This source explains that unlike other nutrients, amino acids contain nitrogen, which poses a unique challenge during metabolic breakdown. Because the body cannot store surplus amino acids as it does with fats or sugars, it must either use them for protein synthesis or dismantle them for energy. When these molecules are broken down, the nitrogen is converted into ammonia, a toxic byproduct that requires the urea cycle for safe elimination. The remaining carbon skeletons are repurposed for energy production or transformed into vital molecules like neurotransmitters and nucleotides. Ultimately, the text highlights the specialized pathways the body uses to manage these essential compounds while preventing toxic buildup.

Acetyl-CoA is a high-energy molecule derived from all nutrients including: carbohydrates, lipids, proteins, ketone bodies and alcohol. By breaking its thioester bond within the TCA cycle, it generates electron carriers and GTP, yielding approximately 12 ATP per molecule to power cellular processes.

The brain's panic button is a precipitous drop in plasma glucose. Its response through the hypothalamus initiates the release of glucagon, epinephrine and cortisol from the pancreas and adrenal glands, respectively. The outcome of these hormones is to instruct the liver through their respective receptors to increase its output of glucose, thus restoring it to its normal levels.