Cells go through periods of growth and division. Cell division occurs during the Mitotic phase.

The rest of the cell cycle is called Interphase. This consists of the first growth phase, the synthesis phase, and the second growth phase.

The G1 phase, or First Growth Phase, is when growth and normal metabolic roles occur.

The S Phase, or DNA Synthesis phase, is when DNA replication occurs.

The G2 Phase, or Second Growth Phase, is when growth and preparation for mitosis occurs.

The M Phase, or Mitotic Phase, is when cell division occurs.

A checkpoint is one of several points in the eukaryotic cell cycle at which the progression of a cell to the next stage in the cycle can be stopped until conditions are favorable. The checkpoint acts the same as a security guard, preventing entrance to a hockey game until the line inside has dwindled down.

There are three checkpoints during the cell cycle.

1. The G1 checkpoint that checks for cell size, nutrients, growth factors, and DNA damage before allowing the cell to continue on towards DNA synthesis.

2. The G2 checkpoint which checks for cell size and DNA replication before allowing a cell to continue to Mitosis.

3. The Spindle Assembly Checkpoint which checks for chromosome attachment to the spindle before allowing a cell to continue to G1.

At any of the checkpoints, if a cell does not "pass inspection," it can be sent to a resting state, or G0. If the damage is in the DNA, a cell will attempt to repair the DNA damage. If this does not work, a cell can trigger cell death, or apoptosis.