Structure and Function of the Cell ✏ Biology In a Nutshell

Rucete ✏ Biology In a Nutshell

1. What is a Cell?

• The basic functional unit of all living organisms.
• Contains a plasma membrane, cytoplasm, and nucleus.

 

 

2. Plasma Membrane – Cell Boundary

• Function: Encloses the cell, separating the internal and external environments.
• Structure:
  • Phospholipid Bilayer:
    • Hydrophilic (water-attracting) heads face outward.
    • Hydrophobic (water-repelling) tails face inward.
  • Selective Permeability:
    • Allows small, uncharged, polar molecules and hydrophobic molecules to pass.
    • Blocks large polar molecules and ions from passing freely.
      

 

 

3. Cytoplasm & Cytosol

• Cytoplasm: Contains organelles, each with a specific function.
• Cytosol: The liquid portion of the cytoplasm, containing water, proteins, and nutrients.

 

 

4. Proteins in the Plasma Membrane

• Channel Proteins: Provide passage for polar or charged molecules.
• Ion Channels: Allow the movement of ions across the membrane.
• Porins: Specialized proteins that permit the passage of certain small polar molecules and ions.
• Aquaporins: Water channels that facilitate rapid water transport in some cells.
• Carrier Proteins: Bind to molecules to increase solubility and aid in transport.
• Transport Proteins: Use ATP energy to move substances across the membrane.
  • Example: Na⁺/K⁺ Pump – Uses ATP to maintain high Na⁺ and K⁺ concentration gradients.
• Recognition Proteins: Provide cell-specific identification.
• Adhesion Proteins: Help cells stick together.
• Receptor Proteins: Bind to hormones or trigger molecules for cell signaling.

 

 

5. Other Components of the Plasma Membrane

• Cholesterol: Found in animal cell membranes, providing structural stability.
• Glycocalyx: A carbohydrate layer covering the cell surface, involved in protection and recognition.

 

 

6. Fluid Mosaic Model

• The plasma membrane is fluid, with proteins floating within a phospholipid bilayer.
• Membrane proteins vary in size and function, maintaining a dynamic cellular environment.

 

 

In a nutshell

• Phospholipid Bilayer = Selective Barrier.
• Membrane Proteins = Transport & Signaling.
• Na⁺/K⁺ Pump = Energy-Driven Ion Exchange.