Cell Membrane & Transport  Fluid mosaic model - Lipids, proteins & carbohydrates  Membrane trafficking - Passive Transport - Active Transport - Bulk Transport

Plasma Membrane - Phospholipid Bilayer  Composition: - lipids, proteins & carbohydrates  Phospholipids, cholesterol & glycolipids - head: contains a polar phosphate group (hydrophilic) - tails: 2 nonpolar hydrocarbon fatty acid (hydrophobic)  Functions : - protection - controls traffic - selective permeable - anchoring/fusion

Fluid-Mosaic Model of Plasma Membrane

Functions of Membrane Proteins

Membrane Trafficking

Passive Transport  Simple diffusion: mov’t of molecules from a region of high  [ ]  low   Concentration gradient: difference in [ ] b/t two regions - substances always move in the direction of the [ ] gradient  Membrane permeability of lipid bilayer - nonpolar vs polar molecules

O2 & CO2 can cross a lipid bilayer without help from membrane proteins – what properties allow this to occur?

Diffusion Properties  Characteristics: not carrier-mediated,  [ ] gradient & passive  Definitions: solution, solvent & solutes  Factors that influence rate of diffusion: –temperature –state of solvent –size of molecules –diffusion gradient –membrane structure So what is solubility?

Osmosis  Diffusion of H 2 O across a selectively permeable membrane from a region of  solute [ ] to a  solute [ ]  establish equilibrium  Osmotic pressure: pressure applied to the cell membrane from flow of H 2 O during osmosis -- # of particles in solution  Tonicity: the ability of a solution to cause a cell to gain or lose water - isotonic, hypotonic & hypertonic

Facilitated Diffusion: Passive Transport Aided by Proteins Carrier proteins

 Primary active transport: movement of solutes against [ ] gradient  biological membrane - energy dependent  Na + /K + -ATPase pump: –resting membrane potential –osmotic balance –drives other pumps  Electrogenic pump Active Transport ATP