Which intermediate in the citric acid cycle is crucial for the biosynthesis of fatty acids?

Citrate is a critical intermediate in the citric acid cycle that plays an essential role in the biosynthesis of fatty acids. When energy levels in the cell are high, citrate accumulates and can be exported from the mitochondria into the cytosol. In the cytosol, citrate is converted back into acetyl-CoA and oxaloacetate. The acetyl-CoA generated is a key substrate for fatty acid synthesis; it serves as the building block for the elongation of fatty acid chains in the cytosolic fatty acid synthesis pathway.

The conversion of citrate to acetyl-CoA is facilitated by the enzyme ATP-citrate lyase, highlighting the importance of citrate as a link between the energy-producing pathways in the mitochondria and the biosynthetic processes occurring in the cytosol. The presence of high levels of citrate promotes lipogenesis, allowing the cell to convert excess energy into fatty acids for storage or cellular membrane production.

In contrast, the other intermediates listed, such as succinate, malate, and alpha-ketoglutarate, play less direct roles in fatty acid biosynthesis. They are primarily involved in energy production and various metabolic pathways rather than serving as direct precursors for lipid synthesis.