Metabolic pool

The catabolic pathways involved in the glycolysis and the Krebs cycle constitute the metabolic pool that supplies building blocks for other anabolic reactions in the cell. An excess of carbohydrates can result in an accumulation of Acetyl-CoA molecules. If there is a great excess of Acetyl-CoA, the acetyl groups can be committed to fatty acid synthesis for long-term energy storage. Glycolytic products can also be the starting point for amino acid synthesis. 3-phosphoglycerate can be used to synthesize glycine, cysteine and serine. Pyruvate can be used to generate alanine, valine and leucine. Oxaloacetate from the Krebs cycle can be used as a starting point for aspartate, lysine, asparagine, methionine, threonine and isoleucine. Glutamate and glutamine are synthesized from α-ketoglutarate formed during the Krebs cycle. While most of the 20 amino acids can be synthesized de novo, there are 9 essential amino acids in humans that can not be synthesized in sufficient quantity and therefore must be gained from the diet. These essential amino acids include: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.