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This is the next-to-last step of cholesterol biosynthesis. [4] Defective synthesis results in the human inherited disorder lathosterolosis resembling Smith–Lemli–Opitz syndrome. [4] Mice where this gene has been deleted lose the ability to increase vitamin D 3 in the blood following UV exposure of the skin. [5]
Cholesterol is the principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. [3] [4]Cholesterol is biosynthesized by all animal cells [citation needed] and is an essential structural and signaling component of animal cell membranes.
Cholesterol is bio-synthesised from mevalonate via a squalene cyclisation of terpenoids. Cell membranes require high levels of cholesterol – typically an average of 20% cholesterol in the whole membrane, increasing locally in raft areas up to 50% cholesterol (- % is molecular ratio). [ 6 ]
SQS synthase catalyzes the branching point between sterol and nonsterol biosynthesis, and commits farnesyl pyrophosphate (FPP) exclusively to production of sterols. [2] An important sterol produced by this pathway is cholesterol, which is used in cell membranes and for the synthesis of hormones. [22]
Fatty acid synthesis occurs in the cytoplasm of cells while oxidative degradation occurs in the mitochondria. Many of the enzymes for the fatty acid synthesis are organized into a multienzyme complex called fatty acid synthase. [5] The major sites of fatty acid synthesis are adipose tissue and the liver. [6]
Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown and storage of fats for energy and the synthesis of structural and functional lipids, such as those involved in the construction of cell membranes. In animals, these fats are obtained from food and are synthesized by the liver. [1]
Cholesterol synthesis pathway. More generally, this synthesis occurs in three stages, with the first stage taking place in the cytoplasm and the second and third stages occurring in the endoplasmic reticulum. [9] The stages are as follows: [12] 1. The synthesis of isopentenyl pyrophosphate, the "building block" of cholesterol 2.
Lanosterol is a key four-ringed intermediate in cholesterol biosynthesis. [6] [7] In humans, lanosterol synthase is encoded by the LSS gene. [8] [9] In eukaryotes, lanosterol synthase is an integral monotopic protein associated with the cytosolic side of the endoplasmic reticulum. [10]