User:Moh.modassir/sandbox

Much of the cholesterols ynthesisin vertebratest akes place in the liver. A small fraction of the cholesterol madet herei s incorporatedin to the membraneso f hepatocytes, but most of it is exported in one of three forms: biliary cholesterolb, ile acids,o r cholesteryel sters.B ile acids and their salts are relatively hydrophilic cholesterol derivatives that are slrrthesized in the liver and aid in lipid digestion (see Fig. 17-1). Cholesteryl esters are formed in the liver through the action of acyl- CoA-cholesterol acyl transferase (ACAT). This enzyrne catalyzes the transfer of a fatty acid from coenzyme A to the hydroxyl group of cholesterol (Fig. Zl-38), convertingt he cholesterotlo a moreh ydrophobic form. Cholesteryel stersa re transportedi n secreted lipoprotein particles to other tissues that use cholesterol, or they are stored in the liver All growing animal tissues need cholesterol for membrane syrrthesis, and some organs (adrenal gland and gonadsf,o r example)u sec holesteroal sa precursor for steroidh ormonep roduction( discussedb elow).C holesterol is also a precursor of vitamin D