Nitrogen, Nitrogen Cycle and Excretion of Nitrogen

In the lectures on amino acid metabolism, I've talked about how amines are moved from one molecule to another, and how ammonia is a toxic byproduct of their metabolism. With this lecture, I'll talk about how those amines and how that ammonia are combined and prepared for excretion. Nitrogen in the body, as we have seen, comes in various forms. Balance is absolutely critical. Nitrogen is an essential nutrient, but it’s also one that two high levels can be toxic. The body must be able to handle the nitrogen arising from amino acid metabolism. But nitrogen is also needed for the synthesis of other molecules. This includes the nucleotides, ATP, GTP, CTP, UTP, dATP, dCTP, dGTP and dTTP. Nitrogen is also needed for making of non-protein amino acids. These include ornithine, citrulline and sarcosine as shown in the screen. And there are yet other nitrogen containing compounds that are necessary for synthesis in the body. This includes choline, various vitamins and carnitine. Now, the nitrogen cycle is a very important cycle in our environment. Nitrogen is a -- the nitrogen in our atmosphere must be reduced. And there are nitrifying organisms at the very deepest parts of our soil that grab that nitrogen and convert it into the amines that are useful for higher organisms. That over all process is shown on the slide. Now, nitrogen must be excreted if the balance is to be properly maintained. As I've noted, amino acids through transamination make nitrogen mobile. It's very easy to move nitrogen from one amino acid to a keto acid and vice versa. The toxicity of ammonia means that the nitrogen that's produced as a byproduct of amino acid metabolism must be handled properly. In the excretion process, there are various strategies that are employed by different organisms. Organisms...