Phospholipids are polar, ionic compounds made up of an alcohol and linked by a phosphodiester bond to either diacylglycerol or sphingosine. Phospholipids are synthesised from phosphatidic acid and 1,2-diacyl glycerol, intermediate in the production of triacylglycerol. Phospholipid synthesis occurs in the smooth endoplasmic reticulum.
In the liver, glycerol is activated by glycerol kinase. This enzyme is absent in adipose tissue. In both adipose tissues, glucose serves for glycerol 3-phosphate. Dihydroxyacetone phosphate (DHAP) produced in glycolysis is reduced by glycerol 3-phosphate dehydrogenase to glycerol 3-phosphate. Glycerol 3-phosphate acyltransferase catalyses the transfer of an acyl group to produce lysophosphatidic acid. DHAP can…
Triacylglycerol (TG) synthesis mostly occurs in liver and adipose tissue and, to a lesser extent, in other tissues. Fatty acids and glycerol must be activated prior to the synthesis of triacylglycerol.
7-Dehydro cholesterol is an intermediate in the pathway of cholesterol biosynthesis and is converted in the skin to previtamin-D3 by irradiation with UV rays of the sun. Previtamin-D3 is converted thermally and slowly to the double bond isomers by a nonenzymatic reaction to the biologically active vitamin, cholecalciferol (vitamin D3).
Cholesterol is also converted to sex hormones by the way of Δ5-pregnenolone. Progesterone can be formed and further converted to testosterone. Progesterone can enter an alternate pathway to form dehydroxyepiandrosterone. This compound can be converted to 17-β estradiol action of 17-reductase. Also, estradiol can be formed from testosterone by the action of the aromatase system. Steroid…
Conversion of cholesterol to adrenal cortical hormones Cholesterol is the major precursor and undergoes side chain cleavage to form Δ5–pregnenolone, releasing a C6 aldehyde, isocaproaldehyde, Δ5-pregnenolone is mandatory in the synthesis of all steroid hormones. Pregnenolone can be converted directly to progesterone, which requires two plasmic enzymes, 3-β-OH dehydrogenase and Δ4.5 isomerase. The dehydrogenase converts the 3 OH…
The steroid hormones are majorly synthesised by two ways:
Adrenal cortex, ovaries, testis, cytoplasm, and mitochondria are the sites of synthesis of bile salts.
Cholesterol is the precursor for the synthesis of five classes of steroid hormones: Glucocorticoids Example: Cortisol Mineralocorticoids Example: Aldosterone Progestins Example: Progesterone Androgens Example: Testosterone Estrogens Example: Estradiol