Carbohydrate Chemistry Lec. 2 PDF

South Valley National University Faculty of Pharmacy Biochemistry Department Carbohydrate Chemistry Lec. 2 Dr/ Shimaa Abd El-Nasser Lecturer of Biochemistry  Disaccharides The monosaccharides within them are linked by a...

South Valley National University Faculty of Pharmacy Biochemistry Department Carbohydrate Chemistry Lec. 2 Dr/ Shimaa Abd El-Nasser Lecturer of Biochemistry  Disaccharides The monosaccharides within them are linked by a glycosidic bond (-O- glycosidic linkage), the position of which may be designated α- or β- or a combination of the two (α-,β-). Glycosidic bonds are cleaved by enzymes known as glycosidases.  Disaccharides The three major disaccharides are sucrose, lactose, and maltose. Classification: They can be either reducing or non- reducing, depending on the presence of a free carbonyl group.  Disaccharides Maltose Isomaltose Lactose Sucrose Other name Malt sugar Milk sugar Table sugar Cane and beet sugar Subunits 2 -glucose 2 -glucose -galactose and  or β- -glucose glucose linked to - fructose Glycosidic link -1, 4. -1, 6 -1,4- -1,-2 Sources -Malt -Digestion of -Milk -Cane and beet -Digestion of starch and -It may appear in urine starch and glycogen by in late pregnancy and glycogen by amylase during lactation amylase  Disaccharides Lactose is the most suitable sugar for baby feeding because: – It is least sweet sugar, so the baby can take large amounts without loss of his appetite. – Non-fermentable due to absence of lactase enzyme in the yeast, so no gas formation and not cause colic or distension. – Has laxative effect, preventing constipation, no irritation to stomach so no vomiting. – Easily digestible and help the absorption of minerals present in milk. – Unabsorbed sugar used as food for the large intestinal bacteria that form number of vitamins that benefits the baby.  Polysaccharides Polysaccharides contain hundreds or thousands of carbohydrate units. Polysaccharides are not reducing sugars, since the anomeric carbons are connected through glycosidic linkages. Nomenclature: Homopolysaccharide: a polysaccharide is made up of one type of monosaccharide unit. Heteropolysaccharide: a polysaccharide is made up of more than one type of monosaccharide unit.  Homopolysaccharides Starch Starch is a polymer consisting of D-glucose units. Starch (and other glucose polymers) are usually insoluble in water because of the high molecular weight, but they can form thick colloidal suspensions with water. Starch is a storage compound in plants, and made of glucose units It is a homopolysaccharide made up of two components: amylose and amylopectin. Most starch is 10-30% amylose and 70-90% amylopectin.  Amylose: a straight chain structure formed by 1,4 glycosidic bonds between α-D-glucose molecules. This causes the blue colour change on reaction with iodine. Amylose is poorly soluble in water, but forms micellar suspensions Amylopectin: a glucose polymer with mainly α -(1→4) linkages, but it also has branches formed by α -(1→6) linkages. Branches are generally longer than shown above. Amylopectin causes a red-violet colour change on reaction with iodine. This change is usually masked by the much darker reaction of amylose to iodine.  Homopolysaccharides Glycogen Storage polysaccharide in animals Glycogen constitutes up to 10% of liver mass and 1-2% of muscle mass Glycogen is stored energy for the organism Similar in structure to amylopectin, only difference from starch: number of branches. Alpha(1,6) branches every 8-12 residues Like amylopectin, glycogen gives a red-violet color with iodine.  Homopolysaccharides Cellulose The β-glucose molecules are joined by condensation, i.e. the removal of water, forming β-(1,4) glycosidic linkages. The glucose units are linked into straight chains each 100-1000 units long. Weak hydrogen bonds form between parallel chains binding them into cellulose microfibrils. Cellulose microfibrils arrange themselves into thicker bundles called cellulose fibres. The cellulose fibres are often “glued” together by other compounds such as hemicelluloses and calcium pectate to form complex structures such as plant cell walls.  Because of the β-linkages, cellulose has a different overall shape from amylose, forming extended straight chains which hydrogen bond to each other, resulting in a very rigid structure. Cellulose is an important structural polysaccharide, and is the single most abundant organic compound on earth. It is the material in plant cell walls that provides strength and rigidity; wood is 50% cellulose. Most animals lack the enzymes needed to digest cellulose, although it does provide needed roughage (dietary fiber) to stimulate contraction of the intestines and thus help pass food along through the digestive system  Some animals, such as cows, sheep, and horses, can process cellulose through the use of colonies of bacteria in the digestive system which are capable of breaking cellulose down to glucose; ruminants use a series of stomachs to allow cellulose a longer time to digest. Some other animals such as rabbits reprocess digested food to allow more time for the breakdown of cellulose to occur. Cellulose is also important industrially, from its presence in wood, paper, cotton, cellophane, rayon, linen, nitrocellulose (guncotton), photographic films (cellulose acetate), etc.  Homopolysaccharides Chitin Chitin is a polymer that can be found in anything from the shells of beetlesto webs of spiders. It is present all around us, in plant and animal creatures. It is sometimes considered to be a spinoff of cellulose, because the two are very molecularly similar. Cellulose contains a hydroxy group, and chitin contains acetamide. Chitin is unusual because it is a "natural polymer," or a combination of elements that exists naturally on earth. Chitin is a very firm material, and it help protect an insect against harm and pressure.  Homopolysaccharides Inulin Inulin is stored in the tubers. It is also found in onion and garlic. Inulin has a molecular weight of about 5,000 and consists of about 30–35 fructose units per molecule. It is formed in the plants by eliminating a molecule of water from the glycosidic OH group on carbon atom 2 of one group on carbon atom 1 of the adjacent.  Homopolysaccharides Pectin Pectins are found as intercellular substances in the tissues of young plants and are especially abundant in ripe fruits such as guava, apples and pears. Pectins is a polysaccharide of α-D-galacturonic acid where some of the free carboxyl groups are, either partly or completely, esterified with methyl alcohol and others are combined with calcium or magnesium ions. Chemically, they are called polygalacturonides  Mucopolysaccharides Polysaccharides that are composed not only of a mixture of simple sugars but also of derivatives of sugars such as amino sugars and uronic sugars are called mucopolysaccharides.  Mucopolysaccharides Hyaluronic acid It is the most abundant member of mucopolysaccharides and is found in higher animals as a component of various tissues such as the vitreous body of the eye, the umbilical cord and the synovial fluid of joints. It is a straight-chain polymer of D-glucuronic acid and N-acetyl- D- glucosamine (NAG) alternating in the chain. Its molecular weight approaches approximately, 5,000,000. linkages invloved, β-1 → 3 and β-1 → 4.  Mucopolysaccharides Chondroitin Chondroitin is of limited distribution. It is found in cartilage and is also a component of cell coats. It is a parent substance for two more widely distributed mucopolysaccharides, chondroitin sulfate A and chondroitin sulfate B. Chondroitin is similar in structure to hyaluronic acid except that it contains galactosamine rather than glucosamine. It is, thus, a polymer of β-D-glucuronic- 1, 3- N-acetyl-D-galactosamine joined by β- 1 → 4 linkages.  The two chondroitin sulfate A and C are widely distributed and form major structural components of cartilage, tendons and bones. Chondroitin sulfates may be regarded as derivatives of chondroitin where, in the galactosamine moiety, a sulfate group is esterified either at carbon 4 as in chondroitin sulfate A or at carbon 6 as in chondroitin sulfate C The two linkages involved in both types of chondroitin sulfate would, obviously, be the same. These are β-1 → 3 and β-1 → 4.  Mucopolysaccharides Dermatan Sulfate Dermatan sulfate is a mucopolysaccharide structurally similar to chondroitin sulfate A except that the D-glucuronic acid is replaced by L-iduronic acid The two linkages involved are α-1 → 3 and β-1 → 4. Dermatan sulfate is also known by its conventional name, chondroitin sulfate B.  Mucopolysaccharides Keratosulfate Keratosulfate differs from other mucopolysaccharides in that the uronic acid component is replaced by D-galactose. Here, the second acetylated amino sugar component (which is N-acetyl-D-glucosamine in this case) is esterified by a sulfate group at carbon 6. Although, the two alternating linkages involved are β-1 → 4 and β-1 → 3, in this case the linkage between the repeating disaccharide units is β-1 →3 rather than β-1 → 4.  Mucopolysaccharides Heparin Heparin is composed by disaccharide units containing one uronic acid (l-iduronic acid, or d-glucuronic acid) and one amino sugar (d-glucosamine). Heparin is a naturally occurring anticoagulant that prevents the formation and extension of blood clots. Heparin does not break down clots that have already formed (unlike tissue plasminogen activator) but allows fibrinolysis to work normally to break down clots.