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20 20-1 2006 Thomson Learning, Inc. All rights reserved Chapter 20, actually (CHPT 19) Carbohydrates Carbohydrates Slide 2 20 20-2 2006 Thomson Learning, Inc. All rights reserved Carbohydrates Carbohydrate: Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis. Most simple carbos = Saccharides e.g. monosaccharides,, oligosaccharides, polysachrides, dep. On # of simple sugars attached Monosaccharide: Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate. Slide 3 20 20-3 2006 Thomson Learning, Inc. All rights reserved Monosaccharides C n H 2n O n ngeneral formula C n H 2n O n, where n varies from 3 to 8. Two Types: Aldose: Aldose: a monosaccharide containing an aldehyde group. Ketose: Ketose: a monosaccharide containing a ketone group. C 6 H 12 O 6 Slide 4 20 20-4 2006 Thomson Learning, Inc. All rights reserved classified by their number of carbon atoms. Monosaccharides Slide 5 20 20-5 2006 Thomson Learning, Inc. All rights reserved Monosaccharides There are only two trioses: Often aldo- and keto- are omitted compounds are referred to simply as trioses. Although triose does not tell the nature of the carbonyl group, it at least tells the number of carbons. Slide 6 20 20-6 2006 Thomson Learning, Inc. All rights reserved Monosaccharides Glyceraldehyde, the simplest aldose, contains a stereocenter and exists as a pair of enantiomers. Fig 19.1 Slide 7 20 20-7 2006 Thomson Learning, Inc. All rights reserved Monosaccharides R R Horizontal lines represent bonds projecting forward from the stereocenter. Vertical lines represent bonds projecting to the rear. Only the stereocenter is in the plane. Fischer projection: Fischer projection: a two dimensional representation showing the configuration of stereocenters. 2,3 hydroxy propanal Slide 8 20 20-8 2006 Thomson Learning, Inc. All rights reserved D,L Monosaccharides 1891, E. Fischer arbitrary assignments D/L to the enantiomers of glyceraldehyde. NOTE: R = D L = S (R) (S) D-monosaccharide:D-monosaccharide: the -OH on penultimate carbon on right L-monosaccharide:L-monosaccharide: the -OH on penultimate carbon on left in a Fischer projection. Dextrorotatorylevatory Slide 9 20 20-9 2006 Thomson Learning, Inc. All rights reserved Suffix ose indicates compound = carbo D,L Monosaccharides Nature predominately makes the D form as well D amino acids discussed later The most common D-tetroses and D-pentoses are: Note: D,L specifies configuration @ stereocenter farthest from Carbonyl Slide 10 20 20-10 2006 Thomson Learning, Inc. All rights reserved D,L Monosaccharides The three most common D-hexoses are: aka blood sugar Human blood~65-110 mg glucose/100ml blood I.V. bags contain 5% glucose solut. Slide 11 20 20-11 2006 Thomson Learning, Inc. All rights reserved Amino Sugars Amino sugars: Have -NH 2 group in place of an -OH group. Only three amino sugars are common in nature: D-glucosamine, D-mannosamine, and D-galactosamine Slide 12 20 20-12 2006 Thomson Learning, Inc. All rights reserved Amino Sugars Slide 13 20 20-13 2006 Thomson Learning, Inc. All rights reserved Cyclic Structure of monosaccharides RECALL: 17.7 hemiacetals Aldehydes and ketones react with alcohols to form hemiacetals. From one stereocenter (aldehyde/alcohol) to two (hemiacetal) Slide 14 20 20-14 2006 Thomson Learning, Inc. All rights reserved Haworth Projections D-Glucose forms these cyclic hemiacetals. New stereogenic center = anomeric carbon Slide 15 20 20-15 2006 Thomson Learning, Inc. All rights reserved Haworth Projections In the terminology of carbohydrate chemistry, anomers Stereoisomers that differ in configuration only at anomeric carbon are called anomers pyranose six-membered hemiacetal ring :pyranose, furanose five-membered hemiacetal ring: furanose. means -OH on anomeric carbon is on side of the ring opposite from the terminal -CH2OH. means -OH on anomeric carbon same side of ring as the terminal -CH2OH. Slide 16 20 20-16 2006 Thomson Learning, Inc. All rights reserved Haworth Projections Aldopentoses also form cyclic hemiacetals. The most prevalent forms of D-ribose/ other pentoses are furanoses. The prefix deoxy means without oxygen. Slide 17 20 20-17 2006 Thomson Learning, Inc. All rights reserved Haworth Projections D-Fructose (a 2-ketohexose) also forms a five- membered cyclic hemiacetal. Where is the anomeric carbon? Slide 18 20 20-18 2006 Thomson Learning, Inc. All rights reserved Chair Conformations >> Haworth projected chair conformation For pyranoses, the six-membered ring is more accurately represented as a chair conformation. The above are in equilib. In aqueous solut. Most common form b/c OH in equatorial vs axial (more stable) Slide 19 20 20-19 2006 Thomson Learning, Inc. All rights reserved Chair Conformations In both Haworth projections and chair conformations, the orientations of groups on carbons 1- 5 of -D- glucopyranose are up, down, up, down, and up. Slide 20 20 20-20 2006 Thomson Learning, Inc. All rights reserved Mutarotation e.g : -D-glucose or -D-glucose into H2O... specific rotation of solution changes to an equilibrium of +52.7(64% beta & 36% alpha forms). change in mea. specific rotation that accompanies the equilibration of alpha and beta anomers in aqueous solution. Slide 21 20 20-21 2006 Thomson Learning, Inc. All rights reserved Physical Properties Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol Sweetness relative to sucrose: Slide 22 20 20-22 2006 Thomson Learning, Inc. All rights reserved Formation of Glycosides Treatment of a monosaccharide, all of which exist almost exclusively in cyclic hemiacetal forms, with an alcohol gives an acetal. Slide 23 20 20-23 2006 Thomson Learning, Inc. All rights reserved Formation of Glycosides glycosideA cyclic acetal derived from a monosaccharide is called a glycoside. glycosidic bondThe bond from the anomeric carbon to the -OR group is called a glycosidic bond. Mutarotation is not possible in a glycoside because an acetal, unlike a hemiacetal, is not in equilibrium with the open-chain carbonyl-containing compound. Glycosides are stable in water and aqueous base, but like other acetals, are hydrolyzed in aqueous acid to an alcohol and a monosaccharide. e-ideGlycosides are named by listing the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate in which the ending -e is replaced by -ide. Slide 24 20 20-24 2006 Thomson Learning, Inc. All rights reserved Reduction to Alditols The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH 4 and H 2 in the presence of a transition metal catalyst. alditolThe reduction product is called an alditol. Slide 25 20 20-25 2006 Thomson Learning, Inc. All rights reserved Reduction to Alditols Sorbitol is found in the plant world in many berries and in cherries, plums, pears, apples, seaweed, and algae. It is about 60 percent as sweet as sucrose (table sugar) and is used in the manufacture of candies and as a sugar substitute for diabetics. These three alditols are also common in the biological world. Slide 26 20 20-26 2006 Thomson Learning, Inc. All rights reserved Oxidation to Aldonic Acids The aldehyde group of an aldose is oxidized under basic conditions to a carboxylate anion. aldonic acidThe oxidation product is called an aldonic acid. reducing sugarA carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing sugar (it reduces the oxidizing agent). Slide 27 20 20-27 2006 Thomson Learning, Inc. All rights reserved Oxidation to Uronic Acids uronic acid Enzyme-catalyzed oxidation of the primary alcohol at C-6 of a hexose yields a uronic acid. Enzyme-catalyzed oxidation of D-glucose, for example, yields D-glucuronic acid. Slide 28 20 20-28 2006 Thomson Learning, Inc. All rights reserved D-Glucuronic Acid D-Glucuronic acid is widely distributed in the plant and animal world. In humans, it is an important component of the acidic polysaccharides of connective tissues. It is used by the body to detoxify foreign phenols and alcohols; in the liver, these compounds are converted to glycosides of glucuronic acid and excreted in the urine. Slide 29 20 20-29 2006 Thomson Learning, Inc. All rights reserved Phosphate Esters Mono- and diphosphoric esters are intermediates in the metabolism of monosaccharides. For example, the first step in glycolysis is conversion of D-glucose to -D-glucose 6-phosphate. Note that at the pH of cellular and intercellular fluids, both acidic protons of a diphosphoric ester are ionized, giving it a charge of -2. Slide 30 20 20-30 2006 Thomson Learning, Inc. All rights reserved Disaccharides Sucrose (table sugar) Sucrose is the most abundant disaccharide in the biological world; it is obtained principally from the juice of sugar cane and sugar beets. Sucrose is a nonreducing sugar. Slide 31 20 20-31 2006 Thomson Learning, Inc. All rights reserved Disaccharides Lactose Lactose is the principal sugar present in milk; it makes up about 5 to 8 percent of human milk and 4 to 6 percent of cow's milk. It consists of D-galactopyranose bonded by a -1,4- glycosidic bond to carbon 4 of D-glucopyranose. Lactose is a reducing sugar. Slide 32 20 20-32 2006 Thomson Learning, Inc. All rights reserved Disaccharides Maltose Present in malt, the juice from sprouted barley and other cereal grains. Maltose consists of two units of D-glucopyranose joined by an -1,4-glycosidic bond. Maltose is a reducing sugar. Slide 33 20 20-33 2006 Thomson Learning, Inc. All rights reserved Polysaccharides Polysaccharide: Polysaccharide: a carbohydrate consisting of large numbers of monosaccharide units joined by glycosidic bonds. Starch: Starch: a polymer of D-glucose. Starch can be separated into amylose and amylopectin. Amylose is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds. Amylopectin contains chains up to 10,000 D-glucose units also joined by -1,4-glycosidic bonds; at branch points, new chains of 24 to 30 units are started by - 1,6-glycosidic bonds. Slide 34 20 20-34 2006 Thomson Learning, Inc. All rights reserved Polysaccharides Figure 20.3 Amylopectin. Slide 35 20 20-35 2006 Thomson Learning, Inc. All rights reserved Polysaccharides Glycogen Glycogen is the energy-reserve carbohydrate for animals. Glycogen is a branched polysaccharide of approximately 10 6 glucose units joined by -1,4- and - 1,6-glycosidic bonds. The total amount of glycogen in the body of a well- nourished adult human is about 350 g, divided almost equally between liver and muscle. Slide 36 20 20-36 2006 Thomson Learning, Inc. All rights reserved Polysaccharides Cellulose Cellulose is a linear polysaccharide of D-glucose units joined by -1,4-glycosidic bonds. It has an average molecular weight of 400,000 g/mol, corresponding to approximately 2200 glucose units per molecule. Cellulose molecules act like stiff rods and align themselves side by side into well-organized water- insoluble fibers in which the OH groups form numerous intermolecular hydrogen bonds. This arrangement of parallel chains in bundles gives cellulose fibers their high mechanical strength. It is also the reason why cellulose is insoluble in water. Slide 37 20 20-37 2006 Thomson Learning, Inc. All rights reserved Polysaccharides Figure 20.4 Cellulose is a linear polymer containing as many as 3000 units of D-glucose joined by -1,4-glycosidic bonds. Slide 38 20 20-38 2006 Thomson Learning, Inc. All rights reserved Polysaccharides Cellulose (contd) Humans and other animals cannot use cellulose as food because our digestive systems do not contain - glucosidases, enzymes that catalyze hydrolysis of - glucosidic bonds. Instead, we have only -glucosidases; hence, the polysaccharides we use as sources of glucose are starch and glycogen. Many bacteria and microorganisms have - glucosidases and can digest cellulose. Termites have such bacteria in their intestines and can use wood as their principal food. Ruminants (cud-chewing animals) and horses can also digest grasses and hay. Slide 39 20 20-39 2006 Thomson Learning, Inc. All rights reserved Acidic Polysaccharides Acidic polysaccharides: Acidic polysaccharides: a group of polysaccharides that contain carboxyl groups and/or sulfuric ester groups, and play important roles in the structure and function of connective tissues. There is no single general type of connective tissue. Rather, there are a large number of highly specialized forms, such as cartilage, bone, synovial fluid, skin, tendons, blood vessels, intervertebral disks, and cornea. Most connective tissues are made up of collagen, a structural protein, in combination with a variety of acidic polysaccharides. Slide 40 20 20-40 2006 Thomson Learning, Inc. All rights reserved Acidic Polysaccharides Hyaluronic acid Hyaluronic acid contains from 300 to 100,000 repeating units. is most abundant in embryonic tissues and in specialized connective tissues such as synovial fluid, the lubricant of joints in the body, and the vitreous of the eye where it provides a clear, elastic gel that maintains the retina in its proper position Slide 41 20 20-41 2006 Thomson Learning, Inc. All rights reserved Acidic Polysaccharides Heparin Heparin: a heterogeneous mixture of variably sulfonated polysaccharide chains, ranging in molecular weight from 6,000 to 30,000 g/mol. Slide 42 20 20-42 2006 Thomson Learning, Inc. All rights reserved Acidic Polysaccharides Heparin (contd) Heparin is synthesized and stored in mast cells of various tissues, particularly the liver, lungs, and gut. The best known and understood of its biological functions is its anticoagulant activity. It binds strongly to antithrombin III, a plasma protein involved in terminating the clotting process. Slide 43 20 20-43 2006 Thomson Learning, Inc. All rights reserved End Chapter 20 Carbohydrates