F BICH 410 Lecture 25 Outline of Last Lecture Enzyme Regulation Membranes Outline of Current Lecture Transport Membrane o Diffusion of molecule from one side to another o Chemical potential deltaG RTln Ad As o Electric potential charge of ion x faraday s constant 96 465 x membrane potential o Change in free energy Electrochemical potential chemical electrical potential o membrane potential is the potential inside potential outside negative inside negativity greater cytosol inside if analyzing more than one molecule must multiply by total number if ion moves from inside to out then the sign changes but not if moves from outside to inside Transport o Mediated 1 passive mediated facilitated transport or 2 active transport requires energy Facilitated diffusion proteins help to increase rate of transport eventually reaches saturation and can perform uniport symport or antiport o Nonmediated simple diffusion such as water steroids and O2 o Channels transport through pores with high selectivity and can be gated rapid flux through channels Na K Cl K more permeable than N Channels lined with carbonyls which replace water ions around K Na is too small to interact with channel 2 K can be in channel at once o Aquaporins allow high rate of water transport Lined with hydrophobic groups allowing fast transport of water because of repulsion o Carrier transport undergoes structural change pumps or transporters Glut Transporter carrier protein Glut1 4 specific for glucose and Glut5 specific for fructose critical for glucose transport These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o o o Gated Ion Channels gating ligand gated for extracellular ligands ie neurotransmitters or for voltage gated ion channels used in membrane potential Nicotinic acetylcholine receptor Binding of acetylcholine opens allowing Na in at post synaptic clef Nerve impulses high Na outside and K inside neuron stimulation opens channel Na floods in depolarization occurs and K channel opens gate closed preventing equilibrium Active transport energy required ATP light or conc gradient N K ATPase ATP drives Na out and K in Antiport so that three charges exit and two enter all cells spend a lot of ATP maintaining cytosolic Na and K conc Na K ATPase phosphorylation of Asp on transport protein Aspartyl phosphate residue is hydrolyzed when K present Protein is 120 and 35kD Alpha subunit has 10TMD Oubain and digitalis bind to alpha retaining conformation but as Na increases Na Ca atiport is stimulated and Ca increases in sarcoplasmic reticulum increasing muscle contraction because of increased release of Ca Playtoxin binds and keeps transporter open Secondary active transport Ion gradient driven active transport Na K atpase generate electrochemical gradients that can drive endergonic processes Intestinal epithelium cells take up glucose using Na dependent symport o Uptake of glucose is secondary active transport Na gradient maintained by NA K ATPase pump Ca2 ATPase increases cytolic Ca and causes responses such as muscle contraction release of neurotransmitter glycogen breakdown o Ca four times less concentrated in cytosol than extracellular space o Pump is necessary to prevent formation of Ca3 PO4 2 o Large gradient difference maintained using active transport of Ca from Plasma Mem To ER using Ca ATPase pump to keep cytosol Ca levels low H K ATPase gastric mucosa cells secrete HCL at 0 15M o Secretion of H is accomplished by H k atpASE o SECRETED PROTONS COE FROM HYDRATION of CO2 by carbonic anhydrase o Gastric fluid 6pH and cytosol 7 4pH o Histamine binds to cell and activates this pump o Tagamet competes with histamine o Ulcers occur of excess HCL ATP binding cassette ABC transporters o Pump ions sugars AA and can use method of importer or exporter only Eukarya o Cystic fibrosis adrenoleukodystrophy ect are associated with ABC transport defects Cystic fibrosis transmembrane conductance regulator is the only ABC transporter that functions as ion channel CFTR pumps out Cl and Na and water maintains proper fluidity With disease the pumping does not work and thick mucus occurs