BIOL 2242 Lecture Notes - Lecture 8: Membrane Transport Protein, Alpha Helix, Facilitated Diffusion
5 Feb 2018
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As 1 or more helices: transport +/or enzymatic functions. Peripheral/extrinsic: attached to 1 side of membrane only. 4. 10, p. 83: 1 alpha helix, multiple helices, central bits are hydrophobic (as is inner portion of membrane) Recall: transport across membranes (fig 4. 11, p. 83: non-polar substances and gases cross freely via simple diffusion. Along gradient, little subject to cell control: h20, though polar, also passes freely. Facilitated by aquaporins (h2o transport proteins: polar substances (including small ions) are blocked at membrane. Small ions have hydration shell that increases their size. Must use transport proteins (passive or active), subject to cell control. Determined by concentration & charge (if ion: no energy input. But cell uses nrg to maintain negative charge to promote cation uptake: 2 modes. In form of atp vian ion pumps: 2 types. Primary active transport: moves substance directly e. g. h+atpase. Secondary active transport: moves substances against its ec gradient by linking to ion pump e. g. h+-sucrose.
