UA BIOC 460 - Biological Membranes (11 pages)

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Biological Membranes



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Biological Membranes

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Pages:
11
School:
University of Arizona
Course:
Bioc 460 - Proteins and Metabolism
Proteins and Metabolism Documents

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LEC20 21 MembraneTransport 02 27 2007 05 16 PM Lectures 20 21 Biological Membranes 3 4 Transport PDF Reading Berg Tymoczko Stryer Chapter 13 pp 345 364 problems in textbook chapter 13 pp 379 380 1 3 done in lecture notes 14a 20 Updated on 2 27 07 at 4 15 pm Key Concepts Free energy of transporting material across membrane depends on concentration gradient across membrane For uncharged solutes Solutes move spontaneously G t 0 from compartment of higher concentration to compartment of lower concentration Equilibrium G 0 when C1 C2 Charged solutes presence of a membrane potential as well as the chemical concentration gradient influences the distribution of ions Passive transport spontaneous passage of solute down its concentration and or electrical potential gradient no input of free energy required Simple diffusion no assistance Facilitated diffusion rate enhanced by carrier or channel generally an integral membrane protein transporter or permease rapid diffusion down a concentration gradient saturable reaches a maximum velocity that depends on transporter concentration specific depends on interaction of solute with transporter Example GLUT1 glucose transporter in erythrocytes Gated ion channels ligand gated or voltage gated VERY rapid 107 108 ions sec down a concentration gradient not saturable degree of specificity ion selectivity varies Examples Acetylcholine receptor of motor neurons bacterial potassium channel Eukaryotic sodium potassium and calcium channels Uniport system in which one solute transported Cotransport system in which transport of one solute is coupled to transport of another Symport different solutes transported in same direction Antiport different solutes transported in opposite directions Active transport Primary active transport transport of solute against its concentration gradient coupled directly to an exergonic chemical reaction e g ATP hydrolysis Examples Ca 2 ATPase of muscle cell sarcoplasmic reticulum Na K ATPase of animal cell plasma



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