2. Cell Membrane Thin layer of lipid and proteins Separates the cell’s contents from the environment Phospholipid bilayer Two layers of lipid (made from glycerol), two fatty acids, and a phosphate group. Head - hydrophilic Tail – hydrophobic Cell membranes are fluid

4.  Membranes are held by hydrophobic interactions  Lipids can move laterally › Very rapid  Proteins move much slower

5.  Temperature affects fluidity › Decrease – phospholipids will settle into closely packed arrangements and solidify › Dependent on type of lipid  Unsaturated hydrocarbon tails – lower temperature tolerance › Other molecular affects  Cholesterol – actually solidifies animal membranes

6.  Determine the majority of membrane functions › Integral proteins › Peripheral proteins

7.  Transport  Enzymatic activity  Signal transduction  Cell to cell recognition  Intercellular joining  Attachment to the cytoskeleton/ECM

8.  Non-polar molecules dissolve through membrane  Transport proteins › Needed for polar molecules › Aquaporins – water › Proteins are specific to the molecule they move

9. › Diffusion Process in which molecules move from an area of high concentration to an area of low concentration Equilibrium  When the concentration of the solute is the same throughout the solution

10. Diffusion through cell boundaries › Measuring Concentration Cytoplasm is a solution mainly of water Concentration  The mass of solute in a given volume of solution  Mass/volume (g/L)

11. Osmosis › The diffusion of water through a selectively permeable membrane

12. › How does it work? Isotonic  Solutions are the same strength Hypertonic  One solution is above strength Hypotonic  One solution is below strength

13. › Osmotic Pressure The minimum amount of pressure needed to stop the flow of water across the membrane Used by the kidneys to move water in and out of tubules during filtration

14. Facilitated diffusion › A protein channel that helps a specific molecule to diffuse into a cell

15. Active transport › Moving molecules against a concentration difference › Molecular transport Requires energy to move small molecules or ions across the membrane

16.  Sodium-Potassium Pump › ATP transfers phosphate to transport protein › Shape changes › 3 Na for 2 K  Resting membrane potential

17.  Cotransport › Substances pumped out can do work › Diffusion of the substance back across the membrane  Hydrogen pump

18. › Endocytosis Taking material into the cell by means of infolding Phagocytosis  Cell eating Pinocytosis  Taking in liquid by endocytosis › Exocytosis Releasing material from the cell by the opposite process of endocytosis