1. 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.

2. 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.

3. Synthesis of Amino Acids
Nonessential amino acids are synthesized from intermediates of glycolysis and the citric acid cycle.

4. Synthesis of Alanine, Aspartate
Nonessential amino acids such as alanine and aspartate are produced by transamination.

5. 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

6. Synthesis of Tyrosine
Tyrosine, an aromatic amino acid with a hydroxyl group, is formed from phenylalanine, an essential amino acid, and oxygen.

7. 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.

8. Overview, Metabolism
Core Chemistry Skill Distinguishing Anabolic and Catabolic Pathways

9. 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

10. 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

11. 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.

12. Chemistry Link to Health: Phenylketonuria (PKU)

13. Concept Map