1. Membrane Structure & Function
Chapter 7
Membrane Structure & Function

3. Membrane Structure, I Shows Selective permeability
Known as the plasma membrane
Amphipathic - hydrophobic & hydrophilic regions
Singer-Nicolson developed the fluid mosaic model

5. Membrane Structure, II “Mosaic” Structure due to:
Phospholipids - membrane fluidity
Cholesterol - membrane stabilization
“Mosaic” Structure due to:
Integral proteins - transmembrane proteins
Peripheral proteins - surface of membrane
Membrane carbohydrates -~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

7. Membrane Structure, III
Membrane protein functions:
Transport
Enzymatic activity
Signal transduction
Intercellular joining
Cell-cell recognition
ECM attachment

9. Membrane Traffic
Diffusion - tendency of any molecule to spread out into available space
Concentration gradient – moves from high to low
Passive transport - diffusion of a substance across a biological membrane
Osmosis - the diffusion of water across a selectively permeable membrane; DOWN the concentration gradient

11. Water Balance Osmoregulation - control of water balance
Hypertonic - higher concentration of solutes
Hypotonic - lower concentration of solutes
Isotonic - equal concentrations of solutes

12. Water Balance Cells with Walls (plants, bacteria):
Require hypotonic external environments to keep their turgor pressure (water pressure pushing cell membrane out against cell wall)
Become limp or flaccid when lose turgor pressure
Plasmolysis - plasma membrane pulls away from cell wall

13. Water Balance Cells without Walls (animals, most protist):
Require isotonic external environments
Hypertonic environments – cells swell & may burst with too much water pressure (Cytolysis)
May have contractile vacuoles (some protists) to control internal water pressure

15. Specialized Transport
Transport proteins (with or without channels)
Facilitated diffusion - passage of molecules and ions with transport proteins across a membrane down the concentration gradient
Active transport - movement of a substance against its concentration gradient with the help of cellular energy

17. Types of Active Transport
Sodium-potassium pump
Exocytosis - secretion of macromolecules by the fusion of vesicles with the plasma membrane
Endocytosis - import of macromolecules by forming new vesicles with the plasma membrane
Phagocytosis –cell “eating”
Pinocytosis – cell “drinking”
Receptor-mediated endocytosis (ligands)