2.4

• Cells have membranes that allow them to establish an internal environment
• • Cell membranes provide a boundary between the interior of the cell and the outside environment
• Cell membranes control the transport of materials in and out of the cell
• Phospholipids are amphipathic meaning they are both a Hydrophobic(Non-polar) and Hydrophilic(Polar)
• • The hydrophilic phosphate head is polar
• The hydrophobic fatty acid tail is non-polar
• Phospholipids spontaneously form a bilayer in an aqueous environment

  • Tails inside the bilayer and Heads are exposed to the aqueous outside and inside environments
• Embedded proteins can be hydrophilic or hydrophobic
• • Embedded proteins are found in the cell membrane
• Peripheral proteins are loosely bound to the surface of the membrane
• Peripheral proteins are hydrophilic with charged and polar side groups which allow them to interact with the hydrophilic region of the phospholipid bilayer
• Integral proteins span the membrane
• Integral Proteins are hydrophilic with charged and polar side groups on the ends when they interact with the hydrophilic ends of the phospholipid cell membrane
• Integral proteins are hydrophobic with non-polar side groups that penetrate hydrophobic interior of the bilayer
• Embedded proteins play various roles in maintaining the internal environment of the cell
• Membrane protein functions

  1. Transport
  2. Cell-to-cell recognition
  3. Enzymatic activity
  4. Signal Transduction
  5. Intercellular joining
  6. Attachment for extracellular matrix or cytoskeleton
• The framework of the cell membranes is described as the Fluid Mosaic Model
• The cell membrane is structured as a mosaic of protein molecules in a fluid bilayer of phospholipids(Fluid Mosaic Model)
• The structure (cell membrane) is not static and is held together primarily by hydrophobic interactions which are weaker than covalent bonds
• Most lipids and some proteins can shift and flow along the surface of the membrane or across the bilayer
• The Fluid Mosaic Model components include Proteins,Steroids, and Carbohydrates(Glycoproteins & Glycolipids)
• • Cholesterol (a type of steroid) is randomly distributed and wedged between the phospholipids in the cell membrane of eukaryotic cells
• • Cholesterol regulate bilayer fluidity under different environmental conditions
• • Diversity and location of the (molecules) carbohydrates and lipids enable them to function as markers
• • Glycoproteins - one or more carbohydrates attached to a membrane protein
• • Glycolipids - lipid with one or more carbohydrate attached