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.