The major source of NADPH for fatty acid synthesis
**Question:** The major source of NADPH for fatty acid synthesis
**Core Concept:** Fatty acid synthesis is a process that involves the conversion of acetyl-CoA to palmitate, a saturated fatty acid. NADPH is an essential cofactor in this process, providing reducing equivalents to the enzyme system responsible for synthesizing fatty acids.
**Why the Correct Answer is Right:** NADPH is produced in the mitochondria through the pentose phosphate pathway (PPP). Among the given options, C: **Glucose-6-phosphate dehydrogenase pathway in the pentose phosphate pathway** is the correct source of NADPH for fatty acid synthesis. In this pathway, glucose-6-phosphate is converted to 6-phosphogluconate, which then enters the oxidative phase, generating NADPH.
**Why Each Wrong Option is Incorrect:**
A: **Oxidative branch of the PPP** - This branch generates NADH, not NADPH, thus not relevant to fatty acid synthesis.
B: **NADPH generation in the citric acid cycle** - While the citric acid cycle generates NADPH, it is not the major source for fatty acid synthesis.
D: **NADPH generation in the electron transport chain** - The electron transport chain generates NADH, not NADPH, making this option incorrect as well.
**Why Option C is Right:**
**Clinical Pearl:** The oxidative branch of the PPP is crucial for maintaining the redox balance in cells and contributes to the production of nucleotides and ribose-5-phosphate, essential for DNA and RNA synthesis, respectively.
**Correct Answer:** Oxidative branch of the pentose phosphate pathway (PPP) - In the oxidative phase, glucose-6-phosphate is converted to 6-phosphogluconate, which generates NADPH. This NADPH is essential for the synthesis of fatty acids in the mitochondria. The other options are incorrect because they refer to NADH production, which is not involved in fatty acid synthesis.