How Do Cells Know to Move to the Next Step?

• Differential coexpression of Cyclins and Cyclin Dependent Kinases (CDKs) proteins control cell progression through the Cell Cycle at each of three checkpoints

• Growth factors signal the cell to produce checkpoint-specific cyclin proteins

• Cyclin proteins produced via protein synthesis build up in the cell

• At high enough concentrations, cyclin binds to its specific Cyclin Dependent Kinase enzyme

• CDK initiates the phosphorylation cascade that allows the cell to pass the checkpoint and continue the cell cycle

Cell Cycle Control Overview

• Cells are required to pass through 3 checkpoints as they progress through the cell cycle

• Cells check for damage, mutations, and proper internal conditions for each checkpoint

• Healthy cells complete the cell cycle

• Damaged/mutated cells center cell cycle arrest

  • Cell produces inhibitors of cyclin proteins to prevent progression through the cell cycle

What SHOULD Happen Next?

• Repairable:

  • The damaged DNA is repaired and continues through the cell cycle, eventually producing two genetically identical daughter cells

  • Cells must pass all 3 checkpoints to complete the cell cycle

• Irreparable:

  • Cell goes through programmed cell death (apoptosis) and is eliminated, no daughter cells are produced, diseases like cancer are prevented

Cancer: A Disease of the Cell Cycle

• Cancer is uncontrolled cell growth leading to tumors

• Cancer cells have an accumulation of mutations in genes (p53) that prevent damaged cells from continuing through the cell cycle

• These mutations prevent programmed cell death and allow the cancer cell to grow and divide unlimitedly