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Transcript
24.9 Synthesis of Amino Acids Plants and bacteria produce all of their amino acids using NH4+ and NO3–. • Humans can synthesize 9 of the 20 amino acids found in their proteins. • Nonessential amino acids are synthesized in the body, while essential amino acids must be obtained from diet. Learning Goal Illustrate how some nonessential amino acids are synthesized from intermediates in the citric acid cycle and other metabolic pathways. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Pathways for Amino Acid Synthesis A variety of pathways are involved in the synthesis of nonessential amino acids. • The body synthesizes nonessential amino acids. • The α-keto acid carbon skeletons are obtained from the citric acid cycle or glycolysis and converted to amino acids by transamination. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Synthesis of Amino Acids Nonessential amino acids are synthesized from intermediates of glycolysis and the citric acid cycle. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Synthesis of Alanine, Aspartate Nonessential amino acids such as alanine and aspartate are produced by transamination. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Synthesis of Glutamine The synthesis of the other nonessential amino acids may require several reactions in addition to transamination. Glutamine is synthesized when a second amino group is added to glutamate using the energy from the hydrolysis of ATP General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Synthesis of Tyrosine Tyrosine, an aromatic amino acid with a hydroxyl group, is formed from phenylalanine, an essential amino acid, and oxygen. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Overview, Metabolism Catabolic pathways • degrade large molecules. • form small molecules that enter the citric acid cycle and electron transport to produce energy. Anabolic pathways • use small molecules and energy. • synthesize larger molecules in the cell. In the overall view of metabolism, there are several branch points from which compounds may be degraded for energy or used to synthesize larger molecules. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Overview, Metabolism Core Chemistry Skill Distinguishing Anabolic and Catabolic Pathways General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Match each of the following amino acids with the intermediate needed for its synthesis: 1) alanine 2) glutamate 3) aspartate A. pyruvate B. oxaloacetate C. α-ketoglutarate General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Match each of the following amino acids with the intermediate needed for its synthesis: 1) alanine 2) glutamate 3) aspartate A. pyruvate 1) alanine B. oxaloacetate 3) aspartate C. α-ketoglutarate 2) glutamate General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Phenylketonuria (PKU) In phenylketonuria (PKU), • the gene that converts phenylalanine to tyrosine is defective. • phenylalanine forms phenylpyruvate (transamination), which goes to phenylacetate (decarboxylation). • high levels of phenylacetate cause severe mental retardation. • a diet low in phenylalanine and high in tyrosine is recommended. • sweeteners and soft drinks containing aspartame, which contains phenylalanine as one of the two amino acids in its structure, should be avoided. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Phenylketonuria (PKU) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Concept Map General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.