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The cytosolic acetyl-CoA can also condense with acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA which is the rate-limiting step controlling the synthesis of cholesterol. [16] Cholesterol can be used as is, as a structural component of cellular membranes, or it can be used to synthesize steroid hormones , bile salts , and vitamin D .
Synthesis within the body starts with the mevalonate pathway where two molecules of acetyl CoA condense to form acetoacetyl-CoA. This is followed by a second condensation between acetyl CoA and acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl CoA . [38] This molecule is then reduced to mevalonate by the enzyme HMG-CoA reductase.
The synthesis of even-chained fatty acid synthesis is done by assembling acetyl-CoA precursors, however, propionyl-CoA instead of acetyl-CoA is used as the primer for the biosynthesis of long-chain fatty acids with an odd number of carbon atoms. [19] Regulation. In B. subtilis, this pathway is regulated by a two-component system: DesK and DesR.
Besides its role in the synthesis of ketone bodies, HMG-CoA is also an intermediate in the synthesis of cholesterol, but the steps are compartmentalised. [1] [2] Ketogenesis occurs in the mitochondria, whereas cholesterol synthesis occurs in the cytosol, hence both processes are independently regulated. [2]
Cholesterol can be made from acetyl-CoA through a multiple-step pathway known as isoprenoid pathway. Cholesterols are essential because they can be modified to form different hormones in the body such as progesterone. [6] 70% of cholesterol biosynthesis occurs in the cytosol of liver cells. [citation needed]
Cholesterol is synthesized from acetyl CoA. [12] The pathway is shown below: 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.
Acetoacetyl CoA is the precursor of HMG-CoA in the mevalonate pathway, which is essential for cholesterol biosynthesis. It also takes a similar role in the ketone bodies synthesis ( ketogenesis ) pathway of the liver . [ 1 ]
Sterol O-acyltransferase (also called Acyl-CoA cholesterol acyltransferase, Acyl-CoA cholesterin acyltransferase [citation needed] or simply ACAT) is an intracellular protein located in the endoplasmic reticulum that forms cholesteryl esters from cholesterol. Sterol O-acyltransferase catalyzes the chemical reaction: