Organelles in Eukaryotic Cells: Vacuole, Lysosomes, and Microbodies

Vacuoles

• Structure: Membrane-enclosed organelles with a phospholipid bilayer.
• Location: Found in plant, fungal, and to some extent, animal cells.
• Functions in Plant Cells:
  • Water Storage: Stores water for cellular use.
  • Hydrostatic Pressure: Maintains turgor pressure, helping cells resist external forces.
  • Acidic Environment: Supports hydrolytic enzyme activity to break down macromolecules and waste products.
• Functions in Animal Cells:
  • Smaller in size compared to plant vacuoles.
  • Aid in endocytosis (cell engulfing extracellular material) and exocytosis (cell expelling waste).

Lysosomes

• Structure: Spherical, membrane-enclosed organelles.
• Location: Primarily found in animal cells, but recent evidence suggests presence in plants too.
• Function:
  • Contain an acidic environment (pH 4.8-5) for acid hydrolase enzymes.
  • Break down macromolecules: lipids, proteins, nucleic acids, carbohydrates.
  • Can destroy the cell through autolysis if necessary (e.g., damaged DNA).
  • Involved in immune responses by fusing with phagosomes to destroy bacteria.
• Production:
  • Enzymatic proteins made in the rough ER, processed in the Golgi apparatus, and transported in vesicles.

Microbodies (Peroxisomes and Glyoxosomes)

• Structure: Small, spherical, membrane-enclosed organelles.
• Types:
  • Peroxisomes (found in both animal and plant cells):
    • Conduct oxidation-reduction reactions, producing hydrogen peroxide as a byproduct.
    • Break down fatty acids to create ATP and synthesize lipids like cholesterol.
    • Detoxify the cell from toxins and drugs (e.g., alcohol).
    • Proteins are synthesized in free ribosomes, not in the ER.
  • Glyoxosomes (specialized plant peroxisomes):
    • Found in germinating plant cells and fungi.
    • Convert fatty acids to sugar precursors before chloroplasts mature.

Key Differences and Functions

• Vacuoles:
  • Predominantly in plant cells.
  • Store water, maintain pressure, and breakdown waste.
• Lysosomes:
  • Mainly in animal cells with some occurrence in plant cells.
  • Break down macromolecules and participate in autolysis.
  • Synthesized in the rough ER.
• Microbodies (Peroxisomes/Glyoxosomes):
  • Found in both animal and plant cells.
  • Break down fatty acids and detoxify cells.
  • Proteins synthesized in free ribosomes.