2. AP Biology The Cell Membrane *Very thin (7.5-10 nm) *Elastic *Semipermeable * Dynamic *lipid bilayer *Made of phospholipids, proteins, CHO& otherlipids *amphipathic

3. AP Biology Phospholipids Fatty acid Phosphate Flexibility & selective permeability  Fatty acid tails  hydrophobic  Phosphate group head  hydrophilic  Arranged as a bilayer

4. AP Biology Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

5. AP Biology  Protein: *Hydrophilic & hydrophobic *Integral & peripheral  Cholesterol: permeability & toughness  CHO: recognition sites & attach cells together Glycoprotein Glycolipid Peripheral protein Cholesterol

6. AP Biology Functions of membrane proteins  1- structural ptns  2- passive channels: ungated & gated(voltage / ligand)  3- carriers for facilitated diffusion  4- carriers for active transport (uniport /symport/ antiport)  5- receptors: number & sensitivity change  6- enzymes  7- identity ptns  8-intercellular connections: a. binding j: tight & desmosomes b. gap j  9- cell adhesion molecules  10- fixation of cytoskeleton

7. AP Biology Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion

8. AP Biology Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish one cell from another  antigens  important in organ & tissue development  basis for rejection of foreign cells by immune system

9. AP Biology 2007-2008 Movement across the Cell Membrane

10. AP Biology Diffusion  All molecules are in constant motion  Diffusion  movement from high  low concentration  Diffusion  movement from high  low concentration

11. AP Biology

12. Facilitated Diffusion  Diffusion through protein channels  channels move specific molecules across cell membrane  no energy needed open channel = fast transport facilitated = with help high low

13. AP Biology Facilitated Diffusion

14. AP Biology Active Transport “The Doorman” conformational change  Against concentration gradient  Needs carrier protein  Energy is needed ATP low high

15. AP Biology symportantiport Active transport  Many models & mechanisms ATP

16. AP Biology Active transport  1ry active: * eg Na+/K+ pump *α &β subunits *α subunit contains 2 binding sites for K+ on the outside & 3 binding sites for Na+ on the inside & an ATP binding site *β subunit has ATPase activity.  2ry active: * eg Glucose transport 2ry to active transport of Na 1 st Na pumped out ….creates concentration gradient… Na & glucose bind a carrier…transports them to inside

17. AP Biology Getting through cell membrane  Passive Transport  Simple diffusion  diffusion of nonpolar, hydrophobic molecules  lipids  high  low concentration gradient  Facilitated transport  diffusion of polar, hydrophilic molecules  through a protein channel  high  low concentration gradient  Active transport  diffusion against concentration gradient  low  high  uses a protein pump  requires ATP  Vesicular transport ATP

18. AP Biology Transport summary simple diffusion facilitated diffusion active transport ATP

19. AP Biology How about large molecules?  Moving large molecules into & out of cell  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating”  pinocytosis = “cellular drinking”  exocytosis exocytosis

20. AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

21. AP Biology Osmosis is diffusion of water  Diffusion of water from high concentration of water to low concentration of water  across a semi-permeable membrane  The pressure necessary to stop solvent mol movements= osmotic pressure  The numbers of particles per unit volume of fluid  Measured in mmHg  Osmole osmolarity osmolality

22. AP Biology  The osmolarity of ICF=that ECF=300 mosmol  280 mosmol is due to Na, Cl & HCO3  20 mosmol is due to protein  Tonicity: is the osmolality of a solution relative to the plasma  Plasma proteins of blood is called oncotic pressure. It is important for capillary circulation &regulation of ECF

23. AP Biology Concentration of water  Direction of osmosis is determined by comparing total solute concentrations  Hypertonic - more solute, less water  Hypotonic - less solute, more water  Isotonic - equal solute, equal water hypotonichypertonic water net movement of water

24. AP Biology Donnan effect  The protein anions inside the cells are non diffusible hinder the diffusion of diffusible cations  More osmotically active particles inside the cell  The cell tends to swell  But the Na+/ K+ pump prevents cell rupture

25. AP Biology Any Questions??