Why are fats metabolized after carbohydrates?

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Multiple Choice

Why are fats metabolized after carbohydrates?

Fats are energy-rich but hydrophobic, so they aren’t water-soluble and don’t mix with the aqueous cellular environment as readily as carbohydrates. To be used for energy, fats must first be broken down by lipases (lipolysis) to release fatty acids, then those fatty acids are activated to acyl-CoA, transported into mitochondria by the carnitine shuttle, and finally cleaved by beta-oxidation into acetyl-CoA along with NADH and FADH2. The acetyl-CoA then feeds the citric acid cycle and oxidative phosphorylation to produce ATP. This multi-step processing makes fat metabolism slower and more resource-intensive, so fats are metabolized after carbohydrates when both are available. Carbohydrates, by contrast, can enter glycolysis directly with fewer prerequisites, which is why they’re used first.

Fats are energy-rich but hydrophobic, so they aren’t water-soluble and don’t mix with the aqueous cellular environment as readily as carbohydrates. To be used for energy, fats must first be broken down by lipases (lipolysis) to release fatty acids, then those fatty acids are activated to acyl-CoA, transported into mitochondria by the carnitine shuttle, and finally cleaved by beta-oxidation into acetyl-CoA along with NADH and FADH2. The acetyl-CoA then feeds the citric acid cycle and oxidative phosphorylation to produce ATP. This multi-step processing makes fat metabolism slower and more resource-intensive, so fats are metabolized after carbohydrates when both are available. Carbohydrates, by contrast, can enter glycolysis directly with fewer prerequisites, which is why they’re used first.

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