haun71 - Medical Biochemistry Membranes: Bilayer...

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Medical Biochemistry Membranes: Bilayer Properties, Transport Lecture 71
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Membrane function Serve as barriers to separate contents of cell from external environment or contents of organelles form remainder of the cell Proteins in cell membrane have many functions transport of substances across the membrane enzymes that catalyze biochemical reactions receptors on exterior surface that bind external ligands ( e.g., hormones, growth factors) mediators that aid ligand-receptor complex in triggering sequence of events ( second messengers that alter metabolism are produced inside the cell)
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Plasma membrane has selective permeabilities Channels and pumps for ions and substrates Specific receptors for signals ( e.g., hormones) Exchange materials with extracellular environment exocytosis and endocytosis
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Membranes form specialized compartments Organelles with specialized functions e.g., mitochondria, ER, Golgi complex Localize enzymes Excitation-response coupling Energy Transduction photosynthesis, oxidative phosphorylation
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Internal Water Is Compartmentalized Intracellular Fluid (2/3 of total water) rich in K + and Mg 2+ , phosphate major anion protein higher Extracellular Fluid (1/3 of total water) high Na + and Ca + , chloride major anion glucose higher
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Composition of membranes varies within and between cells Major lipids in mammalian membranes Phospholipids Glycosphingolipids Cholesterol
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Phospholipids - two major classes 1. phosphoglycerides are more common glycerol backbone two fatty acids in ester linkage usually even-numbered carbons (C16, C18) unbranched, either saturated or unsaturated C18 or 20:4, 5,8,11,14 phosphorylated alcohol phosphatidic acid (1,2-diacylglycerol 3- phosphate) is simplest -- key intermediate in formation of all other phospholipids
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Phospholipids - two major classes 2. sphingomyelins sphingosine backbone (rather than glycerol) fatty acid attached by amide linkage primary hydroxyl group of sphingosine esterified to phosphocholine prominent in myelin sheaths
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Glycosphingolipids sugar-containing lipids e.g., cerebrosides and gangliosides also derived from sphingosine differ from sphingomyelin in group attached to primary hydroxyl group of sphingosine sphingomyelin - phosphocholine cerebroside - single hexose (glucose or galactose) ganglioside - chain of 3 or more sugars (at least one is sialic acid)
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Sterols most common sterol cholesterol almost exclusively in plasma membrane lesser amounts in mitochondria, Golgi, nuclear membranes generally more abundant toward outside of plasma
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This note was uploaded on 12/24/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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haun71 - Medical Biochemistry Membranes: Bilayer...

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