chapter 7 - Lipid Bilayer of the Cell Membrane Membrane...

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1 Membrane Structure and Function Lipid Bilayer of the Cell Membrane Two back-to-back layers phospholipid molecules Æ CM total: lipids (50%) and proteins (50%). Cholesterol and glycolipids scattered among the double row of phospholipids Hydrophilic head WATER Hydrophobic tail WATER Hydrophilic region of protein Æ polar aa Hydrophobic region of protein Æ non-polar aa Phospholipid bilayer EXTRACELLULAR SIDE N-terminus Structure of a transmembrane protein C-terminus CYTOPLASMIC SIDE α Helix Knife Extracellular layer Proteins Freeze-fracture technique Æ splits a membrane along the phospholipid bilayer Cytoplasmic layer Extracellular layer Cytoplasmic layer Plasma membrane
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2 Types of Membrane Proteins Integral proteins extend into or completely across cell membrane if extend completely across = transmembrane proteins amphi-pathic Æ hydrophobic portions hiding among the phospholipid tails Peripheral proteins attached to either inner or outer surface of cell membrane Membrane Proteins Integral versus Peripheral Proteins Functions of Membrane Proteins Enzymes Signal Receptor ATP Transport Enzymatic activity Signal transduction remember cellular junctions Glyco- protein Cell-cell recognition Intercellular joining Attachment to cytoskeleton & extra- cellular matrix (ECM) Membrane Fluidity Membranes are fluid structures (oil layer) self-sealing if punctured with needle Fluidity: membrane molecules can rotate & move freely need to stay in one half of lipid bilayer fluidity is reduced by presence of cholesterol increases stiffness of membrane it forms hydrogen bonds with neighboring phospholipid heads Cholesterol Cholesterol within the animal cell membrane
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3 Selective Permeability of Membrane Lipid bilayer permeable to nonpolar , uncharged molecules Æ steroids permeable to wate pola ) which flows through permeable to water ( polar ) which flows through gaps that form in hydrophobic core of membrane
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chapter 7 - Lipid Bilayer of the Cell Membrane Membrane...

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