Question 5 of 8 Lehninger Principles of Biochemistry Nelson I Cax MHE/Freeman pr

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Question 5 of 8 Lehninger Principles of Biochemistry Nelson I Cax MHE/Freeman preserted by Sapling Leaming Mixtures of amino acids can be analyzed by separating the mixture into its components through ion- exchange chromatography. Amino acids placed on a cation-exchange resin containing sulfonate (-SO3) roups flow down the column at different rates because of two factors that influence their movement: (1) onic attraction between the sulfonate groups on the column and positively charged functional groups on the amino acids, and (2) hydrophobic interactions between amino acid side chains and the strongly hydrophobic backbone of the polystyrene resin. For each pair of amino acids listed, determine the order of elution from a cation exchanger in pH 7.0 buffer. Amino Acid Pairlutes First Elutes Second Asp and Lys Arg and Leu Ala and Glu Gly and Met Phe and Ser Aspe Glu Ser Gly Lys Arg Ala Met Phe

Explanation / Answer

Amino acid pair:

1. Asp and Lys: Asp will eleute first and then lysin because asp has negative charge and lysin has positive charg at pH 7. A repulsion will occur between negative charge of sulphonate and aspartic acid and thus asp will elute first.

2. Arg and Leu: Leucin will elute first because leucine has not any kind of charge while arg has positivie charge and thus arginine movement will be inhibited by both negative charge of sulphonate and hydrphobic interaction while leucin movement will be inhibited only by hydrophobic interaction.

3. Ala and Glu: Glutamic acid will elute first because it has negative charge while alanine has not any charge at pH 7.

4. Gly and Met: Here both amino acids are hydrophobic but the size of methionine is greater than glycine and thus it will experience more hydrophobic interaction and thus will elute later.

5. Phe and ser: Serine will elute fisrt. Although serine and phenylalanine both are unchrged amino acid but serine has some polarity which reduces its hydrophobicity.

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