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생리학 ( 生理學, Physiology) General Physiology Organ Physiology Integrative Physiology Physics (Physical Chemistry, Biophysics)

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( , Physiology) General Physiology Organ Physiology Integrative Physiology Physics (Physical Chemistry, Biophysics) Claude Bernard: (Homeostasis) , , pH, . Common molecular mechanisms in all forms of life Store genetic information in nucleic acids Employ proteins to catalyze chemical reactions Synthesize proteins on ribosomes Drive energy by breaking down simple sugars Use ATP as energy currency Separate cytoplasm from their environment by means of phospholipid membranes containing pumps, carriers, and channels Davson-Danielli : . Singer-Nicolson : lipid-globular protein mosaic model : . Membrane proteins Receptors Enzymes Transporters: pump, carrier, ion channels Homeostasis Electrical signalling (membrane potential) Membrane Lipid framework of biological membrane cell signalling: hormone, second messenger : , (1 F/cm 2 ) Phosphoglycerides Sphingolipids Cholesterol Glycolipids Phosphoglycerides (phospholipids) 3-carbon backbone of glycerol 2 long-chain fatty acids esterified to C1 and C2 phosphoric acid esterified to C3 : Alcohol head group . Phosphatidylethanolamine Phosphatidylcholine Phosphatidylserine phosphatidylinositol Lipid asymmetry Intercellular Junctions 4 types, each composed of a different transmembrane protein, connect the plasma membrane of adjacent cells Molecular components of cell-cell and cell-matrix junctions Adherens junctions and desmosomes Adherens junctions (zonula adherens) : cadherins anchored to actin filaments. Desmosomes (macular adherens) : cadherins anchored to intermediate filaments. Tight junctions (zonula occludens) Occlude the extracellular space between epithelial cells, forming a tight, belt-like seal that limits diffusion of water, ions, and solutes (larger than 1.8 nm). Tight junctions Tightness of the seal, reflected in electrial resistance, varies depending on cell type (extremely tight in frog skin; leaky in blood vessel); regulated by hormones (ADH, cytokines). Define the boundary between apical and basolateral membranes: two surfaces differ in lipid and protein compositions and functions. Gap junctions Two ways of intercellular communications: 1) by secreting chemical messengers; 2) direct communication by gap jucntion (electrical synapse). Connexins: proteins with 4 transmembrane helices Connexon: half channel in each membrane, made by lateral association of 6 connexins Each connexon pairs with a connexon from the adjacent cell, forming a gap junction Gap junction channels 10 nm long/1,2 nm diameter; size filter up to 1kD pass ions to establish electrochemical continuity (electrical synapse); second messengers to establish common network of information; and metabolites to allow sharing of resources Conductance: 30 to 300 pS Open/close is regulated by transjunctional potential, cytoplasmic Ca 2+, pH, cAMP- protein kinase. Gap junction closing -- terminates communication with neighboring cells that are damaged or metabolically compromised. Body Fluid Compartment

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