Lecture on the Cell Cycle

Introduction

• The cell cycle is crucial for cell replication and controlling cell growth.
• Consists of interphase and mitosis.
• Regulation involves proto-oncogenes, tumor suppressor genes, and DNA repair enzymes.
• Focus of this lecture: phases of interphase and mitosis.

Basic Structure of a Eukaryotic Cell

• Components:
  • Cell membrane: Phospholipid bilayer.
  • Nucleus: Contains genetic material (chromatin).
  • Cytoplasm: Fluid where organelles reside.
• Aim: Duplicate the DNA in the nucleus.

Phases of the Cell Cycle

Interphase

• G1 Phase (Gap 1) or Gap 1 Phase:
  • Cell grows and increases organelles.
  • Synthesizes enzymes necessary for DNA replication.
  • Most cells spend the majority of the cell cycle in this phase.
  • Cell Types:
    • Labile (proliferative) cells: Constantly in the cell cycle (e.g., skin epithelium, GI tract).
    • Stable cells: Replicate when stimulated (e.g., liver hepatocytes).
    • Permanent cells: Do not replicate (e.g., neurons).
• S Phase (Synthesis Phase):
  • DNA replication occurs.
  • Transition from 2N (46 chromosomes) to 4N (92 chromosomes).
  • Lasts about 6 hours.
  • Ensures no replication errors occur.
• G2 Phase (Gap 2):
  • Cell growth continues.
  • Prepares for mitosis.
  • G2 phase lasts about 2 hours.

Mitosis (M Phase)

• Phases (PMAT):
  • Prophase:
    • Chromatin condenses into chromosomes.
    • Nuclear envelope dissolves.
    • Formation of microtubule organization centers (centrioles).
  • Metaphase:
    • Chromosomes align on the metaphase plate.
    • Polar microtubules attach to kinetochores.
    • Ensures proper alignment before separation.
  • Anaphase:
    • Sister chromatids separate to opposite poles.
    • Involves motor proteins (dynein and kinesin).
  • Telophase:
    • Chromosomes de-condense back to chromatin.
    • Nuclear envelope reforms.
    • Cytokinesis occurs (cytoplasm divides).

Cell Cycle Checkpoints

• G1/S checkpoint: Ensures cell is ready for DNA synthesis.
• G2/M checkpoint: Verifies all DNA has replicated correctly.
• M checkpoint: Ensures chromosomes are aligned before separation.

Special Considerations

• G0 Phase: Quiescent phase where cells can "rest."
• Aging and Telomeres: Telomeres shorten with age; affects cell's ability to replicate (cell senescence).

Conclusion

• Understanding the cell cycle is crucial for insights into cell replication and growth control.

Note: These notes provide a comprehensive overview of the cell cycle lecture, including terminology, phases, and important processes.