BIOC 3560 Lecture Notes - Lecture 16: Morphine, Cytosol, Glycerol
23 Apr 2019
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Ions and polar molecules cannot cross (essentially impermeable: eg. Small, uncharged, somewhat polar molecules can cross: eg. glycerol, ethanol. Hydrophobic molecules, gases cross quickly: eg. O2, co2, n2: cholesterol based steroid hormones, most drugs are hydrophobic. Morphine somewhat polar, acetylated morphine = heroin, more hydrophobic, crosses membranes faster. Ionic composition of cytosol is different from extracellular environment: cytosol: more k+, less na+, less ca2+ There are ion concentration gradients: across plasma membranes, across organelle membranes. Free energy of solution (concentration = c: g = go + rt ln c. Negative g when molecules move from high concentration to low concentration: g = rt ln c2 rt ln c1 = rt ln (c2/c1) If c1 > c2, ln (c2/c1) is negative, so g is negative: conversely, this much energy is required ( g positive) to maintain this chemical gradient. Diffusion occurs spontaneously (high to low concentration) c1 = c2 at equilibrium.
