Eukaryotic organelles

Cell Structures

• Cytoplasm: All cells contain cytoplasm.

• Cell Membrane: Universal structure present in all cells.

• Mitochondria: Found in all eukaryotic cells, including both plant and animal cells; important for energy production.

  • Mitochondria appear as small pink dots in cell diagrams.

Unique Structures in Plant Cells

• Chloroplasts:

  • Present in plant cells but absent in animal cells.

  • Function in photosynthesis, converting sunlight into energy.

• Vacuole:

  • Plant cells have a large central vacuole; animal cells do not.

  • Provides structural support and storage.

• Cell Wall:

  • Present only in plant cells, made primarily of cellulose.

  • Offers rigidity and strength, helping maintain plant structure.

Key Differences Between Plant and Animal Cells

• Plant cells possess:

  • Cell wall

  • Large permanent central vacuole

  • Chloroplasts

• Animal cells lack these structures but share other cellular components with plant cells.

Endosymbiotic Theory

• Definition: Theory suggesting that certain organelles (mitochondria and chloroplasts) in eukaryotic cells were once independent prokaryotic cells.

• Key Terminology:

  • Endo: Internal or within.

  • Symbiosis: A mutually beneficial relationship between two species.

• Proposed by Dr. Lynn Margulis, supported by decades of research.

• The theory represents a significant understanding of eukaryotic cell evolution.

Theoretical Background

• Early eukaryotic cells likely engulfed prokaryotic cells:

  • Oxygen-using prokaryotes: Efficient energy conversion.

  • Photosynthetic prokaryotes: Convert sunlight and CO2 into energy (glucose).

• Instead of being digested, these prokaryotes lived within early eukaryotic cells, becoming mitochondria and chloroplasts, respectively.

Supporting Evidence for Endosymbiotic Theory

1. Double Membrane:

   • Unique to mitochondria and chloroplasts, arising from engulfment (outer membrane from the eukaryotic cell and inner from the prokaryote).

2. DNA and Ribosomes:

   • Both organelles contain their own DNA and ribosomes, akin to prokaryotic characteristics.

   • Capable of producing their own proteins.

3. Replication:

   • Mitochondria and chloroplasts can grow and replicate independently within the cell, similar to prokaryotic division.

4. Size Comparison:

   • Similar in size to prokaryotic cells.

Conclusion

• Endosymbiotic theory is widely accepted as a scientific theory due to extensive supporting evidence.

• Mitochondria and chloroplasts are no longer capable of independent survival; they have evolved to rely on their eukaryotic host cells for survival.