Lecture Notes: The Cell Cycle

Introduction

• Importance of the Cell Cycle
  • Series of phases and steps for cell replication
  • Controls cell growth
  • Main phases: Interphase and Mitosis
  • Related topics in other videos: regulation, proto-oncogenes, tumor suppressor genes, DNA repair enzymes

Basics of a Cell

• Definition: Basic unit of all living things
• Components of a Eukaryotic Cell:
  • Cell Membrane: Phospholipid bilayer
  • Nucleus: Contains genetic material (DNA as chromatin)
  • Cytoplasm: Fluid inside the cell

Overview of the Cell Cycle

• Purpose: Replicate cells to make two identical diploid cells (2n = 46 chromosomes)

Interphase

• Components:
  • G1 Phase (Gap 1):
    • Increase number of organelles
    • Synthesize proteins and enzymes for DNA replication
    • Repair thymine dimers
    • Most cells exist in this phase
  • Types of cells:
    • Labile (proliferative) cells: Constantly in cycle (e.g., skin, GI tract, hematopoietic stem cells)
    • Stable (resting) cells: Enter cycle with stimulus (e.g., liver, kidney tubules)
    • Permanent cells: Never re-enter cycle (e.g., neurons, cardiac muscle)
  • S Phase (Synthesis):
    • DNA replication (semi-conservative model)
    • DNA polymerase types 1 and 3 ensure fidelity of replication
    • Takes about 6 hours
    • G1/S checkpoint to ensure DNA integrity
  • G2 Phase (Gap 2):
    • Cell grows in size, increases cytoplasm
    • Prepares for mitosis

Mitosis (M Phase)

• Phases:
  • Prophase:
    • Chromatin condenses into chromosomes
    • Nuclear envelope dissolves
    • Formation of microtubule organizing centers (centrioles)
  • Metaphase:
    • Chromosomes align at metaphase plate
    • Microtubules attach at kinetochores
  • Anaphase:
    • Sister chromatids separate and move to opposite poles
    • Motor proteins (dynein, kinesin) aid movement
  • Telophase:
    • Chromosomes reach poles and de-condense
    • Nuclear envelope re-forms
    • Cleavage furrow forms, leading to cytokinesis
    • Cytokinesis: Physical separation of cytoplasm into two cells

Regulation and Checkpoints

• Checkpoints:
  • G1/S, G2/M, and Metaphase (M) checkpoints ensure cell cycle accuracy
  • Checkpoints involve different proteins and genes

Additional Concepts

• Aging and Cell Cycle:
  • Telomeres shorten with age, leading to cell senescence
  • Permanent cells do not re-enter the cycle

Summary

• The cell cycle is crucial for cell replication and growth
• Involves tightly regulated phases and checkpoints
• Different types of cells have different propensities to enter the cycle

Conclusion

• Understanding the cell cycle is essential for grasping how cells function and replicate
• Further studies can explore the regulation and implications of cell cycle errors