AT Lecture 3

# AT Lecture 3 - BISC 330L: Biochemistry Spring Semester 2012...

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BISC 330L: Biochemistry Spring Semester 2012 USC Lecture: Friday, 13 January 2012 1. Finish Chapter 1 material… Henderson-Hasselbalch Discovery of DNA The Genomic Revolution

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Henderson-Hasselbalch Equation For acid AH (proton donor in neutral form): AH A - + H + K a = [A - ][H + ]/[AH] logK a = log[H + ] + log([A - ]/[AH]) - log[H+] = -logK a + log([A - ]/[AH]) pH = pK a + log([A - ]/[AH]) (Henderson-Hasselbalch Equation) NOTE: [A - ]/[AH] = 10 pH-pKa [A-] = [AH](10 pH-pKa ) [AH] = [A-]/(10 pH-pKa ) Fraction ionized (f I = f A -):
pH f i = f A = 10 pH-pKa /(1+10 pH-pKa ) -3 + pKa 10 -3 / (1+10 -3 ) = 0.001 -2 + pKa 10 -2 / (1+10 -2 ) = 0.01 -1 + pKa 10 -1 / (1+10 -1 ) = 0.1 pKa 1 / (1+1) = 0.5 1 + pKa 10 1 / (1+10 1 ) = 0.9 2 + pKa 10 2 / (1+10 2 ) = 0.99 3 + pKa 10 3 / (1+10 3 ) = 0.999 Fraction ionized (f I = f A -): f I = [A - ]/([A - ]+[AH]) = (10 pH-pKa )/(1 + 10 pH- pKa )

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Graph of the data f i pH - 3 + p K a 2 1
Summary of Henderson-Hasselbalch Equation For base B (proton acceptor in neutral form): BH + B + H + K a = [B][H + ]/[BH + ] logK a = log[H + ] + log([B]/[BH + ]) pH = pK a + log([B]/[BH + ]) (Henderson-Hasselbach Equation) NOTE: [B]/[BH + ] = 10 pH-pKa

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pH f i = f BH+ = 1 / (1+10 pH-pKa ) -3+pKa 1 / (1+10 -3 ) = 0.999 -2+pKa 1 / (1+10 -2 ) = 0.99 -1+pKa 1 / (1+10 -1 ) = 0.9 pKa 1 / (1+1) = 0.5 1+pKa 1 / (1+10 1 ) = 0.1 2+pKa
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## This note was uploaded on 03/15/2012 for the course BISC 330L taught by Professor Petruska,tower during the Spring '07 term at USC.

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AT Lecture 3 - BISC 330L: Biochemistry Spring Semester 2012...

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