How are amino acids primarily used for energy?

Amino acids can serve as an energy source, but their usage primarily involves the process of deaminating the amino group. This involves removing the amino group from the amino acid, which leaves behind a carbon skeleton. This carbon skeleton can then enter various metabolic pathways, including the Krebs cycle (or citric acid cycle), where it can be fully oxidized to produce energy.

When the amino group is removed, the body can convert the remaining carbon skeleton into glucose, ketone bodies, or directly into intermediates that can enter the Krebs cycle, providing a means for energy production. This process begins when the liver takes up amino acids and removes the amino group, allowing the body to not only recycle nitrogen for other amino acids but also effectively utilize the remaining components for energy generation and metabolism.

Thus, the correct answer identifies the crucial first step of amino acid catabolism that leads to their use as an energy source, clarifying how the amino group is separated from the carbon component before the carbons are funneled into energy-producing pathways.