Fatty acid synthesis

Fatty acid synthesis builds fatty-acid chains from acetyl-CoA and malonyl-CoA through repeated carbon-addition and reduction steps. In animals, its main product is palmitate.

Acetyl-CoA carboxylase: An enzyme that uses ATP and bicarbonate to convert acetyl-CoA into malonyl-CoA. It supplies the malonyl-CoA that commits carbon to chain building.
Acetyl-CoA: A two-carbon thioester that carries acetyl groups into metabolic reactions. It provides the initiating acetyl group and the carbon used to make malonyl-CoA.
Insulin: A peptide hormone that lowers blood glucose and promotes nutrient storage in responsive tissues. It promotes fatty-acid synthesis after feeding by increasing enzyme activity and expression.
Beta oxidation: A pathway that breaks fatty acids into acetyl-CoA units while producing reduced electron carriers. It degrades fatty acids, opposing the chain-building direction of synthesis.
Fatty acid synthase: A multifunctional enzyme complex that assembles fatty-acid chains from acetyl-CoA and malonyl-CoA. Its catalytic domains carry out the successive reactions of chain elongation.
Glycolysis: A metabolic pathway that converts glucose into pyruvate while producing ATP and NADH. Its products can supply mitochondrial acetyl-CoA for export to cytosolic lipid synthesis.
AMP-activated protein kinase: A cellular energy sensor that responds to low energy by regulating metabolic enzymes. It inhibits acetyl-CoA carboxylase when cellular energy is scarce.
Fatty acid elongation: A set of reactions that extends existing fatty-acid chains, mainly in the endoplasmic reticulum. It lengthens fatty acids after synthesis rather than building the initial chain from acetyl units.
Acyl carrier protein: A protein that carries growing acyl groups through fatty-acid synthesis using a phosphopantetheine arm. Its flexible arm moves intermediates between catalytic sites in the synthase.
Citrate shuttle: A transport process that moves acetyl units from mitochondria to the cytosol as citrate. It provides cytosolic acetyl-CoA when mitochondrial acetyl-CoA cannot cross the inner membrane.

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