The important intermediate product of biosynthesis of fatty acid is
**Core Concept**
The biosynthesis of fatty acids occurs in the cytoplasm and involves a series of enzyme-catalyzed reactions, ultimately producing a long-chain fatty acid. This process starts with the conversion of acetyl-CoA into a key intermediate, which then undergoes a series of elongation and desaturation reactions to produce the final product.
**Why the Correct Answer is Right**
The correct answer is Acetyl-CoA Carboxylase (ACC) intermediate, malonyl-CoA. Malonyl-CoA is a critical intermediate in the biosynthesis of fatty acids. It is formed by the carboxylation of acetyl-CoA by the enzyme acetyl-CoA carboxylase (ACC). This reaction is the committed and most heavily regulated step in fatty acid synthesis. Malonyl-CoA then serves as the primary building block for the elongation of fatty acids, which involves the sequential addition of two-carbon units to the growing fatty acid chain.
**Why Each Wrong Option is Incorrect**
**Option A:** Acetoacetyl-CoA is a key intermediate in the biosynthesis of cholesterol and other steroids, but not in the biosynthesis of fatty acids.
**Option B:** HMG-CoA (3-Hydroxy-3-methylglutaryl-CoA) is a key intermediate in the biosynthesis of cholesterol, but not in the biosynthesis of fatty acids.
**Option C:** Oleoyl-CoA is a long-chain fatty acyl-CoA, but it is not an intermediate in the biosynthesis of fatty acids, rather it is a product of fatty acid elongation.
**Clinical Pearl / High-Yield Fact**
Malonyl-CoA has a significant role in regulating fatty acid oxidation, as it inhibits carnitine palmitoyltransferase 1 (CPT1), a key enzyme in the transport of fatty acids into the mitochondria for beta-oxidation.
**Correct Answer: C. Malonyl-CoA**