The biosynthesis of Hexadecanoic Acid is carried out in chloroplasts and protoplasts in plants to synthesize saturated fatty acids with 4 to 16 carbons and more than 16 carbons. Animals are carried out in the cytosol, only 16-carbon saturated fatty acids are synthesized, and fatty acids longer than 16 carbons are synthesized in the endoplasmic reticulum or mitochondria. As far as the synthesis process of 16-carbon saturated fatty acids in the cytosol is concerned, it is similar to the β-oxidation process, but the synthesis process is not a simple reversal of the β-oxidation process.
The similarities and differences between Hexadecanoic Acid synthesis and fatty acid β-oxidation can be summarized as follows:
① The places where the two pathways occur are different, β-oxidation is mainly carried out in mitochondria, and the de novo synthesis of saturated fatty acids is carried out in cytosol;
② Both pathways have an intermediate connected to the carrier, fatty acid is synthesized into ACP, and β-oxidized into CoA;
③ There are 4-step reactions in both pathways. Fatty acid synthesis is condensation, reduction, dehydration and reduction, and fatty acid β-oxidation is dehydrogenation, water addition, dehydrogenation and thiolysis. Although the two are reverse reactions from the chemical approach. However, their reaction processes are different, and the cofactors used are also different;
④ Both pathways have a raw material transport mechanism. In fatty acid synthesis, there is a tricarboxylic acid transport mechanism that transports acetyl CoA from mitochondria to cytoplasm. In degradation, there is a carnitine carrier system that transports fatty acyl CoA from cytoplasm to mitochondria;
⑤Both pathways are characterized by successive changes in fatty acid chains. In fatty acid synthesis, fatty acid chains obtain 2-carbon units and are successfully extended. In degradation, 2-carbon units in the form of acetyl CoA leave to achieve fatty acid chain shortening;
⑥Hexadecanoic Acid is synthesized from the methyl end of the molecule to the carboxyl end, and the degradation is in the opposite direction, with the departure of the carboxyl group as the first step.
⑦ The hydroxyester-based intermediate is D-configuration in fatty acid synthesis, but L-configuration in degradation;
⑧ Fatty acid synthesis is composed of a reduction pathway, which requires the participation of NADPH, and fatty acid decomposition is composed of an oxidation pathway, which requires the participation of FAD and NAD+;
⑨In animals, fatty acid synthase is a multifunctional enzyme composed of a polypeptide chain, and the decomposition of fatty acid is catalyzed by a variety of enzymes.
⑩β-oxidation is a process that produces a large amount of energy in addition to initial activation energy consumption. De novo synthesis of saturated fatty acids is an energy-intensive process.
The above are the important similarities and differences between fatty acid synthesis in cytosol and β-oxidation in mitochondria. In mitochondria, the synthesis reaction of Hexadecanoic Acid is the reverse process of β-oxidation reaction
