Lecture4 - BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS,...

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1 The Amino Acids, and the Covalent Structure of Proteins BIOCHEM 227 FALL 2010 Lecture 4 Monday, September 6, 2010 TODAY •Con t inu e : pH and pK a • The amino acids • The covalent structure of proteins BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS, COVALENT STRUCTURE OF PROTEINS 6 SEP 2010
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2 pK a What is pK a ? –pK a is a shorthand for the equilibrium constant for the deprotonation of a substance when dissolved in water – A negative log means an inverse relationship Higher pK a means lower K a means less reaction Lower pK a means higher K a means more reaction + ⎤⎡ ⎦⎣ =− a HA pK log log HA a K pK a •pK a is a measure of degree of deprotonation of a substance when dissolved in water a is a measure of a the relative affinity for protons at a particular protonation site BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS, COVALENT STRUCTURE OF PROTEINS 6 SEP 2010
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3 pH •pH m e a su r e s [H + ] – log scale: +1 pH unit is 10x more H + – defined as + ⎡⎤ =− ⎣⎦ pH log H pH BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS, COVALENT STRUCTURE OF PROTEINS 6 SEP 2010
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4 pH and pK a • In aqueous systems, the Henderson- Hasselbalch Equation relates [H + ] (pH) to [A - ] and [HA]. =+ a A pH pK log HA BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS, COVALENT STRUCTURE OF PROTEINS 6 SEP 2010
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5 Henderson-Hasselbalch Example • Example: proton-containing substance HA with pK a of 7 dissolved into water at pH 7 =+ ⎡⎤ ⎣⎦ = = a A pH pK log HA A 77l o g HA A 0l o g HA A 1 HA BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS, COVALENT STRUCTURE OF PROTEINS 6 SEP 2010
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6 =+ ⎡⎤ ⎣⎦ −= = a 5 A pH pK log HA A 27l o g HA A 5l o g HA A
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This note was uploaded on 12/19/2010 for the course BIOCHEM 227 taught by Professor Coggins during the Fall '10 term at Duke.

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Lecture4 - BCH 227 FALL 2010 LECTURE 4: THE AMINO ACIDS,...

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