1. Biosynthesis of the nutritionally nonessential amino acids

2. Biosynthesis of the nutritionally nonessential amino acids
Amino acid deficiency states can result if nutritionally essential amino acids are absent from the diet, or are present in inadequate amounts.
Amino acid deficiency states, while comparatively rare in the Western world, are endemic in certain regions of West Africa where diets rely heavily on grains that are poor sources of tryptophan and lysine.

3. These nutritional disorders include:
kwashiorkor, which results when a child is weaned onto a starchy diet poor in protein.
marasmus, in which both caloric intake and specific amino acids are deficient.
Patients with short bowel syndrome unable to absorb sufficient quantities of calories and nutrients suffer from significant nutritional and metabolic abnormalities.
a dietary deficiency of vitamin C is associated with an impaired ability of connective tissue to form hydroxyproline and hydroxylysine. The resulting conformational instability of collagen results in bleeding gums, swelling joints, poor wound healing, and ultimately in death.

4. Menkes' syndrome, characterized by kinky hair and growth retardation, results from a dietary deficiency of copper, which is an essential cofactor for lysyl oxidase.
Ehlers-Danlos syndrome, a group of connective tissue disorders that result in mobile joints and skin abnormalities due to defects in the genes that encode enzymes lysyl hydroxylase.
Nutritionally essential & nutritionally non essential amino acids The terms "essential" and "nonessential" are misleading since all 20 common amino acids are essential to ensure health.

6. Glutamate Dehydrogenase, Glutamine Synthetase, Amino transferases Play Central Roles in Amino Acid Biosynthesis
A. Synthesis from α-keto acids
Alanine, aspartate, and Glutamate are synthesized by transfer of an amino group to the α-keto acids pyruvate, oxaloacetate, and α-keto-glutarate, respectively. Glutamate is unusual in that it can also be synthesized by reductive amidation of α-ketoglutarate catalyzed by glutamate dehydrogenase

7. B. Synthesis by amidation
1. Glutamine: This amino acid, which contains an amide linkage with ammonia at the γ-carboxyl, is formed from glutamate by glutamine synthetase The reaction is driven by the hydrolysis of ATP.
This reaction also serves as a major mechanism for the detoxification of ammonia in brain and liver .
2. Asparagine: This amino acid, which contains an amide linkage with ammonia at the β-carboxyl, is formed from aspartate by asparagine synthetase, using glutamine as the amide donor rather than ammonium ion. The reaction requires ATP.
Figure 27–2 the glutamine synthetase reaction

8. C. Proline
Glutamate is converted to proline by cyclization and reduction reactions.
Biosynthesis of proline similar to those of proline catabolism, but in which glutamate -phosphate is an intermediate.
D. Glycine, Serine, and Cysteine
Glycine: Glycine aminotransferases can catalyze the synthesis of glycine from glyoxylate and glutamate or alanine. Additional important mammalian routes for glycine formation are from choline and from serine ( serine hydroxymethyl transferase) reaction. (H4 folate,tetrahydrofolate.)

9. Serine
Oxidation of the -hydroxyl group of the glycolytic intermediate 3-phosphoglycerate by 3-phosphoglycerate dehydrogenase converts it to 3-phosphohydroxypyruvate. Transamination and subsequent dephosphorylation then forms serine .

10. Cysteine
While not nutritionally essential, cysteine is formed from methionine, which is nutritionally essential. Following conversion of methionine to homocysteine , homocysteine and serine form cystathionine, whose hydrolysis forms cysteine and homoserine.
Figure 27–9 Conversion of homocysteine and serine to homoserine and cysteine. The sulfur of cysteine derives from methionine and the carbon skeleton from serine.

11. E. Tyrosine
Tyrosine is formed from phenylalanine by phenylalanine hydroxylase.
The reaction requires molecular oxygen and the coenzyme tetrahydrobiopterin.
One atom of molecular oxygen becomes the hydroxyl group of tyrosine, and the other atom is reduced to water.
During the reaction, tetrahydrobiopterin is oxidized to dihydrobiopterin.
Tetrahydrobiopterin is regenerated from dihydrobiopterin in a separate reaction requiring NADPH.

12. Hydroxyproline & Hydroxylysine
Hydroxyproline and hydroxylysine occur principally in collagen. Since there is no tRNA for either hydroxylated amino acid. Peptidyl hydroxyproline and hydroxylysine arise from proline and lysine catalyzed by prolyl hydroxylase and lysyl hydroxylase of skin, skeletal muscle, and granulating wounds.
But only after these amino acids have been incorporated into peptides.
Requires: substrate, molecular O2, ascorbate, Fe2+, and α -ketoglutarate . One atom of O2 is incorporated into proline or lysine, the other into succinate. A deficiency of the vitamin C required for these hydroxylases results in Scurvy.

13. Selenocysteine, the 21st Amino Acid
While its occurrence in proteins is uncommon, selenocysteine is present at the active site of several human enzymes that catalyze redox reactions. Examples include glutathione peroxidase and the deiodinase that converts thyroxine to triiodothyronine.
replacement of selenocysteine by cysteine can significantly decrease catalytic activity.
Impairments in human selenoproteins have been implicated in tumorigenesis and atherosclerosis, and are associated with selenium deficiency cardiomyopathy .
Unlike hydroxyproline or hydroxylysine, selenocysteine arises co-translationally during its incorporation into peptides.
Biosynthesis requires cysteine, selenate (SeO4-2), ATP, a specific tRNA, and several enzymes. Serine provides the carbon skeleton of selenocysteine.

14. METABOLIC DEFECTS IN AMINO ACID METABOLISM
Incidence of inherited disease of amino acid metabolism[cystinuria is the most common genetic error of amino acid transport