Structure of a typical eukaryotic plasma membrane Three Classes of Membrane Proteins (1) Integral membrane proteins (or intrinsic proteins or trans-membrane proteins) (2) Peripheral membrane proteins (3) Lipid-anchored membrane proteins Lipid-anchored membrane proteins Membrane Transport Three types of integral membrane protein transport: (1) Channels and pores (2) Passive transporters (3) Active transporters Table 9.3 Characteristics of membrane transport A. Pores and Channels Pores and channels are transmembrane proteins with a central passage for ions and small molecules Solutes of appropriate size, charge, and molecular structure can diffuse down a concentration gradient Process requires no energy Rate may approach diffusion-controlled limit Membrane transport through a pore or channel Central passage allows molecules and ions of certain size, charge and geometry to transverse the membrane B. Passive Transport Passive transport (facilitated diffusion) does not require an energy source Protein binds solutes and transports them down a concentration gradient Types of passive transport systems Uniport - transporter carries only a single type of solute Some transporters carry out cotransport of two solutes, either in the same direction (symport) or in opposite directions (antiport) Kinetics of passive transport Initial rate of transport increases until a maximum is reached (site is saturated) The erythrocyte membrane contains channels that function to exchange anions, such as chloride (Cl - ) and bicarbonate (HCO 3 - ), across the membrane bilayer. From the following data, describe the effect that exogenous sulfate (SO 4 - ) has on (Cl - ) influx in erythroyctes. Types of active transport Primary active transport is powered by a direct source of energy as ATP, light or electron transport Secondary active transport is driven by an ion concentration gradient Primary active transport protein function Protein binds specific substrate, conformational change allows molecule or ion to be released on the other side of the membrane Secondary active transport in E. coli Oxidation of S red generates a transmembrane proton gradient Movement of H + down its gradient drives lactose transport (lactose permease) Secondary active transport in animals: Na + -K + ATPase Na + gradient (Na + -K + ATPase) drives glucose transport