Lecture Notes: Cell Theory and Transport Mechanisms

Introduction to Cell Theory

• Cells are considered alive.
• Observation of single-cell organisms shows they maintain life processes.

Maintaining Homeostasis

• Essential for cells to move objects in and out to maintain homeostasis.

Diffusion

• Simple method for movement of molecules like oxygen and carbon dioxide.
• Key Principle: Movement from high concentration to low concentration ("high to low is the only way to go").
• Cell Membrane:
  • Structure: Phospholipid bilayer.
  • Components: Polar head and non-polar tail.
• Passive Movement: Does not require energy.
• Concentration Gradient: Diffusion occurs along with the concentration gradient.

Facilitated Diffusion

• Requires a channel or protein to help move particles.
• Example: Glucose uses a carrier protein to cross the membrane.
• Energy Requirement: No ATP required.

Active Transport

• When Needed: For moving objects too large or against the concentration gradient.
• Energy Requirement: Uses ATP.

Types of Active Transport

1. Membrane Pumps

   • Move substances against concentration gradient (low to high concentration).
   • Example: Sodium-Potassium Pump:
     • 3 sodium ions attach to carrier protein.
     • ATP attaches, changes protein shape, sodium exits cell.
     • 2 potassium ions attach, phosphate detaches, changes shape, potassium enters cell.

2. Vesicle Movements

   • Endocytosis:
     • Moves larger objects into the cell by engulfing.
     • Types of Endocytosis:
       • Phagocytosis: Ingestion of solids.
       • Pinocytosis: Ingestion of liquids.
       • Receptor Mediated Endocytosis: Specific molecules captured by receptor proteins trigger vesicular uptake.
   • Exocytosis:
     • Expelling objects out of the cell.
     • Objects encased in vesicles are released outside.

Conclusion

• Active and passive transport mechanisms are vital for cellular function and homeostasis.
• Further resources available for deeper understanding, such as playlists on active transport.