Cell Cycle Checkpoints Part 1

Introduction to Cell Cycle Checkpoints

Discusses the importance of understanding the cell cycle to comprehend cell cycle checkpoints.
Warm-up question highlights the behavior of DNA during M phase, confirming knowledge of mitosis.
Key Concept: During M phase, the amount of DNA is halved as the cell divides into two daughter cells.

The lesson focuses on how the cell cycle is regulated to prevent uncontrolled cell division, which can lead to cancer.
Example: Recovery from an ulcer requires cessation of cell division to prevent excessive cell growth that may cause cancer.
Mechanisms include both internal and external signals that influence cell behaviors during the cycle.

Growth Factors:
- Substances that bind to cell surface receptors to trigger internal signaling processes that regulate cell division.
- Familiar within signal transduction pathways.
Density-dependent Inhibition (Contact Inhibition):
- Cells stop dividing when they come into contact with neighboring cells, signifying sufficient cell population.
Anchorage Dependence:
- Cells must be attached to a substrate to grow and divide, limiting growth to appropriate locations.

Normal cell division includes regulated pauses between phases of the cell cycle.
Cancerous cell division occurs more rapidly and is less controlled, leading to tumor formation due to lack of pauses.

Growth factors bind to receptor proteins on the plasma membrane;
- Initiate a signal transduction pathway; changes receptor shape to trigger cellular responses.
- In cancer, cells may enter Autocrine Signaling:
  - Cancer cells produce their own growth factors and self-stimulate division.
- Increased gene amplification can occur, where cancer cells generate more receptors, becoming overly responsive to growth signals.

Ligands binding to receptors lead to changes that ultimately signal for cell proliferation.
Mutations in signaling pathways can cause:
- Increased transcription of growth factors or receptors.
- Increased sensitivity to growth signals, which can promote uncontrolled cell division.

Contact inhibition halts cell division when cells touch each other, signaling population density.
Cells utilize receptors (like CAM proteins) to detect neighboring cells.
Over-cell proliferation can create scars or tumors if regulatory mechanisms fail.

When cells are dividing, CAM proteins interact with signaling proteins like Ras to promote division.
In the presence of surrounding cells, CAM proteins recruit M factors to inhibit Ras, preventing further division.
Mutations in M proteins can disrupt this process, leading to continual mitosis and potential cancer development.

The lesson emphasizes understanding the roles and mechanisms of various factors in cell regulation.
The importance of checkpoints in preventing cancerous growth is highlighted.