Which of the following occurs during carbohydrate metabolism?

The process of carbohydrate metabolism is primarily defined by the breakdown of carbohydrates to generate energy, and it involves several key biochemical pathways. Glycolysis is the first step in this process, where glucose is converted into pyruvate while generating ATP and NADH. Following glycolysis, if oxygen is available, pyruvate enters the citric acid cycle (also known as the Krebs cycle), where it undergoes further transformations to produce additional ATP and electron carriers like NADH and FADH2.

These electron carriers then participate in the electron transport system (ETS), where they facilitate the production of a significant amount of ATP through oxidative phosphorylation. This pathway is crucial as it efficiently converts the energy stored in carbohydrates into a usable form (ATP) for the cell.

The other options do not accurately represent the primary functions associated with carbohydrate metabolism. For instance, while protein synthesis and oxidation of amino acids involve other metabolic pathways, they do not directly relate to carbohydrate breakdown. Similarly, fatty acid oxidation pertains to lipid metabolism, distinct from the processes involved in directly metabolizing carbohydrates. Therefore, the correct answer encompasses the full sequence of reactions necessary for efficiently converting carbohydrates into energy.