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Lectures 3 and 4.docx

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Jane Mitchell

Lectures 3 and 4Lipid bilayer permeable to some molecules o Dependent on hydrophobic tails core of bilayerhydrophobic so hydrophobic molecules easily pass through bilayer because they can interact easily with the tail eg O2 CO2 N2 benzeneAnything with high Hydrophobicity is able to go through bilayer o Small molecules that are uncharged and polar are able to cross but they dont cross that easily eg H2O urea glycerol o Movement of molecules is through simple diffusion through bilayerHigh concentration to low concentration down concentration gradientMore hydrophobic or non polar the molecule the faster it is able to diffuse across the bilayer by simple diffusionLipid bilayer is nonpermeable to some molecules o Dont interact well with hydrophobic tails o Require membrane proteins for transportImportant for cellular processes o EgLarge uncharged polar molecules glucose sucroseIons anything with a chargeMembrane transport proteinsalways multipass Transmembrane proteins to create 3D pore that allows molecules to move through protein and not interact with lipid tails o There is a protein lined path across cell membrane through hydrophobic core created by tails transport polar and charged molecules mainlyEg Ions sugars AA nucleotides various cell metabolites o Different cell membranes different transport proteinsdependent on function o Each transport protein is selective it transports a specific class of molecules or even 1 specific molecule within that class o Highly specific and can distinguish very small differences in shape ofmoleculesPassive and active transporto Passive transport 1 Channel mediated gated open or close pass through down concentration gradient 2 Transporter mediated dont need NRG just need path across membraneThey specifically bind to a molecule and then undergo conformation changes that lets it across bilayer and protects it from lipid tailsActive transport against concentration gradientNeeds NRGResting membrane potential contributes to the ability of ions to move across cell membrane o Positive outside negative insideConcentration gradient and membrane potentialelectrochemical gradientwhen charged molecules are moving across the membraneTypes of active transport o Active transport is against electrochemical gradient of at least 1 moleculeYou need NRG to do this 1 Coupled transporters active transport 1 molecule is moving down the electrochem gradient which provides NRG for another molecule to transfer against the gradient 2 ATPdriven pumps use ATP hydrolysis NRG stored in phosphate bond in ATP to move molecule against gradient ATPADP 3 Lightdriven pumps bacteria they use light NRG to move molecules against the gradientTRANSPORTER PROTEINS passive transport by transporter proteins Uniporter move only 1 molecule o It binds specific solutesIt binds to moleculeThey will transport interacts in binding pocket then undergo conformational change that transports solute across membrane o Direction of transport is reversible and dependent on direction of EC gradient o Works by facilitated diffusion o Eg GULT Uniporter transports glucose across cellular membranePassive processDowngradient can work in both directionsGlucose higher in extracellular environmentActive transport by transporter proteins1 Coupled transporters a SymporterNa glucose symporter two molecules move in same direction across membraneNa glucose symporter o Na higher outside goes down electrochemical gradientSymporter moves Na into cell move glucose against concentration gradientCooperative binding the Na and glucose leads to a conformational change in the proteinopens binding pockets of intracellular environment and Na and glucose then leave protein and diffuse into intracellular environment
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