Phospholipid Metabolism PDF

Phospholipids Level : 1st level Semester: 1st semester Module: BSF112 Module  Prepared by Dr. Shaymaa M. Abdelrahman Medical Biochemistry Department  Learning outcomes By the end of the lectures, the students will be able to: Define phospholipids. Identify general...

Phospholipids Level : 1st level Semester: 1st semester Module: BSF112 Module  Prepared by Dr. Shaymaa M. Abdelrahman Medical Biochemistry Department  Learning outcomes By the end of the lectures, the students will be able to: Define phospholipids. Identify general structure of phospholipids. Classify and describe phospholipids. Identify structural functions of phospholipids.  Importance in diet Phospholipids are present in high concentrations in the brain, egg yolk, liver and kidney. They are not essential dietary components. Phospholipids are complex (compound) lipids. Phospholipids are amphipathic Classification Glycerol & sphingosine Phosphatidic acid Phosphatidylcholine (Lecithin)  Functions 1) Lecithin enters in the structure of cell membrane. It is the most abundant phospholipid in cell membrane. 2) Lecithin acts as lipotropic factor i.e. prevent accumulation of fat in liver (fatty liver) 3) Lecithin prevents gall stones: Lecithin in bile solubilizes cholesterol and prevent cholesterol stones in gall bladder. 4) Lecithin acts as body store of choline. Choline is important for nerve transmission and transmethylation. 5) Lecithin forms cholesterol esters (in the presence of LCAT enzyme): Lecithin + Cholesterol → Cholesterol ester + Lysolecithin Cholesterol esters is transported to the liver and excreted with bile. This prevents atherosclerosis. Lecithin is a natural surfactant 6) Dipalmitoyl lecithin (i.e. lecithin containing 2 palmitic acid residues) acts as a surfactant in the lung It is continuously secreted by the lung cells in the alveolar wall, forming monolayer over the watery surface of the alveolus. It lowers the surface tension and prevents the alveoli from collapse.. Phosphatidylethanolamine (Cephalin) Phosphatidylserine Phosphatidylinositol Plasmalogens The pathway for synthesis of plasmalogens occurs in the peroxisomes. It contains a vinyl-ether and an ester bond at the sn-1 and sn-2 positions, respectively, in the glycerol backbone. They constitutes about 10% of the phospholipids present in brain and muscles. Cardiolipin (CL) Each CL possesses a glycerol backbone connected to two phosphatidyl lipids. Cardiolipin is the major lipid in mitochondrial membrane It stimulates antibody formation i.e. antigenic. Sphingomyelin Sphingomyelin consists of phosphocholine head group, a sphingosine, and a fatty acid. It is one of the few membrane phospholipids not synthesized from glycerol. The sphingosine and fatty acid (usually unsaturated) can collectively be categorized as a ceramide. Summary of functions of phospholipids Phospholipids form an essential component of plasma lipoproteins. Phospholipids enter into the structure of cell membranes, myelin sheath, mitochondria and lung alveoli. Source of arachidonic acid. This is the substrate for the formation of prostanoids, leukotriens and lipoxins in the cell. Hypersensitivity and inflammatory reactions Phosphatidic acid is produced as an intermediate in the synthesis of triacylglycerols and phospholipids. Cephalin is one of activating factors of coagulation mechanism. Phosphatidylserine plays a role in cell cycle signalling, specifically in relation to apoptosis. Phosphatidylinositol acts as precursor of second messenger (inositol triphosphate), mediating hormonal action inside cells. The lecithin-sphingomyelin ratio (L/S ratio or L-S ratio) is the traditional standard for fetal lung maturity testing.  Formative questions Lecithin and cephalin are: Lecithin is phospholipid its a) Neutral fats main component (s) is/are? a) Glycerol + 2 fatty acids + b) Glycolipids H3PO4 + Choline c) Waxes b) Glycerol + H2PO4 + Choline d) Phospholipids c) Glycerol + 3 fatty acids d) Only glycerol  Formative questions What is the other name of Plasmalogen synthesis lecithin? takes place in a) Phosphatidylcholine a) Rough endoplasmic b) Phosphatidylserine reticulum c) Cardiolipin b) Smooth endoplasmic reticulum d) Sphingomyelin c) Mitochondria d) Peroxisome  Formative questions Which of the following is a Which of the following lipids cephalin act as lungs surfactants? a) Phosphatidylserine a) Phosphatidylcholine b) Phosphatidylethanolamine b) Phosphatidylethanolamine c) Phosphatidylcholine c) Ceramide d) Phosphatidylinositol d) Phosphatidylinositol  Formative questions A phospholipid consists of a a. Polar phosphate hydrophilic tail group and hydrophobic fatty acid head b. Non-polar phosphate containing head group and polar fatty acid tail c. Polar phosphate containing hydrophilic head group and hydrophobic fatty acid tail d. Non-polar phosphate containing head group and non-polar fatty acid tail  Formative questions Which of the following is Which of the following mostly present in phospholipids plays an mitochondrial membranes? important role in apoptosis? a. Lecithin a. Dipalmitoyl lecithin b. Cephalin b. Cardiolipin c. Cardiolipin c. Phosphatidylinositol d. Ceramide d. Phosphatidylserine  Formative questions Which of the following Lecithin/cholesterol phospholipids play an acyltransferase (LCAT converts important role in cholesterol to cholesteryl mitochondrial function esters) a. Dipalmitoyl lecithin a. True b. Cardiolipin b. False c) Phosphatidylinositol d) Phosphatidylserine  Formative questions Classify phospholipids Enumerate two examples for glycerophospholipids Name one example for sphingophospholipids