Explain The p53 pathway is part of the G1-to-S checkpoint?

As with most body processes, the cell cycle is highly regulated to prevent mutated cell synthesis and uncontrolled cell division leading to tumor formation.[10] The cell cycle control system is biochemically based so that mitosis-promoting factor (MPF) proteins control the transition from one stage to the next based on a series of checkpoints.MPF is a protein dimer consisting of cycline and cycline-dependent kinase (Cdk), serine and threonine kinase, which come together at various points of the cycle to control the progression of cells through the cycle. When cycline binds to Cdk, Cdk becomes activated and phosphorylates serine and threonine on other proteins causing other proteins to activate and degrade, allowing the cell to transition