Final answer:
The Go phase is an inactive phase in the cell cycle where cells are not preparing to divide. Cells enter this phase temporarily due to environmental cues or permanently in the case of specialized cells like nerve and cardiac muscle cells. The cell growth checkpoint ensures cells only divide when ready.
Step-by-step explanation:
Not every cell follows the conventional cell cycle of progressing from formation straight into interphase and then mitosis. The Go phase is a distinct phase in the cell cycle where cells are not preparing to divide and are in a quiescent (inactive) state. Cells may enter the Go phase temporarily due to lack of nutrients or absence of growth factor signals, subsequently waiting until conditions improve to progress to G1 phase. Conversely, some cells, like those found in mature cardiac muscle and nerve tissue, enter the Go phase permanently because they do not divide again, fulfilling specialized roles for the duration of their existence.
During the cell growth checkpoint toward the end of G1, the cell is evaluated for sufficient size and protein synthesis needed for division. If not ready, the cell will enter the Go phase until conditions are favorable. This process ensures that cell division only occurs when the cell is adequately prepared, thereby maintaining proper cell function and tissue health. Cells in the Go phase can be either temporarily paused in the cycle or have reached a state of terminal differentiation, in which they no longer cycle and remain in Go, focusing on performing specific functions for the body.