Triglyceride and phospholipid synthesis and degradation

Theoreticcally ester bond is formed by the withrawal of H2O, but in the body FA-CoA is necessary, that contains high group transfer potential thioester bond and enzymes. The more the cis configuration FA and the more double bond is found in FA, the less London-forces are possible between fatty acids, so the lipid is more fluid, the stiffening point is higher. Compare pig fat and sunflower oil.

Characteristics and function of triacylglycerides hydrofobic neutral fats most efficient food stores, because: many H-atoms of FAs can burn in oxidative phosphorylation to water coupled to the formation of many ATP on the contrary: glucose is partially oxidized in glycogen as hydrofobic molecules, they interact with each other in small place, but not with water, compared to glycogen that absobs many water, forms gel heat insulators: animals that sleep in winter or live in cold water or near to poles bear thick fat layer under their skin mechanical protection is given to organs during movement, strike

Phospholipids are amphipathic molecules: hydrophilic and hydrophobic parts are separated.

Phospholipids form lipid bilayer in every membrane in the cells, hydrophilic head orients toward the water phase. In the membranes cholesterol, peripheral and integral proteins are found. Glycosylated lipids and proteins are in the outer leaflet. signal transduction moleculeas are liberated from membranes: IP3, DAG, PGE2, PGI2, TXA2, HETE, PAF

Monolayer phospholipids Hydrophobic triglycerides and cholesterol esters are packed in monolayer phospholipids and proteins in the blood and lymph. The non stoichiometric aggregate is called lipoprotein. mixed micell formed during lipid digestion in gut simple micell

Phospholipases 1st acyl group is cut by PLA1 or PLB after PLA2 = saturated = unsaturated 2nd acyl group is cut by PLA2 or LCAT in blood PLC can be specific for phosphatidyl inositol signal transduction

Common steps in triacylglyceride and phosholipid synthesis in liver

From Phosphatidic acid (in middle) the synthesis of tiglyceride (on the botton) and two kind of phospholipid: phosphatidyletanolamine and phosphatidylcholine (on sides and bellow)

Synthesis of triglycerides in the enterocytes proceeds with alternative mechanism: does not need phosphatidic acid, nor glycerol, nor glcolysis intermedier, just monoglyceride and FA derived from food lipids are enough. chylomicron lipoprotein lymphatic system blood phospholipids + proteins

phosphatidyiletanolamine and phosphatidylserine interconversion Phosphatidylcholine, phosphatidyiletanolamine and phosphatidylserine interconversion ―N+―(CH3)3 foszfatidylcholine > 3 SAH methyltransferase LIVER 3 SAM liver

Phosphatidylinositol and cardiolipin synthesis phosphatidylinositol- trisphosphate = PIP3 DAG inositol-trisphosphate =IP3 signal transduction

= regulation of lipolysis in adipocyte adrenal cortex tissues liver MAG-lipáz

Triglyceride digesting enzymes each hydrolyses ester bond the acitive site of some lipases equals to serine proteases’ active centre: Ser, His, Asp, a Ser OH attacks ester bond carbonyl C-atom enzyme name source place of effect substrate product lingual lipase salivary gland stomach milk fat 1,2-DAG+ FA gastric lipase stomach stomach milk fat 1,2-DAG + FA pancreas lipase pancreas small intestine each TAG 2-MAG +2 FA + colipase non specific lipase+ pancreas small intestine many lipids e.g. glycerol + FA bile acids 2-MAG hormonsensitive lipase cells cells each TAG 2-MAG + 2FA MAG-lipase cells cells 2-MAG glycerol + FA hepatic lipase hepatocyte liver sinusoids lipoprot. TAG 2-MAG + 2 FA lipoprotein lipase parenchymal cell blood lipoprot. TAG 2-MAG + 2FA + apoprot. C2

From Ceramide synthesis of cerebroside, sphingomyelin and gangliozids