancy
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