Amino acids are primarily required for protein synthesis. In D. melanogaster, of the 20 standard amino acids, 10 are essential and must be acquired through the diet (L-histidine, L-lysine, L-phenylalanine, L-methionine, L-isoleucine, L-leucine, L-valine, L-threonine, L-tryptophan, and L-arginine), while the remaining 10 can be synthesized endogenously either in the cytosol or the mitochondrion. Non-essential amino acids are produced using either TCA cycle or glycolysis metabolic intermediates (L-alanine, L-aspartate, L-glutamate, L-serine) or by modification of other amino acids (L-asparagine, L-cysteine, L-glutamine, glycine, L-proline, and L-tyrosine). Beyond their role in protein synthesis, amino acid catabolism to pyruvate and acetyl-CoA can be used for producing glucose, ATP and fatty acids. In addition, some amino acids function also as precursors for the biosynthesis of neurotransmitters, antioxidants, nucleotides, heme, and signaling molecules. (Adapted from PMID:33795250.)