Lesson 6: Structure and Function of Lipids PDF

STRUCTURE AND FUNCTION OF LIPIDS Mr. Brylle Raphael U. Bigcas College of Arts and Sciences Manila Central University  OUTLINE OF DISCUSSION Introduction to Lipids Classification of Lipids Biological Function of Lipids Prolonged Fasting of Polar Bears and Triglycerides Sn...

STRUCTURE AND FUNCTION OF LIPIDS Mr. Brylle Raphael U. Bigcas College of Arts and Sciences Manila Central University  OUTLINE OF DISCUSSION Introduction to Lipids Classification of Lipids Biological Function of Lipids Prolonged Fasting of Polar Bears and Triglycerides Snake Venom and Glycerophospholipid Degradation Moby Dick and Spermaceti Why Do Plants Emit Isoprenoids?  LIPIDS Lipids are a class of biological molecules defined by low solubility in water and high solubility in nonpolar solvents. Primarily are hydrocarbons Lipids represent highly reduced forms of carbon and upon oxidation in metabolism, yield large amounts of moleculse of choice for metabolic energy storage.  CLASSIFICATION OF LIPIDS 1. Fatty acids and their derivatives 2. Triacylglycerols 3. Wax Esters 4. Phospholipids (Phosphoglycerides and sphingomyelin) 5. Sphingolipids (other than sphingomyelin that contain amino alcohol sphingosine) 6. Isoprenoids (molecules that appear to be made up of multiple copies of isoprene) The lipids found in biological systems are either hydrophobic (containing only non polar groups)or amphipathic, which means they possess both polar and non polar groups. The hydrophobic nature of lipid molecules allows membranes to act as effective barriers to more polar molecules.  FATTY ACIDS A fatty acid is composed of a long hydrocarbon chain (“tail”) and a terminal carboxyl group (or “head”). The carboxyl group is normally ionized under physiological conditions. Most of the fatty acids found in nature have an even number of carbon atoms (usually 14 to 24). Fatty acids are either saturated (all carbon–carbon bonds are single bonds) or unsaturated (with one or more double bonds in the hydrocarbon chain). If a fatty acid has a single double bond, it is said to be monounsaturated and if it has more than one, polyunsaturated. Fatty acids can be named or described in at least three ways: Free rotation around each of the carbon–carbon bonds makes saturated fatty acids extremely flexible molecules. Saturated fatty acids adopt the straight conformation Unsaturated fatty acids are slightly more abundant in nature than saturated fatty acids, especially in higher plants. The most common unsaturated fatty acid is oleic acid, or 18:1(9), with the number in parentheses indicating that the double bond is between carbons 9 and 10. The number of double bonds inan unsaturated fatty acid varies typically from one to four, but, in bacteria, this number rarely exceeds one. Most double bonds of fatty acids existing in nature are in cis conformation SO WHAT? SATURATED FATTY ACIDS Formula Common Name Melting Point lauric acid 45 ºC myristic acid 55 ºC palmitic acid 63 ºC stearic acid 69 ºC arachidic acid 76 ºC UNSATURATED FATTY ACIDS Formula Common Name Melting Point palmitoleic acid 0 ºC oleic acid 13 ºC linoleic acid -5 ºC linolenic acid -11 ºC arachidonic acid -49 ºC SO WHAT? Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty acids include linoleic and linolenic acids. These must be obtained by mammals in their diet (specifically from plant sources). At least one function of the essential fatty acids is to serve as a precursor for the synthesis of eicosanoids, such as prostaglandins, a class of compounds that exert hormone-like effects in many physiological processes Microorganisms, for example, often contain branched-chain fatty acids, such as tuberculostearic acid. Some bacteria also synthesize fatty acids containing cyclic structures such as cyclopropane, cyclopropene, and even cyclopentane rings.  TRIGLYCEROLS Also called Triglycerides. Triacylglycerols are a major energy reserve and the principal neutral derivatives of glycerol found in animals. These molecules consist of a glycerol esterified with three fatty acids. If all three fatty acid groups are the same, the molecule is called a simple triacylglycerol. Examples include tristearoylglycerol (common name tristearin) and trioleoylglycerol (triolein). Mixed triacylglycerols contain two or three different fatty acids. Triacylglycerols in animals are found primarily in the adipose tissue (body fat), which serves as a depot or storage site for lipids. Acylglycerols can be hydrolyzed by heating with acid or base or by treatment with lipases. Hydrolysis with alkali is called saponification and yields salts of free fatty acids and glycerol. This is how soap (a metal salt of an acid derived from fat) was made by our ancestors. During ancient Roman times, sacrificed animals’ ashes and fat accumulated on the SAPO Mountain, and mixed with the Tiber River as it rained. Blended with the river waters, oil, clay mud and ash formed a foamy mixture. This mixture is the natural form of the soap that we use today. Soap which were started being used during BC 3000, were described in Sumerian Inscriptions of BC 2500. It corresponds to the Roman time in BC 1000 that the substance obtained and used was named as 'Soap'. Usage of the soap for personal hygiene, which was for cleaning and treatment purposes at the time of Hippocrates, took place in the 18th century in Europe and in the 19th century in the States. Triacylglycerols are rich in highly reduced carbons and thus yield large amounts of energy in the oxidative reactions of metabolism. Complete oxidation of 1g of triacylglycerols yields about 38kJ of energy, where as proteins and carbohydrates yield only about 17kJ/g.  PHOSPHOLIPIDS A 1,2-diacylglycerol that has a phosphate group esterified at carbon atom 3 of the glycerol backbone is a glycerophospholipid, also known as a phosphoglyceride or a glycerolphosphatide. Essential components of cell membranes and are found in small concentrations in other parts of the cell. It should be noted that all glycerophospholipids are members of the broader class of lipids known as phospholipids. The numbering and nomenclature of glycerophospholipids present a dilemma in that the number 2 carbon of the glycerol backbone of a phospholipid is asymmetric. It is possible to name these molecules either as D- or L-isomers. Thus, glycerol phosphate itself can be referred to either as D-glycerol-1- phosphate or as L-glycerol-3-phosphate Other common head groups found in phosphatides include glycerol, serine, and inositol. Another kind of glycerol phosphatide found in many tissues is diphosphatidylglycerol. First observed in heart tissue, it is also called cardiolipin. In cardiolipin, a phosphatidyglycerol is esterified through the C-1 hydroxyl group of the glycerol moiety of the head group to the phosphoryl group of another phosphatidic acid molecule. Phosphatidic acid is found in small amounts in most natural systems and is an important intermediate in the biosynthesis of the more common glycerophospholipids. The phosphate, together with such esterified entities, is referred to as a “head” group. Phosphatides with choline or ethanol amine are referred to as phosphatidylcholine (known commonly as lecithin) or phosphatidylethanolamine, respectively.  SPHINGOLIPIDS Sphingolipids represent another class of lipids found frequently in biological membranes. An 18-carbon amino alcohol, sphingosine forms the backbone of these lipids rather than glycerol.  GLYCOSPHINGOLIPIDS Glycosphingolipids are consist of a ceramide with one or more sugar residues in a- glycosidic linkage at the 1- hydroxyl moiety. The neutral glycosphingolipids contain only neutral (uncharged) sugar residues. When a single glucose or galactose is bound in this manner, the molecule is a cerebroside.  GANGLIOSIDES Another class of lipids is formed when a sulfate is esterified at the 3- position of the galactose to make a sulfatide. Gangliosides are more complex glycosphingolipids that consist of a ceramide backbone with three or more sugars esterified, one of these being a sialic acid such as N- acetylneuraminic acid. Gangliosides are present in nerve endings and appear to be important in nerve impulse transmission. A number of genetically transmitted diseases involve the accumulation of specific glycosphingolipids due to an absence of the enzymes needed for their degradation. Such is the case for ganglioside GM2 in the brains of Tay-Sachs disease victims, a rare but fatal disease characterized by a red spot on the retina, gradual blindness, and loss of weight, especially in infants and children.  WAXES Waxes are esters of long-chain alcohols with long-chain fatty acids. The resulting molecule can be viewed as having a weakly polar head group (the ester moiety itself) and along, nonpolar tail (the hydrocarbon chains). Fatty acids found in waxes are usually saturated. Waxes are water-insoluble due to the weakly polar nature of the ester group. As a result, this class of molecules confers water-repellant character to animal skin, to the leaves of certain plants, and to bird feathers. The glossy surface of a polished apple results from a wax coating.  TERPENES The terpenes are a class of lipids formed from combinations of two or more molecules of 2-methyl-1,3-butadiene, better known as isoprene (a five-carbon unit that is abbreviated C5). A monoterpene (C10) consists of two isoprene units, a sesquiterpene (C15) consists of three isoprene units, a diterpene (C20) has four isoprene units, and so on. Isoprene units can be linked interpenes to form straight chain or cyclic molecules, and the usual method of linking isoprene units is head to tail. Monoterpenes occur in all higher plants, while sesquiterpenes and diterpenes are less widely known. The triterpenes are C30 terpenes and include squalene and lanosterol, two of the precursors of cholesterol and other steroids (discussed later). Tetraterpenes (C40) are less common but include the carotenoids, a class of colorful photosynthetic pigments. Long-chain polyisoprenoid molecules with a terminal alcohol moiety are called polyprenols. The dolichols, one class of polyprenols consist of 16 to 22 isoprene units and, in the form of dolichylphosphates, function to carry carbohydrate units in the biosynthesis of glycoproteins in animals. Polyprenyl groups serve to anchor certain proteins to biological membranes. The large structure is flipped form the ER membrane into the lumen of ER. Sugars are added into the ER lumen using the monosaccharides attached with dolicholphosphate. THANK YOU FOR LISTENING. Mr. Brylle Raphael U. Bigcas College of Arts and Sciences Manila Central University