310_28 - CH 310 N LECTURE 28 Textbook Assignment: Chapter...

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CH 310 N LECTURE 28 Textbook Assignment: Chapter 26-Lipids Homework (for credit): HW 10 Today’s Topics: Lipids-structure; classification Notice & Announcements: Amino Acids Amino Acids and and Proteins Proteins Chapter 27
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Titration of Amino Acids Titration of Amino Acids Stage 1 Stage 1 pK pK a1 a1 H 3 N + CH 2 COOH = H 3 N + CH 2 COO - 0.5 eq OH -
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Isoelectric Point Isoelectric Point H 3 N + CH 2 COO - 1.0 eq OH - H 2 NCH 2 COO - H 3 N + CH 2 COO - = Stage 2 Stage 2 pK pK a 2 2 1.5 eq OH -
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Isoelectric point (pI): Isoelectric point (pI): the pH at which an amino acid, polypeptide, or protein has no net charge – the pH for glycine, for example, falls between the p K a values for the carboxyl and amino groups pI = 1 2 (p K a α− COOH + p K a NH 3 + ) = 2 1 (2.35 + 9.78) = 6.06 Isoelectric Point Isoelectric Point 1 2 K a p K a 3 + ) 2 1 (2.35 + 9.78) = 6.06
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6.11 5.41 5.65 6.06 6.04 6.04 5.74 5.91 6.30 5.68 5.60 5.88 6.00 p K a of p K a p K a pI ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- valine 2.29 9.72 tryptophan 2.38 9.39 9.10 2.09 threonine serine 2.21 9.15 10.60 2.00 proline phenylalanine 2.58 9.24 9.21 2.28 methionine 9.74 2.33 leucine isoleucine 2.32 9.76 glycine 2.35 9.78 9.13 2.17 glutamine 8.80 2.02 asparagine 9.87 2.35 alanine Side Chain Nonpolar & polar side chains α− NH 3 + COOH Isoelectric Point Isoelectric Point Electrophoresis: Electrophoresis: the process of separating compounds on the basis of their electric charge – electrophoresis of amino acids can be carried out using paper, starch, polyacrylamide and agarose gels, and cellulose acetate as solid supports Electrophoresis Electrophoresis
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1. a sample of amino acids is applied as a spot on the paper strip 2. an electric potential is applied to the electrode vessels and amino acids migrate toward the electrode with charge opposite their own 3. molecules with a high charge density move faster than those with low charge density Electrophoresis Electrophoresis ¾ molecules at their isoelectric point remain at the origin ¾ after separation is complete, the strip is dried and developed to make the separated amino acids visible ¾ 19 of the 20 amino acids give the same purple-colored anion; proline gives an orange-colored compound Electrophoresis Electrophoresis
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a reagent commonly used to detect amino acid is ninhydrin ninhydrin RCHCO - O OH O O NH 3 + O O - N O O O RCH CO 2 H 3 O + + An
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This note was uploaded on 02/03/2012 for the course CH 310 N taught by Professor Blocknack during the Fall '08 term at University of Texas at Austin.

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310_28 - CH 310 N LECTURE 28 Textbook Assignment: Chapter...

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