Final answer:
The nitrogen-containing amino group from amino acids is removed by deamination, resulting in ammonia. The liver converts ammonia into urea, which is then excreted. The carbon skeletons can be converted to glucose or ketones or enter the citric acid cycle.
Step-by-step explanation:
When amino acids are not required for synthesizing new proteins, their excess and fate during starvation are important for energy metabolism. The amino group of these amino acids, which is the nitrogen-containing part, is removed predominantly through a process called deamination. This conversion results in ammonia, which is toxic to the body in high concentrations. In response, the liver efficiently converts ammonia into a less toxic compound called urea through the urea cycle. Urea is then excreted from the body via urine. Additionally, the carbon skeletons that remain after the removal of the amino group can either be transformed into glucose or ketones or enter the citric acid cycle as metabolic intermediates, depending on the body's energy needs.
If the body is in a state of energy deficit, such as fasting or starvation, the deaminated carbon skeletons can serve as a substrate for glucose production, a process known as gluconeogenesis. Overall, the conservation of nitrogen from amino acids is crucial, and the metabolic pathways involved are essential for maintaining the balance between energy production and the safe excretion of nitrogenous waste.