CHEM 271 Chapter 13: chem 271 chapter 13
3 May 2016
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Chem 271 chapter 13 membrane channels and pumps. Permeability is conferred by three classes of membrane proteins: pumps, carriers, and channels. Pumps use a source of free energy such as atp hydrolysis or light absorption to drive the thermodynamically uphill transport of ions or molecules. Carriers mediate the transport of ions and small molecules across the membrane without consumption of atp. Channels provide a membrane pore through which ions can flow very rapidly in a thermodynamically downhill direction passive transport / facilitated diffusion. Pumps are energy transducers, they convert one form of free energy into another. Two types of atp-driven pumps, p-type atpases and the atp-binding cassette (abc) transporters, undergo conformational changes on atp binding and hydrolysis that cause a bound ion to be transported across the membrane. Movement across their concentration gradient primary active transport. Carriers utilize the gradient of one ion to drive the transport of another against its gradient secondary active transport.
