Lecture 2 outline - Lecture 2, January 21, 2010 Things I...

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Lecture 2, January 21, 2010 Things I did not talk about last time, but that are in the notes Nissl Stain Chromatolysis Last time: Saw the nervous system operated by 2 kinds of potentials: local and action potentials. These potentials occur across the cell membrane; they represent a change in a voltage between the inside and outside of the cell. There are voltages between the inside of a cell and its outside. That is to say, in the same sense if I took two wires, connected them to the terminals of a battery and to a light bulb--the battery has a voltage. This voltage will drive current flow through the light bulb. The same will happen if we took two wires, placed one of them outside a cell and the other inside a cell and connected these wires through a light bulb: the cell would drive a current through the light bulb. We need to understand what this means and how it comes about. Cell membrane Structure of a cell membrane Structure of cell membrane: a bimolecular leaflet of lipids with non-polar, hydrophobic tails of lipids constituting the central portion of the membrane, and the polar ends of these molecules facing the intracellular and extracellular fluids. Embedded in the membrane are intrinsic proteins that may or may not span the membrane, and extrinsic membrane proteins that are bound to the intracellular and extracellular surfaces of the membrane. Function of the cell membrane To act as a barrier and to provide for the concentration of molecules that make life possible However, it is necessary for a cell to exchange materials across this membrane. Both to take up nutrients and to get rid of wastes. But even down to simple molecules like ions and water. It is primarily the water and ions that concern us today. Solutions are present on each side of the membrane We can talk about an intracellular solution/fluid and an extracellular solution/fluid. You would expect these solutions to differ in their composition of proteins, nucleic acids and other macromolecules that define life. What is less obvious is that the solutions differ in
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their composition of basic salts, particularly Na, K, Cl. How do molecules move in solution? Diffusion the process whereby particles of liquids, gases, or solids intermingle as the result of their spontaneous movement caused by thermal agitation and in dissolved substances move from a region of higher to one of lower concentration Example: what happens when we drop a crystal say of sucrose into water movement occurs down concentration gradient (increasing entropy) By the second law of thermodynamics this is the direction we expect all processes in the universe to go--no energy needs to be supplied to actually achieve this movement. Just the random kinetic energy of the molecules themselves will provide for the movement. However to go in reverse direction (i.e. to concentrate this molecules from such a
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This note was uploaded on 02/01/2010 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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Lecture 2 outline - Lecture 2, January 21, 2010 Things I...

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