1. Cell Ultrastructure Membranes

2. Plasma membrane zOutermost layer of cytoplasm zServes as a barrier to prevent cell contains from mixing with the surroundings zAllows molecules to enter and leave zContains protein sensors that allow cell to interact with environment zAllows cell growth and movement zMany other functions as well

3. Some Membrane Functions

4. Membrane Distribution zProkaryotes have a single membrane - the plasma membrane zEukaryotes yPlasma membrane yMany internal membranes that enclose organelles

5. Prokaryotes and Eukaryotes

6. Membranes in a Eukaryotic Cell

7. Membrane composition z1890s - thought membranes largely lipid z1930s - membranes determined to be lipid AND protein zVarious models developed over the years zToday biologists accept the fluid mosaic model of membrane structure ylipid bilayer with scattered proteins

8. Fluid Mosaic Model

9. Membrane Lipids

10. Phospholipids

11. Lipid Bilayer

12. In water a phospholipid bilayer will form a closed spherical vesicle

13. Lipid Bilayer is Fluid z Lipid molecules in each monolayer can yrotate ymove laterally - change position with neighbor z Fluidity due to unsaturated FA chains and cholesterol z Flip-flop does not occur

14. Cholesterol

15. Cholesterol and unsaturated FA prevent packing of phospholipids

16. Components of Model

17. Protein Properties

18. Integral Proteins zIntegral Proteins have a hydrophobic region zNonpolar side chains immersed in lipid bilayer

19. Various Protein Shapes

20. Examples of Plasma Membrane Proteins and Their Functions

21. Membrane Proteins

23. Glycocalyx

24. Membrane Asymmetry

25. Cell fusion experiment proves membrane is fluid

26. Membranes Are Selective Barriers zMembranes have a variety of functions but the most basic function is that of a permeability barrier zMembranes serve as selective barriers that regulate the passage of materials into and out of cells (or organelles) zAny substance that enters or leaves a cell must pass through the membrane

27. Membrane Barriers zFor a material to cross a membrane yThe membrane must be permeable to that substance yOR the material is transported across the membrane

28. Membrane Permeability zIf a membrane is permeable to a substance that means that the substance is able to diffuse across or through the membrane

29. Kinetic Energy zAll particles (all matter in the universe) possess a certain amount of kinetic energy - results in random motion of particles (Brownian Movement) zLargely as a result of temperature (temp is a measure of average kinetic energy) zBecause particles are in constant motion, there are several effects - diffusion is one

30. Diffusion zNet movement of particles from a region of higher concentration of the substance to a region of lower concentration zNet movement because there is always some in all directions because of the random movement zParticles of a substance tend to become distributed within the available space

31. Diffusion zDiffusion is fastest in gases ySlower in liquids yInfinitely slow in solids zNet effect is always from a region of high concentration to lower concentration as long as temperature and pressure are equal yOr from a region of high free energy to lower free energy

32. Diffusion

33. Diffusion and Osmosis ABA B Membrane is permeable to water but not to glucose molecules Osmosis is the diffusion of water across a differentially permeable membrane

34. Measuring Osmotic Pressure

35. Osmosis in Animal Cells Area outside cell is Hypotonic or Hypo-osmotic

36. Osmosis in Animal Cells Equal concentrations of solutes inside and outside Isotonic or Iso-osmotic concentrations Concentration of solutes lower inside the cell - water will leave Area outside is hypertonic or hyperosmotic - Plasmolyzed

37. Plant Cells Iso-osmotic Hypo-osmotic Hyperosmotic