Cytosol and mitochondrial fraction (ER) – enzymes involved in cholesterol synthesis are formed in these organelles.
About 1 g of cholesterol is synthesised per day in adults. Almost all the tissues of the body participate in cholesterol biosynthesis. The largest contribution is made by liver (50%), intestine (15%), skin, adrenal cortex, reproductive tissue, and so on.
Cholesterol is essential to life as it performs a number of important functions. It is a structural component of all membranes. Cholesterol is the precursor of all other steroids in the body such as corticosteroids, sex hormones, bile acids, and vitamin D. It is essential ingredient in the structure of lipoproteins from which lipids in the…
Cholesterol is present in tissues and plasma. It is available either as free cholesterol or as a storage form attached to a long chain fatty acid as cholesteryl ester. It is synthesised in many tissues from Acetyl-CoA and is ultimately eliminated from the body in the bile as cholesterol or bile salts. Cholesterol is the…
The reducing equivalents for fatty acid synthesis are provided by NADPH, which comes either from citrate (Acetyl-CoA) transport or hexose monophosphate shunt. About 50%–60% of required NADPH is obtained from hexose monophosphate shunt, which influences fatty acid synthesis.
Consumption of high carbohydrate of fat-free diet increases the synthesis of acetyl-CoA carboxylase and fatty acid synthase, which promotes fatty acid formation. On the other hand, fasting or high fat diets decreases fatty acid production by reducing the synthesis of these two enzymes.
Hormones regulate acetyl-CoA carboxylase by a separate mechanism – phosphorylation (inactive form) and dephosphorylation (active form) of the enzyme. Glucagon, epinephrine, and norepinephrine inactivate the enzyme by cAMP-dependent phosphorylation. Insulin, on the other hand, dephosphorylates and activates the enzyme. Thus, insulin promotes fatty acid synthesis while glucagons inhibits. Insulin stimulates tissues’ uptake of glucose and…
This enzyme controls the committed step in fatty acid synthesis. Acetyl-CoA carboxylase exists as an inactive promoter (monomer) or an active polymer. Citrate promotes polymer formation and hence increases fatty acid synthesis. Palmityl-CoA and malonyl-CoA cause dephosphorylation of the enzyme and, therefore, inhibits fatty acid synthesis.
Fatty acid production is controlled by enzymes, metabolites, end products, hormones, and dietary manipulation.
Elongation of fatty acid chains occurs in the endoplasmic reticulum. This pathway (the microsomal system) converts fatty Acyl-CoA derivative having two carbons more, using malonyl-CoA as acetyl donor and NADPH as reductant and is catalysed by the microsomal fatty acid elongase system of enzymes. Elongation of stearyl-CoA in brain increases rapidly during myelination in order…