Notes on the Origins of Life and Cell Theory

Introduction to Spontaneous Generation

• Historical Context: In Aristotle's time, it was commonly believed that non-living matter could spontaneously generate life.
• Examples of Spontaneous Generation:
  • Mice appearing in grain silos thought to arise from non-living materials.
  • Aristotle’s belief that semen enlivened menstrual blood to create babies.
• Modern Understanding: Life does not spontaneously arise from inorganic materials; it is composed of cells.

Advancements in Cell Theory

• Robert Hooke (1665):
  • Improved microscopes, discovered cells in cork.
  • Named 'cells' due to resemblance to monks' rooms.
• Key Contributions from Other Scientists:
  • Theodore Schwann & Matthijs Schleiden (Mid-1800s): Proposed all organisms are made of cells; cell as the basic building block of life.
  • Rudolf Virchow (1855): Proposed that all cells come from pre-existing cells.
• Classical Cell Theory: Formed by these three foundational ideas.

Types of Cells

• Prokaryotic vs. Eukaryotic Cells:
  • Eukaryotic Cells: Have a defined nucleus; more complex. Common in plants, animals, fungi.
  • Prokaryotic Cells: Lack a nucleus ("pre-nucleus"), simpler structure. Example: E. coli.
• Evolution: Eukaryotic cells are believed to have evolved from prokaryotic cells about 2.7 billion years ago.

Structure of Eukaryotic Cells

• Components of Plant Cells:
  • Cell Wall: Provides structure; made of carbohydrates and proteins.
  • Central Vacuole: Stores water and chemicals, providing support.
  • Chloroplasts: Convert sunlight into usable energy (unique to plant cells).
• Components of Animal Cells:
  • Cell Membrane: Lipid barrier surrounding the cell.
  • Nucleus: Contains genetic material (RNA is sent out for protein production).
  • Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; Smooth ER synthesizes lipids, including hormones.
  • Golgi Apparatus: Packages proteins into vesicles for distribution.
  • Mitochondria: Power plants of the cell, producing energy.

Endosymbiotic Theory

• Origin of Mitochondria and Chloroplasts:
  • Hypothesized that these organelles originated from a symbiotic relationship between two bacteria.
  • Endosymbiosis theory popularized by Dr. Lynn Margulis in the 1960s, supported by advancements in microscopy.

Modern Cell Theory

• Building on Classical Cell Theory:
  • Modern cell theory includes:
    • Energy flows within cells.
    • Similar species have similar cells.
    • Cells divide and pass genetic information to new cells.
• Importance of Microscopy: Modern advancements in microscopy have been crucial in understanding cell structure and function.

Size and Structure of Cells

• Cell Size Limitations:
  • Surface area to volume ratio limits cell size; larger cells face challenges in maintaining efficiency.
  • Some cells adapt by changing shape (e.g., Caulerpa taxifolia).

Conclusion

• Scientific Iteration: The history of cell discovery demonstrates how science builds upon previous knowledge.
• Importance of Curiosity: Asking "Why did that happen?" leads to discoveries in cell theory and our understanding of life.
• Next Topic: Upcoming lecture will cover cellular membranes.