THEME: Di- and p olysaccharides . Terpenes .

1. Lecture № 15 THEME: Di- and polysaccharides. Terpenes. associate. prof. Ye. B. Dmukhalska, assistant. I.I. Medvid

2. Outline 1.Oligosaccharides. 2. The following functions of carbohydrates in humans. Classification of disaccharides. 3. Polysaccharides (glucanes). a) Homopolysaccharides: b) Heteropolysaccharides. 4. Glycoconjugates. 5. Lipids: Fats. Phospholipids. Waxes. Nonsaponifiable lipids. 6. Terpenes and terpenoids. Terpene biosynthesis. Classificationofterpenes. 7. Carotenoids.Steroids. Properties of cholesterol.Biosynthesisofcholesterol. 8. Vitamins. Water-soluble vitamins. Water insoluble (lipid-soluble) vitamins.

3. Disaccharides. А monosaccharide that has cyclic forms (hemiacetal or hemiketal) can react with an alcoho1 to form а glycoside (acetal or ketal). This same type of reaction can be used to produce а disaccharide, а carbohydrate in which two monosaccharides are bonded together. In disaccharide formation, one of the monosaccharide reactants functions as а hemiacetal or hemiketal, and the other functions as an alcohol. Monosaccharide + monosaccharide = disaccharide + Н2O The bond that links the two monosaccharides of а disaccharide together is called а glycosidic linkage. А glycosidic linkage is the carbon-oxygen-carbon bond that joins the two components of а glycoside together. The bond that links the two monosaccharides of а disaccharide together is called а glycosidic linkage. We now examine the structures and properties of four important disaccharides: maltose, cellobiose, lactose, and saccharose. As we consider details of the structures of these compounds, we will find that the configuration (α or β) at carbon-1 of the reacting monosaccharides is often of prime importance.

4. Maltose, often called malt sugar, is produced by breaking down the polysaccharide starch, as takes place in plants when seeds germinate and in human beings during starch digestion. It is а common ingredient in baby foods and is found in malted milk. Malt (germinated barley that has been baked and ground) contains maltose; hence the name malt sugar. Structurally, maltose is made up of two D-glucopyranose units, one of which must be -D-glucose. The formation of maltose from two glucose molecules is as follows: -D-Glucose -D-Glucose -(1-4)-linkage

5. So, α-maltose can be named as 4-O-(α-D-glucopyranosido)-α-D-glucopyranose, β-maltose – 4-O-(α-D-glucopyranosido)-β-D-glucopyranose.

6. The glycosidic linkage between the two glucose units is called an (1 - 4) linkage. The two ОН-groups that form the linkage are attached, respectively, to carbon-1 of the first glucose unit (in an a configuration) and to carbon-4 of the second. Maltose is а reducing sugar, because the glucose unit on the right has а hemiacetal carbon atom (С-1).Thus this glucose unit can open and close; it is in equilibrium with its open-chain aldehyde form. This means there are actually three forms of the maltose molecule: -maltose, -maltose, and the open-chain form. In the solid state, the -form is dominant. The most important chemical reaction of maltose is hydrolysis. Hydrolysis of D-maltose, whether in а laboratory flask or in а living organism, produces two molecules of D-glucose.

7. CH OH CH OH CH OH CH OH 2 2 2 2 O H O O O H H H H H [ O ] H O H H H H OH H H C H OH H OH O OH OH O HO O H HO OH OH OH H OH H H H maltoboinic acid

8. CH OH CH OH CH OH CH OH 2 2 2 2 O O O O CH OH (HCl, gas) H H H H H H 3 H H H H OH OCH H 3 H OH OH O OH OH O HO HO OH OH OH H OH H H H methylmaltozide

10. Cellobiose is produced as an intermediate in the hydrolysis of the polysaccharide cellulose. Like maltose, cellobiose contains two D-glucose monosaccharide units. It differs from maltose in one of D-glucose units - the one functioning as а hemiacetal - must have а -configuration instead of the а configuration of maltose. This change in configuration gives а (1-4) glycosidic linkage. -D-Glucose (1-4)-linkage

11. α-cellobiose can be named as 4-O-(β-D-glucopyranosido)-α-D-glucopyranose, β-cellobiose – 4-O-(β-D-glucopyranosido)-β-D-glucopyranose.

12. Like maltose, cellobiose is a reducing sugar, has three isomeric forms in aqueous solution, and upon hydrolysis produces two D-glucose molecules. Despite these similarities, maltose and cellobiose have different biological behaviors. These differences are related to the stereochemistry of their glycosidic linkages. Maltase, the enzyme that breaks the glucose-glucose (1-4) linkage present in maltose, is found both in the human body and in yeast. Consequently, maltose is digested easily by humans and is readily fermented by yeast. Both the human body and yeast lack the enzyme cellobiase needed to break the glucose - glucose (1-4) linkage of cellobiose. Thus cellobiose cannot be digested by humans or fermented by yeast. In maltose and cellobiose, the two units of the disaccharide are identical - two glucose units in each case. Maltose and cellobiose have different arrangement in space. In maltose molecule α-glycosidic linkage has axial arrangement, in cellobiose molecule β-glycosidic linkage – equatorial. Its cases club-similar structure of amylose and linear structure of cellulose.

14. Lactose includes -D-galactopyranose unit and а D-glucopyranose unit joined by -(1-4) glycosidic linkage -D-galactose -D-Glucose (1-4)-linkage The glucose hemiacetal center is active when galactose bonds to glucose in the formation of lactose, so lactose is а reducing sugar (the glucose ring can open to give an aldehyde).Lactose is the major sugar found in milk. This accounts for its common name, milk sugar. Enzymes in animal mammary glands take glucose from the bloodstream and synthesize lactose in а four-step process. Epimerization of glucose yields galactose, and then the (1-4) linkage forms between а galactose and а glucose unit. Lactose is an important ingredient in commercially produced infant formulas that are designed to simulate mother' s milk. Souring of milk is caused by the conversion of lactose to lactic acid by bacteria in the milk. Pasteurization of milk is а quick-heating process that kills most of the bacteria and retards the souring process. Lactose can be hydrolyzed by acid or by the enzyme lactase, forming an equimolar mixture of galactose and glucose. In the human body, the galactose produced in such way is then converted to glucose by other enzymes. The genetic condition lactose intolerance, an inability of the human digestive system to hydrolyze lactose.

15. α-lactose can be named as 4-O-(β-D-galactopyranosido)-α-D-glucopyranose, β-lactose – 4-O-(β-D-galactopyranosido)-β-D-glucopyranose. Arrangement in space is similar to cellobiose:

16. Sucrose can be named as 2-O-(α-D-glucopyranosido)-β-D-fructofuranose.

17. Sucrose, unlike maltose, cellobiose, and lactose, is а non-reducing sugar. No helmiacetal or hemiketal center is present in the molecule, because the glycosidic linkage involves the reducing ends of both monosaccharides. Sucrose, in the solid state and in solution, exists in only one form - there are no  and  isomers, and an open-chain form is not possible. Sucrose, the enzyme needed to break the ,(1 - 2) linkage in sucrose, is present in the human body. Hence sucrose is an easily digested substance.

18. dextrorotatory laevorotatory

19. Linear and branched structure of polysaccharides

20. Homopolysaccharides Structure, composition and properties ofcellulose. Cellulose is the most abundant polysaccharide. It is the structural component of the cell walls of plants. Approximately half of all the carbon atoms in the plant kingdom are contained in cellulose molecules. Structurally, cellulose is а linear (unbranched) D-glucose polymer in which the glucose units are linked by (1-4) glycosidic bonds.

21. At heating with mineral acids cellulose hydrolyzed by the following scheme: In cellulose glucopyranose remainders have linear structure and hydrogen bonds:

22. High-fiber food may also play а role in weight control. Obesity is not seen in parts of the world where people eat large amounts of fiber-rich foods. Many of the weight-loss products on the market are composed of bulk-inducing fibers such as methylcellulose. FIGURE. Cellulose microfibrils. • Some fibers bind lipids such as cholesterol and carry out them of the body with the feces. This lowers blood lipid concentrations and possibly the risk of heart and artery disease.

24. In amylose's structure, the glucose units are connected by (1- 4) glycosidic linkages. Starch (amylose) The number of glucose units present in an amylose chain depends on the source of the starch; 200 – 350 monomer units are usually present. Amylopectin, the other polysaccharide in starch, is similar to amylose, but has а high degree branched structure in the polymer. А one branch link containe 20-25 glucose units. The number of glucose units present in an amylopectin chain consists of 1000 and more units. The branch points involve (1 – 6) linkages: Starch (amylopectin)

25. Glycogen is an ideal storage form for glucose. The large size of these macromolecules prevents them from diffusing out of cells. Also, conversion of glucose to glycogen reduces osmotic pressure. Cells would burst because of increased osmotic pressure if all of the glucose in glycogen were present in cells in free form. High concentrations of glycogen in а cell sometimes cases precipitate or crystallize into glycogen granules. These granules are discernible in photographs of cells under electron microscope magnification. The glucose polymers amylose, amylopectin, and glycogen compare as follows in molecular size and degree of branching: • Amylose: Up to 1000 glucose units; no branching • Amylopectin: Up to 100,000 glucose units; branch points every 20-25 glucose units • Glycogen: Up to 1,000,000 glucose units; branch points every 8-12 glucose units

26. Because of the branching, amylopectin has а larger average molecular mass than the linear amylose. The average molecular mass of amylose is 40000 or more; it is 1-6 mln. for amylopectin. Note that all of the glycosidic linkages in starch (both amylose and amylopectin) are of the -type. In amylose, they are all (1 - 4); in amylopectin, both (1 -4) and (1 -6) linkages are present. Because а linkages can be broken through hydrolysis within the human digestive tract (with the help of the enzyme amylase), starch has nutritional value for humans. The starches present in potatoes and cereal grains (wheat, rice, corn, etc.) account for approximately two-thirds of the world' s food consumption. Fermentayion hydrolysis of starch is shown below:

27. FIGURE. Structure of amylopectine (а), glycogen (b)

28. Dextranes • Dextraneshave bacterial origin, contain remainders of α-D-glucopyranose. Dextranes obtain from sucrose at the present of bacterium (Leuconostocmesenteroides). The main type of bond is α-1,6-glycosidic bond, in place of branching – α-1,4- and α-1,3-glycosidic bonds. The average molecular mass of dextranes is few millions. Partly hydrolyzed dextranes (m. m. – 40000-800000) use in pharmacy as plasmasubstitute (“Polyglucin”, “Reopolyglucin”).

29. Inuline • Inuline – reserve polysaccharide, present in plants. Inuline has linear structure and consists of remainders of β-D-fructofuranose, joined by 2,1-glycosidic bonds, in the end of inuline is α-D-glucopyranose remainder (like sucrose). Molecular mass of inuline is up to 6000. Use for obtaining of D-fructose.

30. Pectin compounds • Pectin compounds (pectins) – polysaccharides consist of polygalacturonic acid, which contain remainders of α-D-galacturonic acid joined by 1,4-glycosidic bonds. Part of carboxyl grups present in appearance of methyl ether. Water solutions of pectins form stable gels. Pectins have antiulcer properties.

31. It is а highly viscous substance and has а molecular weight in several hundred millions. Hyaluronic acid is а principal component of the ground substance of connective tissue. Among other places it is found in skin, synovial fluid, vitreous hemour of the eye, and umbilical cord. It exercises а cementing function in the tissues and capillary walls, and forms а coating gel round the ovum. It accounts for about 80% of the viscosity of synovial fluid which contains about 0. 02 – 0.05% of hyaluronate. Repeat part of hyaluronic acid is D-glucuronic acid and N-acetyl-D-glucosamine joined by β-1,3-glycosidic bond, between disaccharide fragments – β-1,4. Molecular mass of hyaluronic acid is from 1600 to 6400. (1,4)-O--D-Glucopyranosyluronic acid-(1,3)-2-acetamino-2-dezoxy--D-glucopyranose.

32. Chondroitin sulfate. It has similar structure as hyaluronic acid with the difference that the N-acetyl-D-glucosamine unit of the molecule is replaced by N-acetyl-D-galactosamine unit with sulphate group. Repeat part of chondroitin sulphate is D-glucuronic acid and N-acetyl-D-galactosamine which contains sulfate group. Inside of disaccharide fragment is β-1,3-glycosidic bond; between fragments – β-1,4. Sulfate group forms ether bond with hydroxyl group of N-acetyl-D-galactosamine in location 4 (chondroitin-4-sulfate) or in location 6 (chondroitin-6-sulfate). Chondroitin sulfates are found in cartilage, bone, heart valves, tendons and cornea. (1,4)-O--D-Glucopyranosyluronic acid-(1,3)-2-acetamino-2-dezoxy-6-O-sulfo--D-galactopyranose.

33. Hydrocarbon chains of chondroitin-4-sulfate contain up to 150 disaccharides remainders, joined in organism by O-glycosidic bonds with hydroxyl groups of aminoacid remainders.

34. Dermatan sulfate. (Varying amounts of D-glucuronic acid may be present. Concentration increases during aging process.) (1,4)-O--L-idopyranosyluronic acid-(1,3)-2-acetamino-2-dezoxy-4-O-sulfo--D-galactopyranose.

35. Heparin. It is naturally occurring anticoagulant found mainly in the liver, and also in lung, spleen, kidney and intestinal mucosa. It prevents blood clotting by inhibiting the prothrombin-thrombin conversion and thus eliminating the thrombin effect on fibrinogen. Repeat part of heparin consists of D-glucosamin and uronic acid, joined by α-1,4-glycosidic bonds. As uronic acid in heparin present L-iduronic acid or, very rare, D-glucuronic acid. Remainders of glucosamine and L-iduronic acid partly sulfonated.Molecular mass of heparin is 16000-20000. (1,4)-O--D-idupyranosyluronic acid-2-O-sulfo-(1,4)-2-sulfamino-2-dezoxy-6-O-sulfo--D-glucopyranose

36. Fig. Proteoglycan structure

37. Mucin-type carbohydrate While all N-linked oligosaccharides are bound to protein via GlcNAc-Asn, the linking groups of O-glycosidic oligosaccharides are of several types. The most common of these is GalNAc-Ser (or GalNAc-Thr). Considerable mucin-type carbohydrate unit is disaccharide such as Gal-1,3-GalNAc, found in the antifreeze glycoprotein of antarctic fish (Figure), to the complex oligosaccharides of blood groups such as those of the ABO system. Fig. Antifreeze glycoprotein structure.

38. 6. Lipids Lipidsdifferfromtheotherclassesofnaturallyoccurringbiomolecules (carbohydrates,proteins, andnucleicacids), theyaremoresolubleinnon- or weaklypolarsolvents (diethylether, hexane, dichloromethane) thaninwater. Theyincludeavarietyofstructuraltypes, acollectionofwhichisintroducedinthischapter.Inspiteofthenumberofdifferentstructuraltypes, lipidsshareacommonbiosyntheticorigininthattheyareultimatelyderivedfromglucose. Duringonestageofcarbohydratemetabolism, calledglycolysis, glucoseisconvertedtolacticacid. Pyruvicacidisanintermediate product.

39. Classification of lipids

40. Lipids are organic compounds, found in living organisms, that are soluble in nonpolar organic solvents. Because compounds are classified as lipids on the basis of a physical property— their solubility in an organic solvent—rather than as a result of their structures, lipids have a variety of structures and functions, as the following examples illustrate:

42. Fats and oils are naturally occurring mixtures of triacylglycerols, also called triglycerides.They differ in that fats are solids at room temperature and oils are liquids. Wegenerally ignore this distinction and refer to both groups as fats. Triacylglycerols are built on a glycerol framework. Simple triacylglycerines include similar fatty acids , mixed – different. All three acyl groups in a triacylglycerol may be the same, all three may be different,or one may be different from the other two.

44. Nomenclature, methods of getting of fats For simple glycerides the name is made up of the name of the alcohol (glycerol) or its radical (glyceryl) and the name of the acid; or the name of the acid concerned is changed to suffix in. For mixed glycerides, the position and names of the acid groups are specified by Greek letters α, β, α’ or by the numerals 1, 2 and 3. • Methods of getting: • O-acylation of alcohols; • Allocation from plants: melting out, pressing or extraction by organic solvents.

45. The most widespread fatty acids in natural oils and fats:

46. Double bonds are rigid structures, unsaturared acid molecules that contain them can occur in two isomeric forms: cis and trans. In cis-isomers, for example, similar or identical groups are on the same side of double bond (a). When such groups are on opposite sides of a double bond, the molecule is said to be a trans-isomer (b): The double bonds in unsaturated fatty acids generally have the cis configuration. This configuration produces a bend in the molecules, which prevents them from packing together as tightly as fully saturated fatty acids. As a result, unsaturated fatty acids have fewer intermolecular interactions and, therefore, lower melting points than saturated fatty acids with comparable molecular weights . The melting points of the unsaturated fatty acids decrease as the number of double bonds increases. For example, an 18-carbon fatty acid melts at 69 °C if it is saturated, at 13 °C if it has one double bond, at if it has two -5 °C o double bonds, and at -11 °C if it has three double bonds.

47. Triacylglycerols that are solids or semisolids at room temperature are called fats. Fats are usually obtained from animals and are composed largely of triacylglycerols with either saturated fatty acids or fatty acids with only one double bond. The saturated fatty acid tails pack closely together, giving the triacylglycerols relatively high melting points, causing them to be solids at room temperature. Liquid triacylglycerols are called oils. Oils typically come from plant products such as corn, soybeans, olives, and peanuts. They are composed primarily of triacylglycerols with unsaturated fatty acids that cannot pack tightly together. Consequently, they have relatively low melting points, causing them to be liquids at room temperature.

48. Hydrolysis of а triacylglycerol Hydrolysis of а triacylglycerol is the reverse of the esterification reaction by which it wet formed. Complete hydrolysis of а triacylglycerol molecule always gives one glycerol molecule and three fatty acid molecules as products.

49. 7. Chemical properties of fats 1). Hydrolysis of fats with alkali (e.g., sodium hydroxide) yields salts of thefatty acids, and those of the alkali metals, such as sodium or potassium, are useig as soaps. Another name of this reaction – “saponification”: The solubility of lipids in nonpolar organic solvents results from their significant hydrocarbon component. The hydrocarbon portion of the compound is responsible for its “oiliness” or “fattiness.” The word lipid comes from the Greek lipos, which means “fat.”

50. 2). Oxidation of fates. Oxidation cases rancidity of fates. During oxidation form aldehydes with short carbon chain. Oxidation at the soft conditions (water solution of KMnO4) cases formation of glycols. At the rigid conditions carbon skeleton destroys with formation of remainders of carbonic acids with shorter carbon chains.