Molecular Biology of the Cell

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Unformatted text preview: Click to edit Master subtitle style MEMBRANE TRANSPORT Confusing Thought Question of the week In one of my wife's nursing classes she learned that on 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 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?) Concentration and Charge Differences Affect Movement of Molecules Fig 11-4, 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 Fig 11-1, MBOC5 Passive Transport-General Passive transport --- includes simple diffusion (+ osmosis) and facilitated diffusion Characteristics in common energy source – concentration difference between the outside & inside of the cell l free energy released in diffusion. – 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 Fig 11-4, (FACILITATED DIFFUSION) Simple diffusion/Passive – no protein required Small, uncharged molecules Small, polar molecules Rate of Transport by Carrier Protein Fig 11-7, What is going on ? Explain why the data for facilitated diffusion differ from that of simple diffusion Facilitated Diffusion – General transmembrane protein is a transporter but does not uses ATP Carriers or Channels - specific closely related molecule – Ex: glucose transporter will also carry mannose, galactose – BUT only D-isomers, not L-isomers bidirectional faster than simple diffusion Facilitated diffusion 1. Carrier Proteins binding of substance causes conformational change, shifting the "opening" to the other side. this shift also lessons affinity of transporter to substance and substance released. Interesting side note: Glucose transporter Glucose moves into the liver – Carrier proteins How does a liver cell keep from reaching the saturation point. What keeps glucose from moving back? Glucose transporter mechanism used to keep the concentration of glucose lower on the inside of the cell than on the outside: Cell converts glucose --> G-6-P (“glucose - 6 - phosphate”) G-6-P cannot pass through the transporter. Facilitated Transport 2. Ion Channel Proteins Selectivity...
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This note was uploaded on 04/20/2010 for the course BIOL 4064 taught by Professor Dr.reyna during the Spring '09 term at Ouachita Baptist.

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