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Ch.12 Food as Fuel An Overview of Metabolism
Frost - General, Organic and Biological Chemistry 4th Edition
Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Not the one you use?Change textbook
All textbooksFrost 4th EditionCh.12 Food as Fuel An Overview of MetabolismProblem 32
Chapter 8, Problem 32

Explain how the catabolism of fructose differs from that of glucose.

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Fructose and glucose are both monosaccharides, but they enter glycolysis through different pathways due to their structural differences. Begin by understanding that fructose is primarily metabolized in the liver, while glucose is metabolized in most cells of the body.
Fructose is phosphorylated by the enzyme fructokinase in the liver to form fructose-1-phosphate. This step bypasses the regulatory enzyme hexokinase, which is used in glucose metabolism. Hexokinase phosphorylates glucose to form glucose-6-phosphate.
Fructose-1-phosphate is then cleaved by the enzyme aldolase B into two three-carbon molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde. In contrast, glucose-6-phosphate enters glycolysis directly and is converted into fructose-6-phosphate before being split into DHAP and glyceraldehyde-3-phosphate.
Glyceraldehyde from fructose metabolism is phosphorylated by triose kinase to form glyceraldehyde-3-phosphate, which then enters the glycolysis pathway. DHAP also directly enters glycolysis. For glucose, both DHAP and glyceraldehyde-3-phosphate are produced from fructose-1,6-bisphosphate during glycolysis.
The key difference is that fructose metabolism bypasses the regulatory step controlled by phosphofructokinase-1 (PFK-1), which is a major control point in glucose metabolism. This can lead to unregulated entry of fructose into glycolysis, potentially contributing to metabolic imbalances.

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Key Concepts

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

Catabolism

Catabolism refers to the metabolic pathways that break down molecules into smaller units, releasing energy in the process. This is essential for understanding how different sugars, like fructose and glucose, are processed in the body. The energy released during catabolism is used for various cellular functions, making it a critical aspect of metabolism.
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Fructose Metabolism

Fructose metabolism primarily occurs in the liver, where fructose is phosphorylated by fructokinase to form fructose-1-phosphate. This pathway bypasses the key regulatory step of glycolysis, leading to a rapid conversion to intermediates that can enter the glycolytic pathway. This unique route can result in different metabolic effects compared to glucose, particularly in terms of energy production and fat synthesis.
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Glucose Metabolism

Glucose metabolism involves a series of well-regulated steps, primarily through glycolysis, where glucose is converted into pyruvate, producing ATP and NADH. This process is tightly controlled by various enzymes, ensuring that energy production is matched to the cell's needs. Unlike fructose, glucose metabolism is influenced by insulin, which plays a significant role in regulating blood sugar levels.
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Related Practice
Textbook Question

Name the electron carrier that transports electrons from complex I to complex III.

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Name the reaction of the citric acid cycle that reduces FAD.

Textbook Question

Name the reactions in the citric acid cycle that involve oxidative decarboxylation.

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In terms of high-energy molecules, what is the net output for one molecule of glucose undergoing glycolysis?

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The formation of lactate permits glycolysis to continue under anaerobic conditions. Explain.

Textbook Question

Name the coenzyme produced during the conversion of pyruvate to acetyl CoA.