Fates of the Carbon Atoms from Amino Acids Synthesis of Amino Acids Chapter 25 Metabolic Pathways for Lipids and Amino Acids

2 Carbon Atoms from Amino Acids Carbon skeletons of amino acids are intermediates or converted to intermediates for use in the citric acid cycle. Three-carbon skeletons: Alanine, serine, and cysteine Pyruvate Four-carbon skeletons: Aspartate, asparagine Oxaloacetate Five-carbon skeletons: Glutamine, glutamate, proline, arginine, histidine Glutamate

3 Three carbon skeletons

4 Four carbon skeletons

5 Five-carbon skeletons

6 Glucogenic and Ketogenic Amino Acids Amino acids are classified as: Glucogenic if they generate pyruvate or oxaloacete, which can be used to synthesize glucose. Ketogenic if they generate acetoacetyl CoA or acetyl CoA, which can form ketone bodies or fatty acids.

7 Ketogenic Glucogenic

8 Sources of Amino Acids Essential amino acids must be obtained in the diet. Nonessential amino acids are synthesized in the body.

9 Synthesis of Amino Acids In humans, transamination of compounds from glycolysis or the citric acid cycle produces nonessential amino acids.

10 Synthesis of Glutamine Glutamine is synthesized by adding another amino group to glutamate. NH 3 + Glutamine | synthetase - OOC—CH—CH 2 —CH 2 —COO - + NH 3 + ATP Glutamate NH 3 + O | || - OOC—CH—CH 2 —CH 2 —C—NH 2 + ADP + P i Glutamine

11 Phenylketonurea (PKU) In phenylketonurea (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.

12 Phenylketonurea (PKU)

13 Overview of Metabolism In metabolism: Catabolic pathways degrade large molecules. Anabolic pathway synthesize molecules. Branch points determine which compounds are degraded to acetyl CoA to meet energy needs or converted to glycogen for storage.

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