1. Plasma membrane Structure Read p.115-117

2. Is there a plasma membrane? People were skeptical that the plasma membrane existed (too thin to see) The theory was formulated purely by circumstantial evidence by the information of what passes in and out of the cell (lipid soluble material = dissolves in fats) A test for lipids concluded that it did exist

3. Visual Evidence 1950’s brought visual evidence with the invention of better microscopes –Observed 2 dark lines separated by a clear line –Suggested a 2- layer structure

4. Plasma membrane Very thin…8000 membranes = the thickness of 1 page of paper!! Serves as boundaries around organelles and the cell itself Made of 2 layers of phospholipids

5. Phospholipid Bilayer Heads Tails Heads

6. Structure of phospholipid Head –Hydrophilic (“water-loving”) –Polar (easily attracted to charged particles) –Water soluble, which allows the membrane to act like a fluid Head

7. Structure of phospholipid Tails (2 tails) –Hydrophobic (“water-hating”) –Flexibility varies –Non-polar (not attracted to charged particles) Tails

8. Phospholipid Bilayer

9. Structure of the membrane Phospholipids lay tail to tail creating a phospholipid bilayer The bilayer is arranged so that the heads point outward towards the cytoplasm or the watery environment cells live in (both are polar)

10. Membrane proteins are found throughout the plasma membrane to perform different jobs – enzyme activity – cell to cell recognition – cell signaling – exchanging material

11. Membrane Proteins p. 117

12. Heads Tails