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PSU BMB 251 - Membrane Structure: the Lipid Bilayer
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BMB 251 1st Edition Lecture 27 Outline of Last Lecture I. Clicker QuestionII. Leucine Zipper III. ActivatorsIV. RepressorsV. TryptophanVI. Lac Operon/RepressorVII. Gene Regulatory ProteinsVIII. Gene Activators/RepressorsOutline of Current Lecture IX. Clicker QuestionX. Plasma MembraneXI. Lipid BilayerXII. PhospholipidsCurrent Lecture- Clicker Question 1: Which is the least likely to diffuse through a pure bilayer (i.e., containing only phospholipids with no embedded proteins)?o H2Oo O2o Glucoseo Na+ -single ions cannot cross the membrane by themselves- Plasma membrane: encloses cell, define its boundaries and maintains essential differences between cytosol and extracellular environment- Protein receptors: transport information (rather than molecules) across the membrane- All biological membranes have a common general structure: very thin film of lipid (fatty) and protein molecules, held together mainly by noncovalent interactions - Cell membranes: dynamic, fluid structures with double lipid layers (aka lipid bilayer)o Relatively impermeable barrier to passage of most water-soluble molecules- Lipid bilayer: provides basic structure for all cell membraneso Lipid molecules are amphiphilic (have both a hydrophobic and a hydrophilic end)o Most abundant membrane lipids: phospholipids- have a polar head group and two hydrophobic hydrocarbon tails (usually fatty acids)  one usually contains one or more -cis double bonds, making it unsaturated and kinked, while the other tail does not Main phospholipids: phosphoglycerides- three carbon-glycerol backboneo Lipid bilayers also contain cholesterol (rigid ring structure with one polar –OH group and short hydrocarbon tail) and glycolipids These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Phospholipids aggregate spontaneously into either spherical micelles or bilayers (more energetically favorable)o Bilayers are about 5 nm thicko Each layer of the bilayer is called a leafleto Lipids diffuse readily within the plane of the bilayer, but will not flip from one leaflet to another (without some sort of assistance from a specific transport


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PSU BMB 251 - Membrane Structure: the Lipid Bilayer

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