Fatty acid synthesis occurs in the cytoplasm. It occurs mostly in adipose tissue, the liver and lactating mammary glands. Acetyl-CoA is required to begin fatty acid synthesis. It can be obtained by converting citrate to acetyl-CoA through the action of ATP citrate lyase.
Acetyl-CoA is typically located in the mitochondrial matrix of cells, but must be shuttled to the cytoplasm in order to participate in fatty acid synthesis. This is done via the citrate shuttle, which forms citrate from acetyl-CoA and shuttles it through the mitochondrial membranes and into the cytoplasm. In the cytoplasm, ATP citrate lyase then converts citrate to acetyl-CoA.
Acetyl-CoA Carboxylase is the rate-limiting enzyme in fatty acid synthesis. This enzyme processes acetyl-CoA with the help of biotin to create malonyl-CoA. Positive regulators for this enzyme include insulin and citrate, while negative regulators include glucagon and palmitoyl-CoA.
Biotin is required as a cofactor for the enzyme acetyl-CoA carboxylase to function. Biotin provides a unit of CO2 to the reaction.
Malonyl-CoA represents the first dedicated molecule in the fatty acid synthesis pathway. It is acted upon by fatty acid synthase to form palmitate, a 16-carbon fatty acid which is the precursor to longer fatty acids.
Fatty acid synthase is a complex of enzymes responsible for creating and elongating fatty acids. Malonyl-CoA is initially acted upon by fatty acid synthase to form palmitate, a 16-carbon fatty acid.
Triglycerides are energy storage molecules composed of three fatty acids attached to a glycerol. Glycerol is combined with fatty acids through the help of glycerol-3-phosphate acyltransferase.
Glycerol-3-phosphate acyltransferase is an enzyme which uses glycerol and fatty acids as substrates to create triglycerides.
Triglycerides are created when glycerol is combined with three fatty acids. Triglycerides can then be stored or packaged as lipoproteins (eg., VLDL) for distribution throughout the body.
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