Cell Membrane Structure and Functions

Cell Membrane Structure

• Phospholipid bilayer: composed of two layers of phospholipid molecules with their hydrophobic (non-polar) tails facing inward and hydrophilic (polar) heads facing outward
• Thickness: approximately 7-10 nanometers (nm)
• Semipermeable: allows certain molecules to pass through while keeping others out

Cell Membrane Functions

• Regulates what enters and leaves the cell
• Maintains cell shape and provides mechanical support
• Acts as a barrier against external substances
• Plays a role in cell signaling and communication

Cell Membrane Components

• Phospholipids: amphipathic molecules that make up the majority of the bilayer
• Proteins: embedded in the bilayer, facilitate transport, signaling, and cell-cell interactions
• Cholesterol: helps maintain membrane fluidity and structure
• Carbohydrates: attached to proteins and lipids, involved in cell-cell recognition and signaling

Cell Membrane Transport

• Passive transport: movement of molecules from high to low concentration without energy input
  • Diffusion: movement of molecules from high to low concentration
  • Osmosis: movement of water molecules through the membrane
• Active transport: movement of molecules from low to high concentration using energy input
  • Carrier proteins: transport molecules across the membrane
  • Pumping mechanisms: use energy to move molecules against their concentration gradient

Fluid Mosaic Model

• Describes the cell membrane as a dynamic, fluid structure with proteins and lipids able to move laterally
• Supports the idea of a semi-fluid membrane that allows for membrane transport and cellular processes