Molecular Biology of the Cell

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Unformatted text preview: MEMBRANE TRANSPORT MEMBRANE Confusing Thought Question of the week the In one of my wife's nursing classes she learned that on In treatment for Hyperkalemia (to high [K ] in blood/extracellular fluid) was and IV of glucose and insulin. The teacher said when this was given K just follows the glucose through the membrane. – – – A. what is wrong with this last statement. B why is hyperkalemia bad? C. Suggest a reason why this mechanism works. Transport needs to be unique for every cell and organelle within a organelle cell cell 1. In simple diffusion and facilitated diffusion, molecules move from an area of high concentration (outside the cell) to an area of low concentration (inside the cell). It is implied there is greater energy outside of the cell. Why is there greater energy outside the cell? (Or: why is there greater energy when there is a greater concentration?) there Concentration and Charge Differences Affect Movement of Molecules Affect Fig 11-4, MBOC4 Rank the following substances from the most soluble (permeable) in a phospholipid bilayer to the least soluble (impermeable). O2, CO2, Na+, water, ethanol (CH3CH2OH), urea (H2NCONH2), glycerol (CH2OHCHOHCH2OH), 18-C fatty acid Relative Permeability of Synthetic Lipid Bilayer Lipid Fig 11-1, MBOC5 Passive Transport-General Passive Passive transport --- includes simple diffusion Passive simple (+ osmosis) and facilitated diffusion facilitated Characteristics in common energy source – concentration difference between the outside & inside concentration of the cell of free energy released in diffusion. free – – – direction of transport: with concentration gradient No energy expended by the cell (in form of ATP) Transport protein used in facilitated diffusion Carrier proteins Channel proteins Passive Transport Passive Simple diffusion/Passive – no protein required Small, uncharged molecules Small, polar molecules (FACILITATED DIFFUSION) Fig 11-4, MBOC4 Rate of Transport by Carrier Protein Protein What is going on ? Explain why the data for facilitated diffusion differ from that of simple diffusion Fig 11-7, MBOC4 Facilitated Diffusion – General transmembrane protein is a transporter but does not uses ATP not Carriers or Channels - specific closely related Carriers specific molecule molecule – Ex: glucose transporter will also carry mannose, Ex: galactose galactose – BUT only D-isomers, not L-isomers bidirectional faster than simple diffusion Facilitated diffusion Facilitated 1. Carrier Proteins binding of substance causes conformational binding change, shifting the "opening" to the other side. this shift also lessons affinity of transporter to substance and substance released. Interesting side note: Interesting Glucose transporter Glucose moves into the liver – Carrier Glucose proteins proteins How does a liver cell keep from reaching How the saturation point. the What keeps glucose from moving back? Glucose transporter Glucose mechanism used to keep the mechanism concentration of glucose lower on the inside of the cell than on the outside: the Cell converts glucose --> G-6-P Cell (“glucose - 6 - phosphate”) (“glucose G-6-P cannot pass through the G-6-P transporter. transporter. Selectivity Facilitated Transport Facilitated 2. Ion Channel Proteins – Plasma membranes of plant, animal cells Cell can control opening and closing of Cell channels but movement is with concentration gradient – no direct contact with substrate contact Fig 11-20, MBOC4 (Ion) Channel Proteins (Ion) Can be opened or closed to prevent transport Carrier Proteins vs. Channel Proteins Carrier What are the differences and similarities between the two Fig 11-3, MBOC4 Recently, researchers found that when E. coli cells are exposed to a hypertonic coli (high solute) solution, the bacteria produce a permease that can actively transport K+ into the cell. Of what value is transport into the active transport of K+, which requires the which ATP? ATP? Active transport – General Characteristics General direct or secondary direct secondary direction of transport -- against direction against concentration gradient or electrical potential gradient gradient – unidirectional requires energy (= ATP or light) and is and sensitive to metabolic poisons sensitive requires transmembrane protein requires can be saturated (i.e. there is a max rate) can carriers are specific -- carry single or carriers closely related molecule closely Ways Of Driving Active Transport Secondary Active transport Characteristics of both active and passive Fig 11-8, MBOC4 Direct Active Transport Direct use pumps that are directly dependent on use ATP (they hydrolyze ATP to ADP + Pi) (they Different types of “pumps”: Thought Questions Thought The red blood cells (rbcs) in your body maintain internal concentrations of sodium & potassium ions that are significantly differently from those in blood plasma. However, these gradients of ion concentration can be abolished if isolated rbcs are treated in any of the following ways. Explain how the effectiveness of the treatment shows that the movement of Na and K are energy-requiring processes. (a) If isolated rbcs are held for an extended period of time at 37 °C in a medium without an energy source, they will eventually begin to leak K ions outward and Na ions inward. However, the outward movement of Na ions and inward movement of K ions can be restored by the addition of glucose to the medium. Na+ K+-ATPase pump Na – 3 Na+ out, 2 K+ in – result is NET charge across membrane result (High conc. of Na+ outside) (High – animals only (none in prokaryotes, fungi, plants) – Na/K pump is a P-type (phosphate) Model For Na+/K+ Pump Action Model Fig 11-14, MBOC4 Reasons to Maintain Intracellular [Na+] Intracellular Maintain membrane potential Regulate osmotic pressure by controlling Regulate intracellular [Na+] intracellular Na+ concentration gradient used for coupled active transport of other molecules active - side note: three Na+ are pumped out while 2 side K+ are pumped in - what does this do the net charge? charge? H+ pumps (V-type) H+ ATPases- create ATP Use H+ movement to create ATP Sometimes called H+ pumps but that part of a Sometimes larger class of pumps (V-type or vesicle type) larger Na/K pump is a P-type (phosphate) Can be reversed these pump H+ from cytoplasm into space these enclosed by a vesicle membrane enclosed – lowers pH inside vesicle – maintains neutral pH of cytoplasm – examples of materials pumped in V-type examples pumps: sugars, amino acids, ions pumps: Thought Questions Thought Ouabain is a cardiac glycoside that binds with the carrier proteins involved in the sodium-potassium pump and inhibits the protein's function (i.e. the pump stops). Describe what you expect to be the effects of ouabain on the transport of glucose into the cell How would you (a cell) move glucose from point A to point B point Low [Glucose] High [Na] High [Glucose] Low [Na] Low [Glucose] High [Na] Example- Na+ Gradient Can Drive ExampleGlucose Transport Glucose Binding of glucose and Na+ is cooperative cooperative [Na+] higher outside of cell Glucose is more likely to bind Glucose carrier in A state carrier Both glucose and Na+ enter cell more often than leave cell Secondary active transport – Energy for transport Energy provided by Na+ gradient provided – Na+ gradient established by ATP-driven Na+ pump ATP-driven Fig 11-10, MBOC4 Secondary Active Transport Pumps Couples movement of one molecule with another- Coupled or Co - transport Coupled Secondary active transport? Indirectly uses concentration gradient created by active transport active Still relies on simple diffusion. Directly does not require energy Directly Types of Coupled Transport Remember two molecules are moving 1. One is moving with a concentration gradient created by active transport 2. The other is moving against the gradient (high conc.) (low conc.) Facilitated Transport Fig 11-9, MBOC4 Transport of Glucose Across Cells Transport Fig 11-12, MBOC4 Passive vs. Active Transport Passive (FACILITATED DIFFUSION) Fig 11-4, MBOC4 Confusing Thought Question of the week the In one of my wife's nursing classes she learned that on In treatment for Hyperkalemia (to high [K ] in blood/extracellular fluid) was and IV of glucose and insulin. The teacher said when this was given K just follows the glucose through the membrane. – – – A. what is wrong with this last statement. B why is hyperkalemia bad? C. Suggest a reason why this mechanism works. ...
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This note was uploaded on 04/20/2010 for the course BIOL 4064 taught by Professor Dr.reyna during the Fall '09 term at Ouachita Baptist.

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