period between mitosis events (3 stages)

                   G₁ stage-cell grows in size and the organelles increase in number

                   S stage – DNA synthesis occurs (sister chromatids are formed)

                   G₂ stage – cell prepares for mitosis

M stage – mitosis (nuclear division)  and cytokinesis  (division of the cytoplasm.

Control of the Cell Cycle

certain types of cells continually divide, while others are arrested in the G₁ and G₂ phase

-There are three regulatory check points the cells must move through for cell division to occur

G₁ stage -------->  S stage

G₂ stage---------> M stage

M checkpoint

Enzymes know as cyclins and kinases regulate the passage of cells through these checkpoints

enzymes that remove phosphate from ATP and put it on another protein

S stage, when S-cyclin  combines with S-kinase, the kinase can then phosphorylate a protein that allows the cell cycle to continue.

M stage, when M-cyclin  combines with M-kinase, the kinase can then phosphorylate a protein that allows the cell cycle to continue.

Failure to regulate the cell cycle  can result in uncontrolled cell division-Cancer