Biological Membranes

1. Biological Membranes

2. Biological membranes • Complex, dynamic structures made of lipid and protein molecules • Perform many functions • Define cell as a compartment • Regulate passage of materials • Participate in chemical reactions • Transmit signals between cell interior and the environment • Act as part of energy transfer and storage

3. Biological membranes • Physically separate cell interior from extracellular environment • Form compartments within eukaryotic cells • Plasma membrane • Regulates passage of materials • Participates in biochemical reactions • Receives information about environment • Communicates with other cells

4. Phospholipids form bilayers in water Phospholipids in water Detergent in water

5. Fluid mosaic model • Membranes consist of fluid phospholipid bilayer with a mosaic pattern of associated proteins • Phospholipid molecules are amphipathic and contain • Hydrophobic regions • Hydrophilic regions

6. Plasma membrane of mammalian red blood cell

7. Membrane properties • Orderly arrangement of phospholipid molecules make the cell membrane a liquid crystal • Allow molecules to move rapidly • Proteins move within membrane • Lipid bilayers are • Flexible • Self-sealing • Can fuse with other membranes

8. Detailed structure of the plasma membrane

9. Integral membrane proteins • Embedded in the bilayer • Transmembrane proteins • Integral proteins that extend completely through the membrane • Peripheral member proteins • Associated with the surface of the bilayer

10. Membrane proteins, lipids, and carbohydrates • Asymmetrically positioned to bilayer • Sides have different composition and structure • Function of member proteins • Transport of materials • Acting as enzymes or receptors • Cell recognition • Structurally linking cells

11. Asymmetry of the plasma membrane

12. Functions of membrane proteins

13. Membranes are selectively permeable • Physical processes • Osmosis • Diffusion • Carrier-mediated processes • Channel proteins • Carrier proteins

14. Diffusion: net movement of a substance from a region of greater to lower concentration

15. Osmosis: water passes throughselectively permeable membranefrom region of higherconcentrationto lower

16. Osmotic pressure • Concentration of dissolved substances in a solution • Isotonic: equal solute concentration • Hypertonic: loses water in plasmolysis • Hypotonic: gains water and swells • Turgor pressure • Internal hydrostatic pressure in walled cells

17. Responseof animalcells to osmotic pressure

18. Turgor pressure and plasmolysis

19. Facilitated diffusion • Occurs down a concentration gradient • Active transport • Moves ions or molecules against a concentration gradient • Cotransport • ATP-powered pump maintains a concentration gradient

20. Sodium-potassiumpump

21. Cells expend metabolic energy to carry on physiological processes • Exocytosis • Endocytosis • Phagocytosis • Pinocytosis • Receptor-mediated endocytosis

22. Exocytosis

23. Phagocytosis

24. Pinocytosis

25. Receptor-mediated endocytosis

26. Cells communicate by cell signaling • Signaling molecules include • Neurotransmitters • Hormones • Regulatory molecules

27. Cell signaling involves • Synthesis and release of signaling molecule • Transport to target cells • Reception by target cells • Signal transduction • Response by the cell • Termination of signal

28. Signaltransduction

29. Cells in close contact often develop intercellular junctions • Anchoring junctions • Desmosomes • Adhering junctions • Tight junctions • Gap junctions • Plasmodesmata

30. Desmosomes

31. Tight junctions

32. Gap junctions

33. Plasmodesmata