Which of the following molecules will produce the most ATP per mole?
d. lauric acid (C₁₂₎ or palmitic acid (C₁₆)

Verified step by step guidance

Step 1: Understand the relationship between the number of carbon atoms in a fatty acid and ATP production. Fatty acids with more carbon atoms undergo more rounds of beta-oxidation, producing more acetyl-CoA molecules, which enter the citric acid cycle to generate ATP.

Step 2: Compare the molecular formulas of lauric acid (C₁₂) and palmitic acid (C₁₆). Lauric acid has 12 carbon atoms, while palmitic acid has 16 carbon atoms.

Step 3: Recall that each round of beta-oxidation removes two carbon atoms from the fatty acid chain, producing one acetyl-CoA molecule. A longer fatty acid chain (like palmitic acid) will undergo more rounds of beta-oxidation compared to a shorter chain (like lauric acid).

Step 4: Consider the additional ATP generated during the citric acid cycle and oxidative phosphorylation for each acetyl-CoA molecule produced. Since palmitic acid produces more acetyl-CoA molecules, it will ultimately generate more ATP per mole.

Step 5: Conclude that palmitic acid (C₁₆) will produce more ATP per mole than lauric acid (C₁₂) due to its longer carbon chain and greater number of beta-oxidation cycles.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Fatty Acid Oxidation

Fatty acid oxidation is the metabolic process by which fatty acids are broken down in the mitochondria to produce energy. This process involves the conversion of fatty acids into acetyl-CoA, which then enters the citric acid cycle, leading to the production of ATP. The length of the fatty acid chain affects the amount of ATP generated, as longer chains yield more acetyl-CoA and thus more energy.

ATP Yield from Fatty Acids

The ATP yield from fatty acids is determined by the number of carbon atoms in the fatty acid chain. Each cycle of beta-oxidation produces one molecule of acetyl-CoA and generates NADH and FADH2, which are further processed in the electron transport chain to produce ATP. Generally, longer fatty acids like palmitic acid (C16) produce more ATP than shorter ones like lauric acid (C12) due to the increased number of acetyl-CoA produced.

Comparative Energy Content

Comparative energy content refers to the amount of energy stored in different molecules, which can be assessed by their structure and composition. In the case of fatty acids, the longer the carbon chain, the higher the energy content, as more carbon-hydrogen bonds are present. This concept is crucial for understanding why palmitic acid, with its longer chain, will yield more ATP compared to lauric acid.