Catabolism of lipids — Fatty acids are broken down to acetyl-CoA predominantly by which metabolic pathway?

Introduction / Context:
Cells harvest energy from lipids by converting long-chain fatty acids to acetyl-CoA, which then enters the citric acid cycle and fuels oxidative phosphorylation. Correctly naming the pathway that performs this conversion is a foundational learning objective in biochemistry and metabolism.

Given Data / Assumptions:

• Fatty acids are catabolized stepwise by removing two-carbon units.
• Carbohydrate pathways (EM, ED, PPP) primarily process sugars, not fatty acids.
• Acetyl-CoA is the common product feeding the TCA cycle.

Concept / Approach:
β-oxidation repeatedly cleaves two-carbon fragments as acetyl-CoA by oxidizing the β-carbon of the acyl chain in cycles: oxidation, hydration, oxidation, and thiolysis. Entner–Doudoroff, Embden–Meyerhof (glycolysis), and the pentose phosphate pathway are carbohydrate routes that do not produce acetyl-CoA from fatty acids. Thus, β-oxidation is the correct pathway for fatty acid to acetyl-CoA conversion.

Step-by-Step Solution:

Verification / Alternative check:
Mitochondrial β-oxidation in eukaryotes and analogous processes in bacteria supply large amounts of reduced cofactors (NADH, FADH2), confirming the energy-conserving function tied to acetyl-CoA generation.

Why Other Options Are Wrong:

• Entner–Doudoroff, Embden–Meyerhof, PPP: sugar catabolism and biosynthesis routes, not fatty-acid breakdown.

Common Pitfalls:
Confusing acetyl-CoA origin from pyruvate dehydrogenase (after glycolysis) with the lipid-specific β-oxidation route.

Final Answer:
β-oxidation