Rasvasynteesiä

Rasvasynteesi, or fatty acid synthesis, is the metabolic process by which organisms synthesize fatty acids from simpler precursor molecules. This process is fundamental for energy storage, as fatty acids are a major component of triglycerides, the primary form of stored energy in animals. It also plays a crucial role in the synthesis of cell membranes, as phospholipids are built from fatty acids.

In eukaryotes, fatty acid synthesis primarily occurs in the cytoplasm, with the key enzyme being fatty acid synthase. This multi-enzyme complex catalyzes a series of reactions that elongate a growing fatty acid chain by two-carbon units. The initial substrate is typically acetyl-CoA, which is transported from the mitochondria to the cytoplasm. The process requires a reducing agent, primarily NADPH, which is generated through pathways like the pentose phosphate pathway.

The synthesis starts with the formation of malonyl-CoA from acetyl-CoA by acetyl-CoA carboxylase, a rate-limiting step regulated by hormones and nutrient availability. The fatty acid synthase then repeatedly adds two-carbon units from malonyl-CoA to an acetyl-CoA primer, releasing CO2 in each cycle. This process continues until a fatty acid of a desired length, commonly palmitate (16 carbons), is produced.

In prokaryotes, fatty acid synthesis also occurs in the cytoplasm, but the enzymes are often separate proteins rather than a large complex. The overall biochemical pathway is similar, involving acetyl-CoA, malonyl-CoA, and NADPH.

Beyond energy storage and membrane structure, fatty acids synthesized through this pathway are precursors for other important molecules, including eicosanoids, which are signaling molecules involved in inflammation and blood clotting. The regulation of rasvasynteesiä is tightly controlled by hormonal signals and the energy status of the cell, ensuring that energy reserves are appropriately managed.