G1 is the cell growth phase where the cell accumulates nutrients and decide if it is going to undergo the cell cycle, as determined by the restriction point in G1. If the cell has insufficient nutrients or has not grown sufficiently to enter the cell cycle, it will remain in G1 or exit to G0 phase where it will not divide.
G2 occurs after S phase DNA replication in the cell cycle. In G2, the cell is growing and preparing for cell cycle by producing proteins required such as the centrosome.
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