Some amino acids can actually enter as intermediates of the citric acid cycle. And the citric acid cycle has other important functions as well. It also actually gives us those intermediate molecules, the building block molecules such as oxalo acetate molecules that we use to form many building blocks. So things like nitrogenous, nucleotide bases, amino acids, glucose molecules. Because we have the oxalo acetate in the citric acid cycle that we can use to form glucose via gluconeogenesis, we also form things like porphyrin molecules. Remember that porphyrin is the organic carbon based component of heme groups used by things like hemoglobin proteins and my global protein.