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Chapter 23
Amino Acids, Peptides, and Proteins

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23-00CO
Title
 Oxidized Glutathione
Caption
 Ball-and-stick model of oxidized glutathione.
Notes
 Oxidized glutathione is a tripeptide with a disulfide linkage connecting two molecules. The reduced form is used to keep sulfhydryl groups in proteins from forming disulfide links.
Keywords
 oxidized, glutathione, ball-and-stick
23-00-22UN
Title
 Glycine, Leucine, Aspartate, and Lysine
Caption
 Potential maps of glycine, leucine, aspartate, and lysine.
Notes
 Glycine is hydrophilic, leucine is hydrophobic, aspartate is acidic, and lysine is a basic amino acid.
Keywords
 Glycine, Leucine, Aspartate, Lysine
23-00-29UN
Title
 Alanine
Caption
 Ball-and-stick model of l-alanine.
Notes
 l-Alanine is one of the 20 natural amino acids used by nature to build proteins.
Keywords
 alanine, ball-and-stick,
23-01
Title
 Figure 23.1
Caption
 Arginine, alanine, and aspartic acid separated by electrophoresis at pH = 5.
Notes
 Amino acids can be separated according to their pI values using electrophoresis. Amino acids having pI values greater than the pH of the electrophoresis buffer migrate toward the negative electrode, and amino acids having pI values lower than the pH value of the electrophoresis buffer migrate toward the positive electrode.
Keywords
 figure, 23.1, electrophoresis
23-02
Title
 Figure 23.2
Caption
 Separation of glutamate, alanine, and leucine by paper chromatography.
Notes
 Since paper is a carbohydrate polymer (very hydrogen-bonding) the most polar amino acids migrate the slowest.
Keywords
 figure, 23.2, glutamate, alanine, leucine, paper, chromatography
23-03
Title
 Figure 23.3
Caption
 Structure of a section of a cation-exchange resin called Dowex 50.
Notes
 Cation-exchange resins will release cations and impede cationic amino acids by replacing the released cations with the cationic amino acids. Anion-exchange resins will do the reverse.
Keywords
 figure, 23.3, cation-exchange, resin
23-04
Title
 Figure 23.4
Caption
 Separtaion of amino acids by ion-exchange chromatography.
Notes
 A mixture of amino acids is run through an ion-exchange resin and fractions are collected in separate sample tubes. The concentration of amino acid in each tube is measured with ninhydrin and plotted vs. sample number. Enough fractions are collected so that each amino acid is collected in several tubes and separated from all other amino acids.
Keywords
 figure, 23.4, separation, amino, acids, ion-exchange, chromatography
23-05
Title
 Figure 23.5
Caption
 Chromatogram obtained from an automated amino-acid analyzer.
Notes
 Buffers of increasingly higher pH are used to elute amino acids having sidechains with increasingly higher pKa values. Shown in the figure is a chromatogram using a cation-exhange resin. Acidic (anionic) amino acids elute before hydrophobic amino acids, which elute before basic (cationic) amino acids.
Keywords
 figure, 23.5, amino-acid, analyzer, chromatogram
23-07-01UN
Title
 Intrachain and Interchain Disulfide Bridges
Caption
 Schematic of polypeptide chains showing interchain and intrachain disulfide bridges.
Notes
 Intrachain disulfide bridges bond together different parts of the same polypeptide molecule. Interchain disulfide bridges bond together different polypeptide molecules.
Keywords
 intrachain, interchain, disulfide, bridges, polypeptide
23-08a
Title
 Figure 23.8
Caption
 a. Side view of a protein segment with an a-helix structure. b. Longitudinal view of a protein segment with an a-helix structure.
Notes
 The a-helix structure is a secondary structure held together by amide N–H to amide carbonyl hydrogen bonding in the backbone of the protein molecule.
Keywords
 figure, 23.8, a-helix, side, longitudinal, protein
23-10
Title
 Figure 23.10
Caption
 Backbone secondary structure of carboxypeptidase A.
Notes
 a-Helical sections are purple. b-Sheet sections are flat green arrows pointing toward the carboxy terminus of the protein.
Keywords
 figure, 23.10, backbone, secondary, structure, carboxypeptidase
23-11
Title
 Figure 23.11
Caption
 Stabilizing interactions involved in maintaining the tertiary structure of a protein.
Notes
 Tertiary structure is maintained by interactions between sidechains of different amino acids within the same protein molecule.
Keywords
 figure, 23.11, tertiary, structure, protein
23-12
Title
 Figure 23.12
Caption
 Three-dimensional structure of carboxypeptidase A.
Notes
 Carboxypeptidase A, an elliptically shaped protein made from 307 amino acids, is used by the body to digest protein in the upper GI tract.
Keywords
 figure, 23.12, carboxypeptidase, three-dimensional, structure
23-13-02P42
Title
 End-of-Chapter Problem 42
Caption
 Two-dimensional chromatogram associated with end-of-chapter Problem 42.
Notes
 Identify the six amino acid spots in the two-dimensional chromatogram by calculating pI values for the six amino acids listed in the problem and arranging the amino acids with pI values near 5 in order of relative polarity.
Keywords
 end-of-chapter, problem, 42, two-dimensional, chromatogram
23-13-03P51
Title
 End-of-Chapter Problem 51
Caption
 Two-dimensional chromatogram associated with end-of-chapter Problem 51.
Notes
 Identify the amino-acid spots on the two-dimensional chromatogram by calculating pI values for the 15 amino acids listed in the problem, and by comparing polarities. Two of the amino acids do not separate. They form a single spot.
Keywords
 end-of-chapter, problem, 51, two-dimensional, chromatogram
23-13-05P54
Title
 End-of-Chapter Problem 54
Caption
 UV spectra associated with end-of-chapter Problem 54.
Notes
 Use the UV spectra of tryptophan, tyrosine, and phenylalanine shown in the figure to calculate the molar absorptivity of each of these amino acids at 280 nm.
Keywords
 end-of-chapter, problem, 54, UV, spectra
23-13-06P55
Title
 End-of-Chapter Problem 55
Caption
 Two-dimensional chromatograms associated with end-of-chapter Problem 55.
Notes
 Look at the two-dimensional chromatogram of the amino acids composing a mutant polypeptide on the right side of the figure. Find the amino-acid spot which is missing from the normal polypeptide two-dimensional chromatogram on the left, and find the amino-acid spot which is only found in the mutant polypeptide chromatogram on the right. These differences are due to the presence of a replacement amino acid found in the mutant polypeptide in place of the amino acid missing in the normal polypeptide. Determine whether the replacement amino acid is more or less polar than the normal amino acid, and determine whether the replacement amino acid has a higher or lower pI value than the normal amino acid.
Keywords
 end-of-chapter, problem, 55, two-dimensional, chromatograms

Title
 Table 23.1 The most Common Naturally Occuring Amin Acids pt1
Caption
Notes
Keywords
23-TB01pt2
Title
 Table 23.1 The most Common Naturally Occuring Amin Acids pt2
Caption
Notes
Keywords

Title
 Table 23.1 The most Common Naturally Occuring Amin Acids pt3
Caption
Notes
Keywords

Title
 Table 23.2 The pK2 Values of Amino Acids
Caption
Notes
Keywords

Title
 Table 23.3 Specificity of Peptides of Protein Cleavage
Caption
Notes
Keywords
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