1. Cell Membranes

2. PLO’s B9 - analyse the structure and function of the cell membrane
Identify molecules in the membrane and how they contribute the characteristics of the membrane
Describe hydrophobic and hydrophilic regions

3. CELL MEMBRANE STRUCTURE
Fluid Mosaic Model:
Plasma membrane consists of a phospholipid bilayer with protein molecules embedded in it
Phospholipids give a “fluid” consistency
Proteins form the “mosaic”

6. Phospholipids
Phosphate end is polar and hydrophilic (attracted to water)
Fatty acid chains are non polar and hydrophobic

7. Since the membrane is surrounded by water inside and out, the phospholipids arrange themselves like this:

8. Membrane Proteins Peripheral proteins - on the inner or outer surface
Integral proteins - extend right through
Many of the proteins are free to move around laterally within the membrane

9. Membrane Protein Functions
Channels to allow materials in and out of the cell
Transport proteins that carry specific molecules in and out of the cell

10. Receptors for hormones, growth factors and other chemicals that bind to the outside of the cell
Enzymes to catalyze reactions in the cell

11. Connecting cells to other cells at junctions
Ex. Gap junctions (allow passage of materials from cell to cell), tight junctions (connect cells together)

12. Carbohydrates
Carbohydrate chains are attached to some lipid and protein molecules
(glycolipids & glycoproteins)
Usually attached to the outer surface
These are different in each individual
Cell recognition - “ID cards”, enable the body to recognize its own cells

13. Cholesterol Embedded in the membrane
Helps to maintain the fluidity and flexibility of the membrane
Helps to hold the proteins in place
Reduces permeability of the membrane

14. Membrane Permeability
Cell membranes are differentially (selectively) permeable
Certain substances can move through freely (water, gases, small molecules, uncharged (non-polar) molecules
Others cannot, and require special processes to get through (larger molecules, ions)