Cell Membrane

Cell Membrane

1. Plasma membrane

   • Phospholipid bilayer
   • Allows for compartmentalization within cell
   • In cell surface or around organelles
   • Fluid mosaic model
     • Protein and lipid components moving rapidly and laterally in plane of membrane
     • Protein molecules randomly scattered and floating in bilayer
     • Hydrophilic regions exposed to water
     • Asymmetrical; differ in composition

2. Phospholipids

   • Amphipathic
     • Hydrophilic phosphate heads
     • Hydrophobic hydrocarbon tails
       • Saturated
       • Unsaturated
         • C=C bonds causing kink
         • Disrupts close and orderly packing making membrane more fluid
   • From fluid matrix due to weak hydrophobic interactions between fatty acid chains

3. Cholesterol

   • Amphipathic
   • OH group aligns with phospholipid head
   • Bulky steroid and hydrocarbon chain tucked between fatty acid chains
   • Interferes with tight packing of hydrocarbon chains in lipid bilayer
   • Functions
     • Low/High temeperature
       • Increase bilayer fluidity preventing freezing
       • Decreases bilayer fluidity preventing melting
     • Mortar
       • Improves membrane impermeability

4. Proteins

   • Determine membrane's specific function
   • Randomly arranged and floating in phospholipid bilayer
   • Unique collection within and on different cells
   • Distribution
     • Integral
     • Peripheral
   • Function
     • Active site
     • Facilitated diffusion and osmosis
     • Enzymes
     • Receptor sites

5. Carbohydrates

   • Short branched chain of sugars
   • Kept in contact with external aqueous environment (hydrophilic)
   • Exist as
     • Glycoproteins
     • Glycolipids
   • Functions
     • Cell-cell recognition
     • Cell-cell adhesion

6. Functions

   • Boundary between cell and environment
   • Compartmentalization within cell
   • Regulation of transport
   • Detection and transmission of signals
   • Cell-cell communication
   • Attachment to membrane bound enzymes