BSC 300 Lecture Notes - Lecture 9: Motor Neuron, Ranitidine, Point Mutation
16 Sep 2016
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Describe mechanisms for transporting materials across membranes: passive diffusion: simple and facilitated diffusion, active transport. Diffusion spontaneous process in which a substance moves from area of high concentration to area of low concentration until equilibrium is reached (down their concentration gradient) Permeability is the property of a membrane to allow substances to diffuse across the membrane: polarity, size, concentration and charge. Polarity: more hydrophobic, the faster the diffusing rate. Size: large molecules, like proteins, are physically blocked from diffusing across biological membranes. Concentration: molecules cannot diffuse against their concentration gradient by simple diffusion. The combination of concentration and charge constitutes an electrochemical gradient. Without considering a solute charge, the free energy change of diffusion is strictly concentration dependent: g = rt ln [ci] / [co] g = 1. 4 kcal/mol log10 [ci] / [co] For a solute that is 10 times higher outside of the cell than inside, the free energy change would be g = -1. 4 kcal/mol.
