Taif University College of Medicine Preparatory Year Students Medical chemistry (2) Part II (Lipids) week 5 lectures 1435-36 Glycerides ,Non-glyceride lipids Membranes Lipids

Lectures outlines Definition and importance of lipids Classification of lipids Fatty acids structure and properties Important reactions of FA Glycerides Non-glyceride lipids Membranes Lipids

Phospho-glycerides

Phospho-glycerides A glycerophospholipid is a lipid that contains two fatty acids and a phosphate group esterified to a glycerol molecule and an alcohol esterified to the phosphate group.

Glycerophospholipids

Lecture notes (Dr Gaber Shehab) PhosphoLipids Phospho-glycerides inositol Phosphatidyl ethanolamine (cephalin) Phosphatidyl choline (lecithin-emulsifier) Phosphatidyl ester Phosphatidyl serine Biochemistry Department

The Importance and functions of phospholipids are : 1- Amphipathic molecules they form micelles in water. 2- Good emulsifying factors. 3- Lung surfactant mainly of dipalmitoyl-lecithin, the lack of which is responsible for respiratory distress syndrome in premature infants. 4- Prevent deposition of cholesterol (biliary calculi). 5- Constituents of lipid bilayer in cell membranes 6- Provide arachidonic acid for synthesis of eicosanoids. 7- Essential for blood clotting, as they provide the platelet activating factor (PAF)

Lipids Classification Eicosanoides

Lecture notes (Dr Gaber Shehab) Nonglyceride Lipids A- Sphingolipids Sphingolipids are derivatives of ceramide (an amide between a fatty acid and sphingosine) and an amino alcohol. Ceramide Structure Sphingolipids Do not contain glycerol, but they do contain the long chain amino alcohol sphingosine, from which this class of compounds takes its name. Sphingolipids are found in both plants and animals; they are particularly abundant in cell membranes in the nervous system. The simplest compounds of this class are the ceramides, which consist of one fatty acid linked to the amino group of sphingosine by an amide bond. In sphingomyelins the primary alcohol group of sphingosine is esterified to phosphoric acid, which in turn is esterified to another amino alcohol, choline. Sphingophospholipids (Sphingomyelins ) Sphingoglycolipids (Cerebrosides & Gangliosides) Biochemistry Department

Sphingomyelins Fatty acid . It contains sphingosine (sphingol) which is 18 carbon amino alcohol fatty acids are linked to sphingosine to form ceramide, which is connected to phoshocholine to form sphingomyelin. Choline Phosphate group present in cell membranes specially of the lungs and brain mainly in the myelin sheath

Sphingoglycolipids Gangliosides Cerebrosides (Monosaccharide) (Oligosaccharide) Cerebrosides (Monosaccharide) are carbohydrate-containing ceramide derivatives (in the outer face of plasma membranes) Glycosphingolipids at the cell surface are sites of recognition. They found mainly in the myelin sheath and cell membrane of RBCs. They act as cell membrane receptors for hormones and external stimuli. They provide recognition properties.

Lecture notes (Dr Gaber Shehab) Nonglyceride Lipids Cerebrosides Glucocerebrosides occur in the plasma membrane of non-neuronal cells Galactocerebrosides occur in the plasma membrane of neurons Gangliosides Example: blood group identification Do not contain glycerol, but they do contain the long chain amino alcohol sphingosine, from which this class of compounds takes its name. Sphingolipids are found in both plants and animals; they are particularly abundant in cell membranes in the nervous system. The simplest compounds of this class are the ceramides, which consist of one fatty acid linked to the amino group of sphingosine by an amide bond. In sphingomyelins the primary alcohol group of sphingosine is esterified to phosphoric acid, which in turn is esterified to another amino alcohol, choline. Oligosaccharide linked to ceramide Biochemistry Department

Nonglyceride Lipids: B-Steroids Cholesterol Cholesterol is a C27 steroid molecule that is: a component of cell membranes a precursor for other steroid-based lipids: bile acids steroid hormones Vitamin D3 (cholecalciferol) Blood level of cholesterol: ranging from 100 to 200 mg/dL (30% as free cholesterol and 70% as cholesteryl esters) Hazards of hyperchosterolemia: Increased plasma level of cholesterol predisposes to atherosclerosis and coronary heart diseases.

Steroid Hormones Are Oxidized cholesterol derivatives Function as: sex hormones metabolic regulation Anti-inflammatory compounds male sex hormone (testis female sex hormone (ovaries, placenta) glucose metabolism, salt excretion (adrenal gland) antiinflammatory compounds

Bile acids A bile acid is a cholesterol derivative that functions as a lipid-emulsifying agent in the aqueous environment of the digestive tract. Obtained by oxidation of cholesterol Functions: Conversion of cholesterol to bile salt is an important mechanism for removal of excess cholesterol from blood. prevent precipitation of cholesterol   They are good emulsifying factors important for digestion and absorption of fats.

Lipids Classification Eicosanoides

Nonglyceride Lipids C) Waxes Are esters of long-chain fatty acids with long-chain alcohols (a very high melting point) Example: Triaconoylpalmitate, a major component of bees wax Functions: energy stores water-repellent

Nonglyceride Lipids : D-Eicosanoids Eicosanoids are important regulatory molecules Referred to as local regulators (Function where they are produced). Three classes: Prostaglandins, Thromboxanes, and Leukotrienes Prostaglandins – mediate pains sensitivity, inflammation and swelling Thromboxanes – involved in blood clotting, constriction of arteries Leukotrienes – attract white cells, involved inflammatory diseases (asthma, arthritis, etc..)

Prostaglandins Prostaglandins have: 20 carbon atoms in their fatty acid chains. An OH on carbon 11 and 15. A trans double bond at carbon 13.

Prostaglandins in the Body Prostaglandins are: Produced by injured tissues. Involved in pain, fever, and inflammation. Not produced when anti-inflammatory drugs such as aspirin inhibit their synthesis. For more information about prostaglandins please visit: http://www.elmhurst.edu/~chm/vchembook/555prostagland.html

Biomembranes

Biomembranes

Lipid Structure Hydrophilic head – H2O loving – due to polar group in the head Hydrophobic tail – H2O hating – due to the long hydrocarbon tails

Membrane Lipids hydrophilic head hydrophobic fatty acid tail

General characteristics of membrane lipids hydrophilic head Structure of phospholipids Glycerol phospholipids contain two fatty acids joined to glycerol. The fatty acids may be different from each other and are designated R1 and R2. The third carbon of glycerol is joined to a phosphate group (forming phosphatidic acid), which in turn is frequently joined to another small polar molecule (forming phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, or phosphatidylinositol). In sphingomyelin, two hydrocarbon chains are bound to a polar head group formed from serine instead of glycerol. hydrophobic fatty acid chains Structure of phospholipids

A space-filling model of a typical phospholipid bilayer Membrane Lipids Because their fatty acid tails are poorly soluble in water, phospholipids spontaneously form bilayers in aqueous solutions, with the hydrophobic tails buried in the interior of the membrane and the polar head groups exposed on both sides, in contact with water Figure 5-30. A space-filling model of a typical phospholipid bilayer. The hydrophobic interior is generated by the fatty acyl side chains. Some of these chains have bends caused by doublebonds. The different polar head groups all lie on the outer, aqueous surface of the bilayer. A space-filling model of a typical phospholipid bilayer

Important Classes of Lipids Glycerol backbone Sphingosine backbone

Question

To which class of lipids belong the following molecules?