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Unformatted text preview: Amino Acids Chapter Amino acids: monomeric units of proteins α-amino acids: standard amino acids that all have, except for proline, a primary amino group and a carboxylic acid group substituent on the same carbon atom In the physiological pH range, both the carboxylic acid and the amino groups of α- amino acids are completely ionized . Amphoteric: the ability to act as an acid or a base Ampholytes ( ampho teric electro lytes ): a substance that can act as an acid or a base Zwitterions (Dipolar ions): molecules that bear charged groups of opposite polarity Peptide bond: a CO—NH linkage in which a condensation reaction occurs Amino acid residues (peptide units): an amino acid molecule that has condensed when joining to another amino acid Dipeptides: two amino molecules Tripeptides: three amino molecules Oligopeptides: 3-10 amino molcules Polypeptides: many amino acid residues often referred to as peptides Proteins are molecules that consist of one or more polypeptide chains. Polypeptides are linear polymers. The various organisms on Earth collectively synthesize an enormous number of different protein molecules whose great range of physicochemical characteristics stem largely from the varied properties of the 20 “standard” amino acids R groups: side chains on an amino acid Glycine: first amino acid identified and has the smallest possible side chain, an H atom Alanine: methyl group side chain Valine: isomeric propyl group side chain Leucine: isomeric butyl group side chain Isoleucine: isomeric butyl group side chain Amino Acids Chapter Methionine: a thiol either side chain that resembles an n-butyl group in many of its physical side chains Proline: a cyclic secondary amino acid, has conformation constraints imposed by the cyclic nature of its pyrrolidine side group Phenylalanine: a phenyl moiety side chain, an aromatic side group Tryptophan: an indole group side chain, an aromatic side group Serine: hydroxylic R group Threonine: hydroxylic R group Asparagine: has an amide-bearing side chain, amide of aspartic acid Glutamine: has an amide-bearing side chain, amide of glutamic acid Tyrosine: has a phenotic group...
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