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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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