The major source of NADPH for fatty acidsynthesis ?
**Core Concept**
The major source of NADPH for fatty acid synthesis is a critical aspect of lipid metabolism. Fatty acid synthesis involves the reduction of acetyl-CoA to form fatty acids, which requires a reducing agent. NADPH is the primary electron donor in this process.
**Why the Correct Answer is Right**
NADPH is generated in the pentose phosphate pathway, specifically through the oxidative phase. This pathway is activated in response to increased glucose availability. The enzyme glucose-6-phosphate dehydrogenase (G6PDH) catalyzes the first step of the pentose phosphate pathway, converting glucose-6-phosphate into 6-phosphogluconolactone, generating NADPH in the process. The NADPH produced in this pathway is then used for fatty acid synthesis, as well as other anabolic reactions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the source of NADPH for fatty acid synthesis. Glycolysis is a different metabolic pathway that does not generate NADPH.
**Option B:** The citric acid cycle is involved in oxidative metabolism, not the generation of NADPH for fatty acid synthesis.
**Option C:** This option is incorrect because the major source of NADPH for fatty acid synthesis is not the cytosolic NADH.
**Clinical Pearl / High-Yield Fact**
The pentose phosphate pathway is activated in response to increased glucose availability, making it an important regulator of NADPH generation for fatty acid synthesis.
**Correct Answer:** C.