Amino Acids

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Chapter 4 . Amino Acids 48
Chapter 4 . Amino Acids Problems and Solutions 1. Without consulting chapter figures, draw Fisher projection formulas for glycine, aspartate, leucine, isoleucine, methionine, and threonine. Answer: Glycine + H3N COO- C H H Aspartate COO- + H3N C H CH 2 COO- Leucine COO- + H3N C H CH 2 CH H3C CH3 49 Isoleucine COO- + H3N C H H 3C C H CH 2 CH 3 Methionine COO- + H3N C H CH 2 CH 2 S CH 3 Threonine COO- + H3N C H 2. Without reference to the text, give the one-letter and three-letter abbreviations for asparagine, arginine, cysteine, lysine, proline, tyrosine, and tryptophan. Answer: For many of the amino acids the l letter code is the first letter of the amino acid. Problems arise when two amino acids start with the same letter. Whenever this occurs, the amino acid with the lowest molecular weight is assigned the letter. The other amino acid is given a phonetic letter or the closest unused letter in the alphabet. The amino acids assigned their first letters are: Glycine, Alanine, Valine, Leucine, Isoleucine, Serine, Threonine, Proline, Cysteine, Methionine and Histidine. Aspartic acid is D, an easy way to remember it is to pronounce it as "asparDic" acid. Glutamic acid is E, E follows D, glutamic acid follows aspartic acid in chemical structure. E is also the closest unused letter to G. F is for phenylalanine, (Fenylalanine). R is for arginine, remembered by pronouncing arginine (Rginine). N is for asparagine; remember to stress the N sound. Glutamine follows asparagine, its l letter code is the next unused consonant after N, namely Q. Lysine is K, the closest unused letter to L. Tyrosine is Y; Y is the dominant sound in tyrosine. Tryptophan is W; remember "double ring, double you". 3. Write equations for the ionic dissociations of alanine, glutamate, histidine, lysine, and phenylalanine. Answer: Alanine dissociation: COOH Glutamate Dissociation: + H3N C H COOH + H3N C H CH 2 CH 2 COOH CH 3 COO- + H3N C H CH 2 CH 2 COOH COO- + H3N C H CH 3 COO- + H3N C H CH 2 CH 2 COO- NH 2 COO- C H CH 3 NH 2 H COO- C H CH 2 CH 2 C COO- CH 3 OH
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