lecture 21 - BIO 311C March 5 2008 Exam 2 Friday March 7 in...

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BIO 311C March 5, 2008 Exam 2: Friday, March 7, in this room Jingjie has assembled some structural formulas of molecules and a few questions that you may review to help prepare for Exam 2. They are found under “Discussion Section Information” on the course web site.
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Mechanisms of Transport Across Biological Membranes 2. Specific transport of individual molecules A. Water B. Facilitated diffusion i. permease-mediated ii. ionophore-mediated C. Active transport i. permease-mediated ii. electron-transport mediated 3. Bulk transport A. Endocytosis B. Exocytosis * 1. Non-specific transport of small nonpolar molecules
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Small nonpolar molecules such as short-chain hydrocarbons easily pass through biological membranes, but often disrupt and may even dissolve the membrane as they pass through. illustration of small nonpolar molecules such as those which occur in gasoline Fortunately, we seldom come into contact with these kinds of molecules. The keratin surface on skin provides temporary protection from membrane exposure to small nonpolar molecules. *
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Gasses such as O 2 , CO 2 and N 2 require no special mechanism to pass through biological membranes because they are very small and are quite nonpolar. Both O 2 (molecular oxygen) and CO 2 (carbon dioxide) must be transported across cellular membranes rapidly for efficient respiration and photosynthesis. N 2 (dinitrogen gas) is completely inert in most kinds of cells and has very little influence on cellular activities. transport rapidly across the membrane in both directions without altering the membrane *
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Transmembrane proteins with transport-enabling functions greatly expand the range of chemical substances that pass through biological membranes Each different transport-enabling protein allows transport across the membrane of only one or a very few kinds of chemical substances. * The highly specific transport- enabling proteins are called permeases.
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Biological membranes contain many copies of a permease called aquaporin , which facilitates very rapid movement of water across the membrane.
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