When is ATP released?

When is ATP released?

• A. During the breakdown of glucose, fatty acids, and amino acids
• B. During photosynthesis
• C. During digestion of proteins
• D. In the presence of oxygen only

Answer: (A)

Energy is released when nutrients are broken down in cellular respiration. Glucose, fatty acids, and amino acids are all catabolized through pathways that transfer energy to ATP. Carbohydrates start with glycolysis, which makes a small amount of ATP and NADH; the resulting pyruvate then enters the mitochondria, where the citric acid cycle and oxidative phosphorylation produce most of the ATP. Fats enter energy production through beta-oxidation, which creates acetyl-CoA and plenty of NADH and FADH2 to power the electron transport chain. Amino acids can be converted into intermediates that feed into these same pathways and ultimately yield ATP after deamination and entry into metabolism. This is why ATP release is tied to the breakdown of these macronutrients. The idea that ATP is released only in the presence of oxygen isn’t accurate, because glycolysis can generate ATP without oxygen (though less efficiently). Photosynthesis uses energy to build glucose and stores it rather than releasing ATP. Digestion itself involves breaking down proteins, but ATP release comes from the subsequent metabolic processing of the resulting amino acids.

Energy is released when nutrients are broken down in cellular respiration. Glucose, fatty acids, and amino acids are all catabolized through pathways that transfer energy to ATP. Carbohydrates start with glycolysis, which makes a small amount of ATP and NADH; the resulting pyruvate then enters the mitochondria, where the citric acid cycle and oxidative phosphorylation produce most of the ATP. Fats enter energy production through beta-oxidation, which creates acetyl-CoA and plenty of NADH and FADH2 to power the electron transport chain. Amino acids can be converted into intermediates that feed into these same pathways and ultimately yield ATP after deamination and entry into metabolism.

This is why ATP release is tied to the breakdown of these macronutrients. The idea that ATP is released only in the presence of oxygen isn’t accurate, because glycolysis can generate ATP without oxygen (though less efficiently). Photosynthesis uses energy to build glucose and stores it rather than releasing ATP. Digestion itself involves breaking down proteins, but ATP release comes from the subsequent metabolic processing of the resulting amino acids.