Topic%2002%20_%20Buffers%20_%20F10

Topic%2002%20_%20Buffers%20_%20F10 - Buffers Buffer: Is a...

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Buffers Buffer: Is a mixture of a weak conjugate acid and its weak conjugate base in solution that resists changes in pH when an acid or base are added HA + OH - A - + H 2 O A + H + HA
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Cysteine Histidine Lysine Arginine Aspartic acid Glutamic acid –OH –O –SH –S C–N C–N CH H H + H C–N C–N CH H H –NH 3 + –COOH –COOH –COO –COO ε β γ PROTONATED DEPROTONATED =NH 2 + –NH 2 =NH Buffers WHY ? Maintain Protein Structure
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Buffers WHY ? Maintain Protein Function adapted from: http://porpax.bio.miami.edu/~cmallery/255/255enz/enzymology.htm
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Weak Acid Dissociation HA H + + A k –1 k 1 K eq = [H + ] [A ] [HA] = K a (the ionization constant) pH [HA] [A ] = pK a + log Henderson-Hasselbalch equation
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which depends on: the total molarity, [buffer] = [A ] + [HA] the pH of the solution relative to the pK a ie, the ratio [A ] / [HA] BUFFER CAPACITY: the ability of a buffer to resist pH changes and
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Buffer Capacity buffer capacity in the acid direction, adding acid: BC A [A]/[HA] converting A to HA with H + [A] decrease = [HA] increase buffer capacity in the base direction, adding base: BC B [A]/[HA] converting HA to A with OH - [HA] decrease = [A] increase
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7.09 6.91 0.5 M pK a = 7.0 [HA] + [A - ] = 0.1 M or 0.5 M pH 0.025 0.0125 0 0.0125 0.025 Moles H + Moles OH - 6 8 7 No Buffer 0.1 M 6.52 7.47
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This note was uploaded on 11/21/2010 for the course MCB 120L 69059 taught by Professor Fairclough during the Fall '10 term at UC Davis.

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Topic%2002%20_%20Buffers%20_%20F10 - Buffers Buffer: Is a...

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