Which molecule provides the most energy when completely oxidized?

Lipids provide the most energy when completely oxidized due to their chemical structure and composition. Lipids, which include fats and oils, are primarily composed of long chains of fatty acids. These fatty acids have a highly reduced state, meaning they contain a higher number of electrons that can be transferred to electron carriers during cellular respiration.

When lipids undergo oxidation, they break down through a process called beta-oxidation. This process ultimately leads to the production of acetyl-CoA, which enters the citric acid cycle (Krebs cycle) and subsequently generates a large number of ATP molecules through oxidative phosphorylation. In fact, the energy yield from the complete oxidation of lipids is significantly higher compared to carbohydrates and proteins. For instance, one molecule of palmitic acid, a common fatty acid, can yield about 106 ATP molecules when fully oxidized.

While carbohydrates and proteins can also provide energy, they do not match the caloric yield of lipids. Carbohydrates, such as glucose, provide approximately 36 ATP molecules upon complete oxidation, while proteins yield energy variably based on their amino acid composition but still fall short of the energy produced from lipids. Nucleic acids, while vital for storing genetic information, are not primarily