The cell cycle has two phases, Interphase, and mitotic phases.
The interphase is divided into three phases:
G1: During this phase, the cell grows, copies the organelles, and synthesizes all necessary molecules for cell division.
→ Before passing to the next phase, it passes through a checkpoint. If the cell hasn't grown big enough or if there aren't enough proteins for the synthesis phase, then the cell goes back to G0 (resting phase)
S: This is the second phase of the interphase, during this phase, the cell copies the DNA and synthesizes a new double helix, the centromeres are also duplicated in this phase.
At the end of this phase, the cell has two identical copies of DNA.
G2: This is the last phase of the interphase. During this period the cell grows larger and reorganizes the cell contents (organelles, proteins, cytoskeleton) in preparation for the cell division.
→ Before passing to the next phase, there is a second checkpoint. It checks if the DNA was copied correctly, if there are errors on the copied DNA, the cell does not proceed with the rest of the cycle. During this period the cell also checks if it has grown properly, if the size is not enough, the division stops.
Mitotic phase (M)
After the preparation for cell division is over, the cell is ready to duplicate. During this phase occurs mitosis followed by cytokinesis.
→ The process of mitosis has 4 phases: Prophase, Metaphase, Anaphase, Telophase. During the Metaphase occurs the last checkpoint of the cell cycle, before continuing with the process the cell checks if the chromosomes are properly attached to the spindle.
After this phase, there are two daughter cells, these cells enter that resting phase G0.
During this phase, the cell is not actively preparing to divide. It just carries on with its other functions.