Fatty acid elongation

Fatty acid elongation is the enzyme-driven addition of two-carbon units to an existing fatty-acid chain. It occurs mainly in the endoplasmic reticulum and mitochondria, using distinct enzyme systems.

Elongase: An enzyme that catalyzes a step in the extension of a fatty-acid chain by two carbon atoms. Elongases initiate each cycle by condensing an acyl chain with malonyl-CoA.
Fatty acid: A carboxylic acid with a hydrocarbon chain, found as a component of lipids and as a metabolic fuel. Elongation changes the chain length of this broader class of molecules.
Very-long-chain fatty acid: A fatty acid with a chain length commonly defined as 22 or more carbon atoms. These products depend on repeated elongation beyond the lengths made by fatty acid synthase.
Mitochondrial fatty acid synthesis: A pathway in mitochondria that synthesizes fatty acids using a distinct set of enzymes from the cytosolic system. It extends chains in mitochondria, unlike the principal endoplasmic-reticulum elongation pathway.
Fatty acid synthase: A multifunctional enzyme complex that builds fatty acids from acetyl-CoA and malonyl-CoA, chiefly producing palmitate. Unlike fatty acid synthase, elongases extend pre-existing chains through separate enzyme reactions.
Acyl-CoA: A molecule in which a fatty-acid-derived acyl group is linked to coenzyme A by a high-energy thioester bond. Most elongation substrates are activated as acyl-CoA molecules.
Sphingolipid: A class of membrane lipids built on a sphingoid base and containing at least one fatty-acid-derived component. Elongated fatty acids contribute to the distinctive composition of many sphingolipids.
Beta oxidation: A metabolic pathway that degrades fatty-acyl-CoA molecules by removing two-carbon units. It shortens fatty-acid chains, reversing elongation's overall change in chain length.
Malonyl-CoA: A three-carbon coenzyme A derivative that donates two carbon atoms during fatty-acid synthesis and elongation. Its decarboxylative condensation supplies the two-carbon increment in each elongation cycle.
Acetyl-CoA: A two-carbon thioester that transfers acetyl groups into metabolic pathways. It supplies the acetyl primer for mitochondrial fatty-acid chain extension.

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