Metabolic Marshall Law: The Mandatory Urea Cycle

The provided source explains that **amino acids** are distinct from other nutrients because they contain **nitrogen** and cannot be **stored for future use** by the body. While these molecules primarily function as building blocks for **cellular proteins** and essential compounds like **neurotransmitters**, any surplus is immediately broken down for **energy production**. A critical byproduct of this metabolic process is **ammonia**, a toxic substance that the body must neutralize through the **urea cycle**. This ensures that the **carbon skeletons** of excess amino acids are safely repurposed for fuel while harmful nitrogenous waste is eliminated. Ultimately, the text highlights the unique chemical pathways required to manage **protein metabolism** compared to the storage of fats or sugars.