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BU BIOL 302 - Membrane Transport pt 2
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BIOL 302 1st Edition Lecture 20Outline of Last Lecture I. Membrane transport pt 1 Outline of Current Lecture I. Membrane transportII. Membrane channelsIII. CarriersIV. pumpsCurrent LectureI. Ligand gated ion channelII. Acetylcholine receptor – a ligand gated ion channelThese 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.III. Acetylcholine receptorA. a ligand gated ion channelIV. Acetylcholine receptorA. a ligand gated ion channelB. Inactivation gate, or “ball and chain”1. Amino-terminal domain acts as a “ball” that quickly gets pulled into the channel to occlude it.2. Deletion of the ball domain results in a channel that is permanently conducting.3. The N-terminal peptide alone is enough to close the channel.V. Black lipid membraneA. measure transport through membranesVI. Protein translocating channelA. opens when signal peptide is added VII. PatchA. Patch-Clamp allows to study single channels (Neher)VIII. Patch-ClampIX. Water channelsA. AquaporinX. Water channelsA. Aquaporin1. Water channels:a. In certain tissues, rapid water transport through membranes is necessary.2. Lens in eyes:a. highly permeable for water3. Kidneya. water must be reabsorbed into the bloodstream after filtrationb. Secretion of saliva and tearsXI. Water channelsA. Constricted region1. ar/R selectivity filter (aromatic/arginine) Strips H-bonds from water2. + charge blocks protons proton gradient stays intactXII. Water channelsA. Green spheres are water molecules B. Side chains and –C=O of backbone of residues lining the channel make hydrogen bonds with water, allowing molecules to break H-bonds with bulk waterC. But other small, polar, uncharged molecules can also make similar H-bondsXIII. Clicker question: What is the amount of energy ∆G required to transport Na+ out of cells when:A. the outside concentration is 143 mM B. inside concentration is 14 mM C. voltage potential is 70mV (more negative inside)D. temperature is 37 °C1. 6 kJ/mol2. -6 kJ/mol3. 13 kJ/mol4. -13 kJ/mol5. 0 kJ/molXIV. Active transportA. Secondary active transporters use the free energy stored in a concentration gradient to transport their substrate against the concentration gradientXV. Secondary active transportersA. lactose permease is a symporter that uses the proton gradient to transport lactose into the cell B. lactose permease illustrates secondary active transport that is dependent on a proton concentration gradientXVI. Secondary active transportersA. lactose permease is a symporter that uses the proton gradient to transport lactose into the cell1. As bacteria carry out electron transport, protons are pumped out to the periplasm2. - Protons from the periplasm bind easily because 3. proton concentration is high in periplasm4. - Protons release easily into the cytoplasm because proton concentration is lower in cytoplasm5. Protons are moving down their concentration gradient6. For lactose, it is opposite. Lactose is being transported up its concentration gradient. Bacteria need to transport it in even if concentration in cytoplasm is high because the lactose is needed as carbon source. 7. Lac permease is an example of a SYMPORT XVII. Structure of lactose permeaseA. in its inward facing state with lactose bound (Ron Kaback, UCLA)XVIII. Secondary active transportersA. lactose permease is a symporter that uses the proton gradient to transport lactose into the cellXIX. ATP-driven pumps use ATP hydrolysis to pump molecules across membranes (primary active transporters)A. ATP drives conformation change B. Note difference in opening to opposite sides of membraneC. Note difference in affinity of solute for membrane proteinXX. P-type ATPasesA. Example: SERCA - a calcium pump B. Ca++ is sequestered in the sarcoplasmic reticulum of muscle when muscle is not contractingC. SERCA works to set up a concentration gradient to be exploited upon contraction XXI. P-type ATPasesA. Calcium ions (green)1. N domain binds ATP2. P domain is phosphorylated3. A links changes in N and P domains to the transmembrane domain, where Calcium is bound.XXII. P-type ATPasesA. Asp 351 phosphorylated by reaction with ATP: note change in conformation, Ca++ will be released XXIII. P-type ATPasesA. Shows the modified amino acid residueB. Phosphate was from ATP C. Anhydride of carboxylic acid and phosphate store energy - Hydrolysis associated with negative GD. Limited lifetime in solutionE. Why is it important that the phosphoanhydride is unstable?XXIV. Non-phosphorylated form binds calciumA. Ca++-bound form binds ATP from cytoplasm, Ca++ trappedB. 3. Asp351 phosphorylatedC. . Ca++ binding site disrupted, Ca++ released to SR, ADP released D. Phosphate hydrolyzed offE. Ca++ binding site of non-phosphorylated form formed, opens to cytoplasmXXV. The phosphorylationA. Asp351 is an energy-requiring reaction made possible only because the phosphate was donated by ATP, which became ADPB. SERCA with phosphate on Asp351 changes shape,affinity for calcium ion decreases, calcium ion released into the interior of the sarcoplasmic reticulum even if the concentration of calcium ions is high inside compared to cytosol.C. When phosphate is hydrolyzed off, SERCA changes conformation back to the original form that bound the calcium ions.D. This illustrates how energy is spent to change the conformation of a carrier, allowing it to bind solute from the side of the membrane with low concentration of the solute and to release it at the side of the membrane with high concentration of the solute.XXVI. P-type ATPasesA. Na+ K+ ATPase is also a P-type ATPase – B. 3 Na+ bind inside the cell when not phosphorylated. When phosphorylated, 3 Na+ are released to outside of cell.C. Also, 2 K+ bind from outside the cell. When phosphate is hydrolyzed off, 2 K+ are released in the cell interiorD. => Membrane potentialXXVII. Clicker question: Is -46.5 kJ/mol from the hydrolysis of 1 mol ATP enough to couple to transport of 3 mol Na+ out of and 2 mol K+ into the cell?A. Yes B. NoXXVIII. P-type ATPasesA. Free energy of hydrolysis of ATP drives membrane transport through protein conformational changes driven by phosphorylation of the transport proteinXXIX. Clicker question: Which of the following does not contribute to the large free energy change of G0 = -30.5 kJ/mol (-7.3 kcal/mol) that is accompanied by ATP hydrolysis to ADP and phoshpate ?A. Reduction of


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BU BIOL 302 - Membrane Transport pt 2

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