Cancer and cell regulation

Notes on Cell Division, Regulation, and Related Issues

How Cells Know When to Divide

  • Controlled Division: Cell growth and division in multicellular organisms are tightly regulated to ensure orderly growth and development. 

  • Disrupted control of the cell cycle can lead to serious diseases like cancer.

  • Different types of cells divide at different rates: 

    • Muscle and nerve cells: Rarely divide after development. 

    • Skin, digestive tract, and bone marrow cells: Divide regularly to replace worn-out or damaged cells.




Controls on Cell Division

  • Contact Inhibition:

    • In laboratory experiments, cells divide until they come into contact with one another. 

    • Cells stop dividing upon contact but can begin dividing again if neighboring cells are removed or disrupted. 

    • This ability to turn growth controls on and off regulates cell behavior during healing.

  • Injury and Healing:

    • Injuries like cuts or broken bones stimulate rapid cell division at the edges of the injury. 

    • Once the healing process nears completion, cell division slows, and normal regulation is restored.




Regulatory Proteins and the Cell Cycle

  1. Internal Regulators:

    • Proteins that respond to events inside the cell and act as checkpoints. 

    • Example: 

      • A checkpoint ensures that mitosis does not occur until chromosomes are fully replicated. 

      • Another checkpoint prevents anaphase until spindle fibers attach to chromosomes.

  2. External Regulators:

    • Respond to external events and direct cells to either speed up or slow down the cell cycle. 

    • Growth Factors: External proteins that stimulate cell growth and division, crucial for embryonic development and wound healing. 

    • Other external regulators, like those on neighboring cells, slow or stop cell cycles to prevent excessive growth and tissue disruption.




Cyclins: The Discovery of Cell Cycle Regulators

  • In the 1980s, scientists identified the first regulatory protein that controls the cell cycle. 

  • Named cyclins, these proteins regulate the timing of the cell cycle in eukaryotic cells. 

  • Cyclins follow cyclical patterns, rising and falling throughout the cycle.




Apoptosis: Programmed Cell Death

  • Definition: A controlled process where cells are triggered to self-destruct. 

  • Process: 

    • Chromatin shrinks, and parts of the cell membrane break off. 

    • Neighboring cells clean up remnants.

  • Role in Development: Shapes tissue and organ structures. 

  • Diseases Associated with Dysregulated Apoptosis:

    • Too much apoptosis: Seen in conditions like AIDS and Parkinson’s disease.

    • Insufficient apoptosis can prevent the removal of dangerous or damaged cells.




Cancer: Uncontrolled Cell Growth

  1. What is Cancer?

    • A disorder where cells lose the ability to regulate growth. 

    • Cancer cells ignore regulatory signals, disrupting the cell cycle and leading to uncontrolled division.

  2. Tumors:

    • Benign Tumors: Noncancerous and do not spread. 

    • Malignant Tumors: Cancerous; invade and destroy nearby tissue, disrupt body functions, and metastasize (spread to other areas).

  3. Impact:

    • Cancer cells absorb nutrients, block nerve functions, and prevent proper organ functioning. 

    • This disrupts the body's balance, causing life-threatening illnesses.

  4. Causes of Cancer (Details not included in the text beyond mentioning defect origins).