In synthesis of fatty acids, energy is supplied by:
**Core Concept**
The synthesis of fatty acids involves a complex biochemical pathway that requires energy to initiate and sustain the process. This energy is derived from the reduction of acetyl-CoA molecules to produce the fatty acid chain.
**Why the Correct Answer is Right**
The correct answer is **NADPH** (Nicotinamide adenine dinucleotide phosphate). NADPH is a high-energy electron carrier that plays a crucial role in the synthesis of fatty acids. In the citric acid cycle and fatty acid synthesis, NADPH is generated in the pentose phosphate pathway, which provides the necessary reducing power for the reduction of acetyl-CoA molecules to produce the fatty acid chain. This process is initiated by acetyl-CoA carboxylase, which converts acetyl-CoA into malonyl-CoA, and then fatty acid synthase, which uses NADPH to reduce the growing fatty acid chain.
**Why Each Wrong Option is Incorrect**
**Option A:** **ATP** is incorrect because while ATP is required for the initiation of fatty acid synthesis, it is not the primary energy source for the reduction of acetyl-CoA molecules. ATP is used to activate acetyl-CoA and other substrates, but NADPH is the key energy source for the synthesis of fatty acids.
**Option B:** **FADH2** is incorrect because FADH2 is a coenzyme involved in the electron transport chain and is not directly involved in the synthesis of fatty acids.
**Option C:** **GTP** is incorrect because GTP is involved in protein synthesis and signal transduction, but it is not directly involved in the synthesis of fatty acids.
**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that patients with diabetes mellitus often have elevated levels of fatty acids in their blood due to increased lipolysis and decreased insulin-mediated inhibition of fatty acid synthesis.
**Correct Answer: C. NADPH. NADPH**