The human body requires 20 amino acids to function properly, and these amino acids are classified into two categories: essential and non-essential amino acids. Essential amino acids cannot be synthesized by the body and must be obtained through the diet, while non-essential amino acids can be synthesized by the body from other molecules.Essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Non-essential amino acids include alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.Non-essential amino acid synthesis:1. Alanine: Synthesized from pyruvate through the action of alanine aminotransferase, which transfers an amino group from glutamate to pyruvate.2. Asparagine: Synthesized from aspartate and glutamine through the action of asparagine synthetase.3. Aspartic acid: Synthesized from oxaloacetate through the action of aspartate aminotransferase, which transfers an amino group from glutamate to oxaloacetate.4. Cysteine: Synthesized from serine and homocysteine through the action of cystathionine beta-synthase and cystathionine gamma-lyase.5. Glutamic acid: Synthesized from alpha-ketoglutarate through the action of glutamate dehydrogenase or aminotransferases.6. Glutamine: Synthesized from glutamate and ammonia through the action of glutamine synthetase.7. Glycine: Synthesized from serine through the action of serine hydroxymethyltransferase.8. Proline: Synthesized from glutamate through the action of glutamate 5-kinase and glutamate 5-semialdehyde dehydrogenase.9. Serine: Synthesized from 3-phosphoglycerate through the action of phosphoglycerate dehydrogenase, phosphoserine aminotransferase, and phosphoserine phosphatase.10. Tyrosine: Synthesized from phenylalanine through the action of phenylalanine hydroxylase.Essential amino acids must be obtained through the diet, but their metabolism and catabolism also involve various biochemical pathways:1. Histidine: Metabolized to urocanic acid and glutamate through the action of histidine ammonia-lyase and urocanase.2. Isoleucine: Catabolized through the branched-chain alpha-keto acid dehydrogenase complex, producing acetyl-CoA and propionyl-CoA.3. Leucine: Catabolized through the branched-chain alpha-keto acid dehydrogenase complex, producing acetyl-CoA and acetoacetate.4. Lysine: Metabolized to acetyl-CoA and acetoacetyl-CoA through the action of lysine-ketoglutarate reductase and saccharopine dehydrogenase.5. Methionine: Converted to S-adenosylmethionine SAM through the action of methionine adenosyltransferase, and further metabolized to homocysteine and cysteine.6. Phenylalanine: Converted to tyrosine through the action of phenylalanine hydroxylase, and further metabolized to fumarate and acetoacetate.7. Threonine: Metabolized to alpha-ketobutyrate and glycine through the action of threonine dehydratase and serine hydroxymethyltransferase.8. Tryptophan: Metabolized to kynurenine and further to acetyl-CoA and alanine through the action of tryptophan 2,3-dioxygenase and kynureninase.9. Valine: Catabolized through the branched-chain alpha-keto acid dehydrogenase complex, producing propionyl-CoA and isobutyryl-CoA.These pathways are interconnected with the central metabolic pathways, such as glycolysis, the citric acid cycle, and the urea cycle, allowing the body to maintain amino acid homeostasis and produce energy from amino acid catabolism.