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G1 phase (or post-mitotic phase) is one of the four phases of the cell cycle and occurs in stage one of interphase. G stands for Gap and the 1 represents first so the G1 phase is the first gap phase. During this phase, the cell increases in mass carrying out protein synthesis and other cellular functions, ecxcept DNA replication. This phase includes the G1 checkpoint which is an important control point in the cell cycle. During this checkpoint the cell normally becomes committed to DNA synthesis. However, it can enter a quiescent resting state, G0, a paused stage where they can then enter G1. The chromosomes each contain only one molecule of DNA and are not visible [1]

It is contolled by activity of cyclin-dependent kinases [2].


  1. Interphase website http://biology.uoregon.edu/reference/ort_mitosis/interphase.html
  2. Bruce Alberts, 2008, Molecular biology of the cell, 5th edition, New York, Garland Science
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