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Cellular Reproduction Vocabulary

Cell Cycle Control System

  • Cell cycle must be controlled to ensure stages occur in order and continue only when the previous stage is successfully completed.
  • Cell cycle checkpoints delay the cycle until certain conditions are met.
    • G1 checkpoint: Cell committed to divide; can enter G0 if not passed; checks for proper growth signals and DNA integrity (apoptosis if repair impossible).
    • G2 checkpoint: Verifies DNA replication and repair of any DNA damage.
    • Mitotic stage checkpoint: Ensures all chromosomes are attached to the spindle between metaphase and anaphase.

Cell Cycle Signals

  • Signals (molecules) stimulate or inhibit cell events.
    • External signals: Growth factors, hormones, contact inhibition.
    • Internal signals: Kinases and cyclins.

Internal Check Point Signals

  • Kinases: Enzymes that transfer a phosphate from ATP to other molecules, acting as an on/off switch.
    • Active in nuclear membrane removal and chromosome condensation.
  • Cyclins: Internal signals present during specific cell cycle stages.
    • Proper cyclin levels are needed for progression from G1 to S phase and G2 to M phase.
    • Cyclin destruction is necessary for normal cell cycle progression.

External Check Point Signals

  • Stimulate cells to proceed through the cell cycle.
    • Epidermal growth factor (EGF) stimulates skin repair.
    • Estrogen stimulates uterine lining division.
  • Contact inhibition: Cells stop dividing when they touch.
  • Telomeres: Repeating DNA sequences (TTAGGG) at chromosome ends that promote chromosome stability.
    • Telomere shortening leads to cell aging and apoptosis.

Apoptosis

  • Programmed cell death triggered by internal or external signals.
  • Maintains appropriate cell numbers and is a normal part of development.

Cell Cycle and Cancer

  • Cancer results from cell cycle dysregulation due to mutations.
  • Cancer is a genetic disease involving uncontrolled cell reproduction.

Proto-oncogenes and Tumor Suppressor Genes

  • Proto-oncogenes: stimulate cell division and prevent apoptosis; mutation leads to oncogenes, accelerating cell division.
  • Tumor suppressor genes: inhibit cell division and promote apoptosis; mutation leads to uncontrolled cell division.

Other Genetic Changes and Cancer

  • Absence of telomere shortening can lead to chromosome instability.
  • Chromosomal rearrangements (translocations) can occur.
  • Other genes associated with cancer:
    • BRCA1 and BRCA2: Tumor suppressor proteins that repair DNA.
    • Retinoblastoma (RB) gene: Tumor suppressor; produces pRB protein.
    • RET gene: Proto-oncogene; predisposes to thyroid cancer.

Characteristics of Cancer

  • Carcinogenesis is slow and gradual.
  • Cancer cells:
    • Lack differentiation.
    • May be immortal.
    • Have abnormal nuclei and chromosome numbers.
    • Do not undergo apoptosis.
    • Form tumors and ignore inhibitory signals.
    • Undergo metastasis (spread) and angiogenesis (new blood vessel formation).

Cancer Cells

  • Benign tumors: Contained within a capsule.
  • Malignant tumors: Invasive and can spread.

Cancer Treatment

  • Aims to remove tumors or interfere with cancer cell reproduction.
    • Radiation therapy: Kills cells in a specific tumor by damaging DNA.
    • Chemotherapy: Kills cells throughout the body by damaging DNA or mitosis.
    • Hormone therapy: Prevents cells from receiving growth signals.

Prevention of Cancer

  • Avoid smoking and excessive sun exposure.
  • Moderate alcohol consumption.
  • Maintain a healthy diet with vitamins A and C, and include cabbage family vegetables.