Which of the following molecules will produce the most ATP per mole?
e. α-ketoglutarate or fumarate in one turn of the citric acid cycle

Verified step by step guidance

1. Understand the context: The citric acid cycle (also known as the Krebs cycle) is a central metabolic pathway that generates energy in the form of ATP, NADH, and FADH₂. Each intermediate in the cycle contributes differently to the production of ATP.
2. Identify the molecules in question: α-ketoglutarate and fumarate are intermediates in the citric acid cycle. α-ketoglutarate is converted to succinyl-CoA, while fumarate is converted to malate in subsequent steps of the cycle.
3. Analyze the energy yield of each molecule: The conversion of α-ketoglutarate to succinyl-CoA produces one molecule of NADH. NADH is later used in the electron transport chain to generate approximately 2.5 ATP. Additionally, the conversion of succinyl-CoA to succinate generates one molecule of GTP (equivalent to 1 ATP).
4. Compare this to fumarate: The conversion of fumarate to malate does not directly produce NADH, FADH₂, or ATP. However, the subsequent conversion of malate to oxaloacetate produces one molecule of NADH, which generates approximately 2.5 ATP in the electron transport chain.
5. Conclude: Since α-ketoglutarate produces both NADH and GTP (equivalent to ATP) in its conversion to succinyl-CoA and succinate, it yields more ATP per mole compared to fumarate, which only indirectly contributes to ATP production through NADH formation in a later step.

Key Concepts

Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle, is a key metabolic pathway that occurs in the mitochondria. It involves a series of enzymatic reactions that convert acetyl-CoA into carbon dioxide and high-energy electron carriers, such as NADH and FADH2. These carriers are crucial for ATP production in the electron transport chain, making the cycle essential for cellular respiration.

ATP Yield from Metabolites

Different metabolites yield varying amounts of ATP when oxidized. For instance, α-ketoglutarate and fumarate are intermediates in the citric acid cycle, but their ATP yield differs based on the number of high-energy electron carriers produced during their conversion. Understanding the specific ATP yield from each metabolite helps in determining which one is more efficient in energy production.

Oxidative Phosphorylation

Oxidative phosphorylation is the final stage of cellular respiration, where the energy from electron carriers (NADH and FADH2) is used to generate ATP. This process occurs in the inner mitochondrial membrane and involves the electron transport chain and ATP synthase. The efficiency of ATP production from different substrates in the citric acid cycle is ultimately linked to how effectively their electrons are transferred through this pathway.