Question

Which of the following molecules will produce the most ATP per mole? a. glucose or maltose b. myristic acid, \(\mathrm{CH}_{3}-\left(\mathrm{CH}_{2}\right)_{12}-\mathrm{COOH}\), or stearic acid, \(\mathrm{CH}_{3}-\left(\mathrm{CH}_{2}\right)_{16}-\mathrm{COOH}\) c. glucose or two acetyl CoAs d. glucose or caprylic acid (C \(_{8}\) ) e. citrate or succinate in one turn of the citric acid cycle

Short answer

a. maltoseb. stearic acidc. samed. caprylic acide. citrate

Step-by-step solution

Determine the Primary Energy Source in Each Pair

Each molecule or pair represents a different source of potential energy that the cell can use to produce ATP. The goal is to identify which molecule in each pair yields more ATP.

Compare Glucose and Maltose

Glucose is a single sugar molecule, while maltose consists of two glucose molecules. Therefore, the breakdown of maltose produces twice as much ATP as the breakdown of glucose alone. Maltose will yield more ATP.

Compare Myristic Acid and Stearic Acid

Myristic acid has 14 carbons (\(\text{CH}_3-(\text{CH}_2)_{12}-\text{COOH}\)), while stearic acid has 18 carbons (\(\text{CH}_3-(\text{CH}_2)_{16}-\text{COOH}\)). Longer fatty acids provide more ATP because each cycle of beta-oxidation yields ATP. Stearic acid will yield more ATP.

Compare Glucose and Two Acetyl CoAs

Glucose breaks down into two molecules of pyruvate, which then become acetyl CoA. So, one molecule of glucose produces two acetyl CoA. Therefore, ATP yield from glucose and two acetyl CoA is the same.

Compare Glucose and Caprylic Acid (C8)

Caprylic acid is a fatty acid with 8 carbons. Each cycle of beta-oxidation for fatty acids also yields ATP, potentially producing more ATP than glucose. Caprylic acid will yield more ATP.

Compare Citrate and Succinate in the Citric Acid Cycle

In one turn of the citric acid cycle, citrate yields more ATP than succinate because it results in a higher number of electron carriers (NADH and FADH2) being produced. Thus, citrate will yield more ATP.

Key concepts

glucose metabolism

Glucose metabolism is a fundamental process for generating energy in cells. It starts with glycolysis, where one molecule of glucose (C\(_6\)H\(_{12}\)O\(_6\)) is broken down into two molecules of pyruvate in the cytoplasm. This process yields 2 ATP and 2 NADH. The pyruvate is then transported into the mitochondria, where it is converted into acetyl CoA before entering the citric acid cycle.

beta-oxidation

Beta-oxidation is the process of breaking down fatty acids into acetyl CoA units in the mitochondria. Each round of beta-oxidation shortens the fatty acid chain by two carbon atoms and produces one molecule each of NADH and FADH\(_2\), in addition to acetyl CoA. Longer fatty acids like stearic acid (18-carbons) yield more ATP than shorter ones like myristic acid (14-carbons), because they undergo more rounds of beta-oxidation, producing more electron carriers.

citric acid cycle

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a series of chemical reactions used by aerobic organisms to generate energy. Each acetyl CoA that enters the cycle combines with oxaloacetate to form citrate, which goes through several transformations. Throughout the cycle, ATP (or GTP), NADH, and FADH\(_2\) are produced. These electron carriers then enter the electron transport chain to produce additional ATP. Citrate generates higher energy yields earlier in the cycle compared to succinate.

acetyl CoA

Acetyl CoA is a crucial molecule in metabolism, acting as a link between glycolysis and the citric acid cycle. It is formed by the oxidative decarboxylation of pyruvate in the mitochondria. Acetyl CoA is also produced through beta-oxidation of fatty acids. This molecule feeds into the citric acid cycle, leading to the production of electron carriers NADH and FADH\(_2\), which drive ATP production in the electron transport chain.