In-Depth Notes on Genetic Expression and Cancer

Introduction to Genetic Regulation

  • Genetic expression is modulated through various mechanisms.
  • Protein synthesis can be regulated from the genome, including chromatin modification.
  • External signals, such as growth factors, can initiate protein synthesis.

Growth Factors and Cell Division

  • Growth Factors: Signals from outside the cell prompting it to divide.
    • Example: A signal triggers mRNA transcription for cyclin.
  • Cyclin Role: When a cell receives a signal:
    • Increases cyclin production.
    • Cyclin binds to CDK (Cyclin-dependent kinase) to activate it and proceed with the cell cycle.

Cell Cycle Regulation

  • Not a simple on/off system; involves a cascade of signals.
  • Cyclins are produced in peaks and then degrade to prevent continuous activation of CDKs.
  • Different CDK-cyclin pairs regulate distinct phases of the cell cycle to avoid concurrent activation.

Checkpoint Mechanisms

  • G1 Checkpoint: Checks for nutrients, growth, and DNA integrity.
    • If conditions are unmet, cells enter phase G0, halting division.
  • p53 Protein: Key tumor suppressor that activates genes like p21 to inhibit CDKs if DNA damage is detected.
    • If DNA is unreparable, it triggers apoptosis (programmed cell death).

Cancer: Uncontrolled Cell Division

  • Cancer arises from uncontrolled cell growth, often due to damaged regulatory mechanisms.
  • *Tumor Types:
    • Benign tumors: Localized and usually removable.
    • Malignant tumors: Invade other tissues, spreading via blood or lymph.
  • Cancer cells may bypass damage checkpoints, allowing them to divide uncontrollably.

Role of p53 in Cancer

  • Normal p53 detects DNA damage, halting the cell cycle for repair or triggering apoptosis if irreparable.
  • Mutated p53 cannot function correctly, resulting in cells dividing despite damage, leading to cancer.
  • Mutagens: Environmental exposures (e.g., tobacco, UV light) can cause mutations in p53.
  • HPV: Associated with an increased risk of cancer, often by altering DNA of host cells and inhibiting p53 function.

Preventive Measures: Vaccines

  • HPV vaccine prevents several forms of cancer by averting the virus from inducing mutations in host DNA.
  • Early vaccination for optimal protection, recommended from ages 12 to 22.

Genes and Mutations in Cancer

  • Proto-oncogenes: Normal genes that can become oncogenes through mutation; they regulate cell cycle progression.
  • Cancer typically results from an accumulation of several mutations over time, not just a single change.

Treatment Strategies for Cancer

  • Treatment Modalities: Various therapies are designed to halt cell division:
    • Hormonal therapies.
    • Surgical removal of tumors.
    • Chemotherapy (e.g., paclitaxel disrupts mitotic spindle formation).
    • Targeted therapies (e.g., Herceptin blocks growth factor signals).
    • Radiation therapy induces DNA damage to trigger apoptosis in cancer cells.
  • Personalized Medicine: Tailoring treatment based on specific gene mutations in individual tumors to optimize efficacy.