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Lecture 4

Lecture 4 - Membrane Transport - January 17.docx

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BIOL 2021
Patricia Lakin- Thomas

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January 17, 2013 Lecture 4: Chapter 11 – Membrane Transport ElectroChemical Gradient  Energy of transport comes from passive and active transport  Passive: o Motion occurs because of the electrochemical gradient – diffusion o Uses the free energy of the gradient, using the inherent energy  Active: o Up a gradient, coupled to an energy source o Uses: ATP, Light, Another ion gradient o This ALSO reduces the free energy of the system Membrane Transport Proteins  Active and passive proteins exist  Classification of membrane proteins: o Channels – always passive  Forms pore, selectivity filter – unlike enzymes o Transporters – passive or active  Have to go through a conformational change, like an Enzyme  Look at posted theme on Moodle  General properties of both o Always multi-pass transmembrane proteins o Some are very specific for certain molecules or ions  A lot like enzymes o Rate of transport will saturate at high concentrations  Like enzymes  Vmax and Km exist for these systems, unlike diffusion o Can be inhibited by small molecule inhibitors, like enzymes Passive Transporter Transport  Random flip flop, allowing to flow via gradient o Reduces the free energy o Not necessarily due to binding of solute o Concentration gradient WILL change Active Transporter Transport  Coupled to another energy source – causes conformational change o Coupled transporter  Coupled to an ion gradient  Types of transporters  Uniport – passive – not coupled to anything (* not coupled *)  Symport – active – motion in the same direction o Lactose Permease  Using the proton gradient in bacteria  Symport of protons and lactose o Na+-Glucose transporter  Symmetric – symport  Glucose and Na+ have to be in the transporter to cause change and send the system across the membrane  Epithelial cells – skin, internal membranes  Want to concentrate glucose inside the cells  Driven by E of sodium gradient  Binding of Na increases affinity of glucose – cooperative binding  Antiport – active – motion in opposite directions  Transcellular transport  How to get glucose from gut to bloodstream  fig 11.11 o Glucose/Na+ symport o Glucose uniporter o Na+/K+ pump to cre
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