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Chapter 22 Biochemistry 491 22.57 Peptide bonds are formed when the carboxylic end of one amino acid reacts with the amine end of another amino acid. (a) Gln - - Met - Cys H 0 H H 0 C C N C C N C C OH H H CH₂ CH₂ CH₂ CH₂ CH₂ SH S NH₂ CH₃ (b) Ser - Leu Cys H 0 H 0 H 0 H₂N C C N C C N C C OH H H CH₂ CH₂ CH₂ OH H₃C CH SH CH₃ (c) Cys Leu - Ser H H 0 H 0 C C N C C N C C OH H H CH₂ CH₂ CH₂ SH H₃ C CH OH CH₃ 22.59 This would be a tertiary structure. Tertiary structure refers to the large-scale twists and folds of globular proteins. These are maintained by interactions between the R groups of amino acids that are separated by long distances in the chain sequence. 22.61 This would be a primary structure. Primary structure is simply the amino acid sequence. It is maintained by the peptide bonds that hold amino acids together. Nucleic Acids 22.63 (a) Yes, it is a nucleotide and the base is A, adenine. (b) No, it is not a nucleotide; it is the base A, adenine. (c) Yes, it is a nucleotide and the base is T, thymine. (d) No, it is not a nucleotide; it is the amino acid methionine. 22.65 The two purine bases: Adenine Guanine NH₂ 0 N N N HN N N N H N H Copyright © 2017 Pearson Education, Inc.