1. Permeability Of Lipid Bilayer Smaller and more hydrophobic molecules diffuse across membrane more rapidly

2. Membrane Transport Proteins Many types; each transports specific molecule Carrier proteins- bind molecule, conformational change Channel proteins- aqueous pore allows passage

3. Passive Versus Active Transport Driven by concentration or electrochemical gradient Mediated by carriers and channels Passive Active Transport against gradient Requires energy input Mediated only by carriers

4. Types Of Carriers Uniport- single molecule Symport- two molecules in same direction Antiport- two molecules in opposite directions

5. Passive Transport By Carriers Resembles enzyme-substrate reaction Binding affinity reflected by K m V max achieved when binding saturated Binding can be inhibited

6. Mechanisms Of Active Transport Driven by ATP hydrolysis (primary active transport) Driven by coupling to passive transport of a different molecule (secondary active transport)

7. Na + -K + Pump [Na + ] higher on outside; [K + ] higher on inside ATP-driven Na + -K + antiporter

8. Na + influx coupled to active transport across plasma membrane Import of sugars and amino acids by Na + -driven symports Using Na + Gradient To Drive Active Transport

9. Transcellular Transport Transport through epithelial cells Active transport by Na + -driven symporters on apical surface Diffusion via carriers on basolateral surface

10. Regulating pH Na + -H + exchanger: Na + gradient drives H + out of the cell ATP-driven H + pumps: H + into intracellular compartments such as lysosomes

11. Maintaining Low Cytosolic Ca 2+ Levels Ca 2+ ATPase (calcium pump): Ca 2+ out of cell or into intra- cellular compartments Na + -Ca 2+ exchanger: Na + gradient drives Ca 2+ out of the cell

12. Classes of ATP-Driven Pumps

13. P-Type Transport ATPases Includes Na + -K + pump and Ca 2+ ATPase Autophosphorylation and subsequent dephosphorylation transmit conformational changes

14. ABC Transporters ATP binding domains: dimerization from ATP binding, dissociation from ATP hydrolysis ATP binding/hydrolysis transmits conformational changes MDR overexpression causes resistance to cancer chemotherapy drugs

15. Osmosis Diffusion of H 2 0 across membrane; facilitated by aquaporins H 2 0 moves from side of low to high solute concentration Water enters cells in hypotonic and leaves in hypertonic solutions

16. Control Of Cell Osmolarity Charged macromolecules and metabolites attract inorganic ions Osmotic gradient pulls in H 2 0 Opposing osmotic gradient generated by Na + (pumped out) and Cl - in extracellular fluid

17. Ion Channels Passive transport Selective Gated

18. Gating Of Ion Channels

19. Resting Membrane Potential Between -20 mV and -200 mV Small flow of ions has large effect

20. Generating Resting Membrane Potential Depends mostly on K + gradient and K + leak channels K + flows out of cell down its electrochemical gradient Equilibrium condition defines resting membrane potential

21. Cystic Fibrosis Cystic fibrosis transmembrane conductance regulator (CFTR) is chloride channel Critical function in epithelial cells lining airway CFTR  F508 mutant not transported to plasma membrane; retained in ER and degraded