Lecture Notes: Cell Structure and Transport Mechanisms

Introduction to Cells

• Common Structures: Genetic material, cytoplasm, ribosomes
  • Found in both prokaryotes and eukaryotes.
• Eukaryote Specifics: Membrane-bound organelles, More complex and bigger than prokaryotes.

Homeostasis and the Cell Membrane

• Homeostasis: Maintaining a stable internal environment.
• Cell Membrane: Critical for regulating homeostasis by controlling entry and exit of substances.
  • Made of a phospholipid bilayer
    • Polar head and nonpolar tail.
• Transport through Membrane:
  • Simple Diffusion: Movement of small, nonpolar molecules (e.g., oxygen, carbon dioxide) through the bilayer without energy (passive transport).
  • Facilitated Diffusion: Requires transport proteins; still passive transport.
    • Moves with concentration gradient (high to low).
    • Examples: Charged ions, glucose, water (through aquaporins).

Types of Transport

Passive Transport

• Characteristics: No energy required, moves with concentration gradient.
• Examples:
  • Simple diffusion.
  • Facilitated diffusion through transport proteins.

Active Transport

• Characteristics: Requires energy (ATP), moves against concentration gradient (low to high).
• Example:
  • Sodium-Potassium Pump: Uses ATP to move ions.
  • Endocytosis: Cell engulfs substances to bring inside (types include phagocytosis, pinocytosis, receptor-mediated endocytosis).
    • Endocytosis Types:
      • Phagocytosis: Engulfs large particles.
      • Receptor-Mediated: Specific substances bind to receptors.
      • Pinocytosis: Ingestion of liquid.
  • Exocytosis: Releases substances from cell, important for waste removal and secretion of materials like polysaccharides for plant cell walls.

Summary

• Membrane Transport Mechanisms: Crucial for maintaining homeostasis and allowing cells to interact with their environment.
• Energy Use in Cells: Differentiates passive from active transport mechanisms.

Conclusion

• Encouragement to explore further on different endocytosis types and cellular mechanisms.
  • The importance of curiosity in learning about cellular biology.