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36 Cards in this Set
- Front
- Back
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What kinds of molecules CAN go through a membrane w/out a transporter?
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Hydrophobic (drugs, carcinogens; small uncharged polar (water, urea, glycerol)
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What kinds of molecules canNOT go through a membrane w/out a transporter?
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Large uncharged polar molecules (like sugars and nucleosides); charged molecules like amino acids and nucleotides
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What is membrane transport?
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The movement of molecules across cell membranes.
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What are the two classes of membrane transport?
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Protein-mediated; simple membrane diffusion
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What are characteristics of protein-mediate transport
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Rapid, stereoselective, and saturable. @ a certain pt, you can't get any more through
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What are the characteristics of simple diffusion:
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Nonspecific and very slow (relatively); use for h-phobic and nonpolar
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What are the two main classes of membrane transport proteins?
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Transporters and channels
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How do transporters work? What are they?
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They are pumps that pump molecules against the electrochemical gradient. They are enzymes.
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What's a passive transporter?
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An enzyme that accelerates the rate @ which a molecule achieves equilibrium across the cell membrane, providing an alternative rxn pathway.
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What's an active transporter?
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SOME use ATP to create rapid solute movement against a concentration gradient (upill). OTHERS use Na+ and K+ gradients to drive a molecule against its chem gradient.
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As with other enzymes, membrane transporters display saturation _____ and _____ or ______ inhibition.
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kinetics; competitive; noncompetitive
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What's the major difference between passive and active transport?
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Passive: substrate diffuses down chemical gradient; nondirectional. Active: substrate goes up its chemical gradient using energy; directional
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What are the two types of passive transporters?
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Uniport and antiport.
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Describe a uniport transporter.
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Passes only 1 molecule. Simple carrier. Goes from high [s] to low [s].
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Describe an antiport transporter.
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Exchange only carrier. Exchanges one molecule for another. If you had high [Na+] in and high [Ca2+] out, you need both to bind, undergo conformational change, and then exchange one for the other.
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What are the characteristics of simple diffusion:
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Nonspecific and very slow (relatively); use for h-phobic and nonpolar
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What are the two main classes of membrane transport proteins?
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Transporters and channels
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How do transporters work? What are they?
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They are pumps that pump molecules against the electrochemical gradient. They are enzymes.
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What's a passive transporter? What's a classic example?
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An enzyme that accelerates the rate @ which a molecule achieves equilibrium across the cell membrane, providing an alternative rxn pathway. Example: the GluT1 Glucose transporter (must have D-glucose).
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What's an active transporter?
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SOME use ATP to create rapid solute movement against a concentration gradient (upill). OTHERS use Na+ and K+ gradients to drive a molecule against its chem gradient.
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How does a passive transporter work?
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The transporter is in open confirmation. It binds. It closes and let the molecule fall into the cell. Its either open OR closed. Never both @ the same time.
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What is Cytochalasin B?
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An inhibitor of glucose transport. It acts @ the cytoplasmic surface of the sugar transporter (inside cell). It's a competivie inhibitor of sugar and fights for that binding site. Doesn't matter what's going on outside, b/c it's on cytoplasmic side
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What role does Maltose play?
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It also inhibits sugar by binding to an extracellular site on the transporter. It's a competitive inhibitor also. Only affects the outward binding (b/c it's on the outside). It's a competitive inhibitor of cytochalasin B.
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The carrier mechanism--what do cytochalasin B and maltose show us?
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That in the absense of substrate the transporter can exist in one of two forms, E1 or E2, which will present a binding site to either inside or outside of cell.
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How does Prozac work as an inhibitor?
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Prozac inhibits the serotonin reuptake transporter, a membrane protein which reuptakes serotonin into the cell @ synapse after it's been released. By blocking this, serotonin stays in synaptic cleft longer.
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What are the 3 kinds of active transporters?
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Symport. Uniport. Antiport.
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Describe symport.
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Co-transprot. Use Na/K gradients to drive a substrate against its chemical gradient. Everything goes in one direction. One is driving force, and other drags ion against its chem gradient. Examples are neurotransmitter transport in synaptic cleft and sugar and a.a. transport in epithlia.
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Describe uniport, ATPase.
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Use ATP from inside cells to pump stuff outside.
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Antiport (ATPase).
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1/3 of ATP is burned by this pump. Na outside and K inside for every ATP hydrolysis
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What does furosemide do?
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It blocks the Na+, K+, and 2Cl- symporter in the nephron and the loop of Henle. You get more salt and water excretion (diuretic), and blood pressure goes down, along with blood volume.
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Why does blocking the symporter do this?
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B/c we're blocking a symporter that lets you use the Na+ gradient to pull Na+ and water out of the loop. Now it just goes to collecting duct.
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Na+/K+ ATPase. Some details.
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1/3 of a cells ATP is used for this pump. Goes 100times/sec. We transfer 3Na+ outside and 2K+ inside (against gradient); closely coupled to ATP hydrolysis. It sets the gradient in all our cells.
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What does digoxin do?
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Increase force of contraction of heart muscle.
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How does it work?
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It inhibits the Na+/K+ ATPase and the Na+ gradient transmembrane is diminished.
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What happens if we have a weaker Na+ gradient?
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It affects other exchangers. The Na+/Ca2+ antiporter. We get less Ca2+ efflux to extracell space. This raises SR Ca2+ levels and makes heart beat harder and harder.
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Biggest concern if we bind to the pump?
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We keep diminishing our Na+ gradient. heart beats harder and harder, and cell can't maintain gradient, blows up and dies.
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