Cell Organelles: Lysosomes and Peroxisomes

Lysosomes

• Definition: Membrane-bound organelles in cells.
• Function: Digest various molecules and substances within the cell.

Processes

1. Autophagy

   • Meaning: "Self-eating."
   • Function: Digests molecules that are part of the cell itself or from other cells.
   • Examples:
     • Digestion of non-functional organelles like old mitochondria.
     • Macrophages engulf bacteria/viruses, which are then digested.

2. Crinophagy

   • Function: Digests excess secretory products.
   • Example: Digestion of extra hormones produced by a cell.

Post-Digestion

• Lysosomes release broken-down building blocks into the cytoplasm for reuse.
• Example: Proteins digested into amino acids for further use.

Environment

• Enzymes: Acid hydrolases, requiring an acidic environment (pH ~5).
• Safety Mechanism: If lysosomes burst, enzymes won't function well in the neutral pH of cytoplasm (pH ~7.4).
  • However, if many lysosomes burst, cytoplasm might become acidic, risking organelle digestion.

Peroxisomes

• Function: Involved in various metabolic activities.
  • Lipid Breakdown: Important in some cells.
  • Detoxification: Helps liver cells detoxify chemicals and drugs.

Role in Hydrogen Peroxide Detoxification

• By-product: Hydrogen peroxide produced by various cell enzymes.
• Danger: Hydrogen peroxide is harmful to cells.
• Action: Isolates hydrogen peroxide in peroxisomes.

Enzyme

• Catalase: Breaks down hydrogen peroxide.
  • Reaction: Hydrogen peroxide + catalase → water + oxygen.

Protection

• Peroxisomes protect the cell by breaking down hydrogen peroxide into non-harmful substances (water and oxygen).