Now, this also takes place outside the liver, but ultimately all the ammonium ends up inside the liver, inside the matrix of that mitochondria. And so the extra ammonium basically is used. It's combined with carbon dioxide that comes from bicarbonate, as we'll see in just a moment. And using two ATP molecules, we form a high energy molecule, a molecule that has a high transfer potential known as carbon oil phosphate. Now, this takes place in the matrix of the mitochondria. We have an amino acid called ornithine that actually formed in step five of the urea cycle that moves into the matrix of the mitochondria.