2.2_Cell_Biology_II - Now, we will continue our odyssey...

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Unformatted text preview: Now, we will continue our odyssey within the cell. 1 In this presentation, we look at cell membranes and how materials cross the membrane. Also, we will examine cellular energy and how ATP is used to power reactions. Most chemical reactions in the cell are facilitated through enzymes and this will be explained. 2 First, cell membranes. Phospholipids were introduced last week and as you recall, the phosphate containing portion is hydrophilic, that is attracted to water, and the two fatty acids are hydrophobic. As a consequence of this structure, the phospholipids form a double layer as shown. Embedded in the bilayer are proteins that have many different functions. 3 These are some of the more important membrane protein functions. We will cover specific examples of these as we go through the course. 4 This illustration displays the plasma membrane and extracellular matrix of an animal cell. The functions listed in the previous slide are illustrated. Shape of the cell in animals is maintained with structural membrane proteins called integrins and their connection to cytoskeleton elements that were discussed in the previous presentation. Note also, the specific binding of the sugar-protein compound called a glycoprotein to another cells membrane protein; these are critical in cell to cell recognition that needed by an organism such as with the immune system. The illustration also shows different proteins functioning to transport materials, both passively and actively; this will be our next topic. 5 Now, lets consider the transport of materials across cellular membranes . This are the topics we will overview. 6 Diffusion is a general concept referring to the tendency of materials to spread out over space. In solutions, this is observed as solutes diffuse evenly throughout the solution. The movement of solutes would constitute passive transport because no active process is employed to move the atoms or molecules. Importantly, passive diffusion results in solutes diffusing from areas of high concentration to areas of low concentration; this is called diffusing down their concentration gradient. 7 8 Biological membranes allow passage of some molecules and not to others. Whether the membrane is a barrier or not depends on chemical characteristics of both the membrane and the solute as well as physical attributes such as the size of the solute. Diffusion of a solute across a membrane is always two-way; however, when the concentration of the solute is greater on one side of the membrane, a diffusion gradient exists and there will be a greater number of molecules moving to the less concentrated side than vice versa . This will continue to occur until the concentrations are equal, thus equilibrium is reached. are equal, thus equilibrium is reached....
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This note was uploaded on 01/29/2012 for the course BIOL 212 taught by Professor Rockhill during the Spring '08 term at Seattle Central Community College.

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2.2_Cell_Biology_II - Now, we will continue our odyssey...

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