Lecture 11.Feb15 - BIO 311C Spring 2010 Graded exams will...

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BIO 311C Spring 2010 Lecture 11 – Monday 15 Feb. Graded exams will be returned during discussion periods on Friday and next Monday. A Key to Exam 1 will be placed on the course web site on Wednesday. 1
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Many Biological molecules have positive and negative charges simultaneously. Consider a molecule in the cytoplasmic matrix of a cell ( ~pH 7) that contains three ionizable functional groups : Note: This molecule would have 3 electric charges about half of the time and 4 electric charges about half of the time. organic molecule * Review 2
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If only one or a very few molecules with an ionizable functional group are placed into a compartment of a cell, then the pH (the relative amounts of H 3 O + and OH - ) of the compartment prior to the addition of the molecules will determine the ionization state of the functional group. If a large number of molecules with an ionizable functional group are placed into a compartment of a cell (large enough to make its concentration of the functional group as high or higher than the concentration of H 3 O + or OH - ), then the pH of the compartment will be affected by the functional group of the molecules. Effects of Adding Molecules with an Ionizable Functional Group to a Compartment of a Cell * 3
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pH Buffer: A chemical buffer that resists a change in the concentration of H 3 O + in an aqueous solution. Definitions: Buffer: an agent that prevents or retards a change in the state of a chemical or physical system. Chemical Buffer: a chemical substance agent resists a change in concentration of some other chemical substance in a solution. note: In molecular biology "buffer" always means "pH buffer” unless stated otherwise. note: “Although not strictly accurate, the concentration of H 3 O + " is sometimes written in more abbreviated form as "the concentration of H + ", or as “[ H + ]”. * note: in order to act as an effective pH buffer, the concentration of the functional
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Lecture 11.Feb15 - BIO 311C Spring 2010 Graded exams will...

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