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Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of and their Structures Name of the Content Writer: Dr. S. Sumathi

Quadrant – I 10.2.1. Introduction Carbohydrates are the major constituents in most fruits, vegetables, legumes, and cereal grains, and do provide texture and flavor in many processed foods. Carbohydrates are the major energy source for humans by digestion and absorption in the small intestine and, to a lesser extent, by microbial fermentation in the large intestine. Available and unavailable carbohydrates are the two classifications of food carbohydrates. Available carbohydrates are those that are hydrolyzed by enzymes of the human gastrointestinal tract to . These monosaccharides are absorbed in the small intestine and enter the pathways of metabolism. Unavailable carbohydrates are not hydrolyzed by human digestive enzymes, but they may be partially or totally fermented by bacteria in the large intestine, forming short-chain fatty acids that may be absorbed and contribute to the body’s energy needs. The carbohydrates are hydrophilic in nature and forms various derivatives.. Carbohydrates are also covalently bound to many proteins and lipids to form a class called as glycoconjugates that includes glycoproteins, proteoglycans, and glycolipids . OBJECTIVES 1.To outline the classification of different classes of carbohydrates 2.To outline the structure of various types of carbohydrates 3. The enumerate the role of these classes in the microbes, plants and animals

10.3 MONOSACCHARIDES – STRUCTURAL ASPECTS Monosaccharides or simple include the such as and such as . Aldoses contain one aldehyde group and hence are polyhydroxy aldehydes. Ketoses contain one ketone group and hence are polyhydoxy ketones. Both have the empirical chemical formula (CH 2 O) n.

Important character of monosaccharides is Stereoisomerism. Stereoisomers are the compounds that have the same structural formulae but differ in their spatial configuration. An asymmetric carbon atom (chiral carbon) is a carbon atom that is attached to four different types of atoms or

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi four different groups of atoms. Stereoisomers can be further separated into the two categories of and enantiomers. One type of diastereomers (or geometric stereoisomers) differ by "cis" and "trans" orientations.

Enantiomers are a class of stereoisomers related like an object and its mirror image. Enantiomers differ in their "handedness" as the left hand and right hand are related. They are a pair of mirror image molecules that cannot be superimposed on each other. The number of possible stereoisomers depends upon the number of chiral centers in the molecule. Van'tHoffs rule states: number of stereoisomers = 2n , where n = number of chiral centers. For example, a molecule with 2 chiral centers can have 4 stereoisomers. –is the reference carbohydrate. Glyceraldehyde is the simplest with one asymmetric carbon atom. There are two forms- The d / l system is commonly used for designating the chirality of sugars and amino acids and has been chosen as the reference carbohydrate to represent the structure of all other classes of carbohydrates. Thus, the three- carbon glyceraldehyde exists as both d -and l -enantiomers. The two-carbon aldehyde, does not have a chiral carbon atom and hence has no optical activity. All d - aldoses are related to d - glyceraldehyde, and l -aldoses are similarly related to l -glyceraldehyde. The relation of d -aldoses to d -glyceraldehyde can be seen clearly by looking at a scheme for the chemical synthesis of the series of d -aldoses from d -glyceraldehyde.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

D and L isomers For sugars with more than one chiral center, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto group.

Most naturally occurring sugars are D isomers.

D& L sugars are mirror images of one another. They have the same name. For example, D-

glucose and L-glucose are shown at right.

Other stereoisomers have unique names, e.g., glucose, , , etc. The number of

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi stereoisomer is 2 n, where n is the number of asymmetric centers. Thus the six-carbon aldoses that have 4 asymmetric centers, have 16 stereoisomers (8 D-sugars and 8 L-sugars).

Optical activity of sugars Optical activity is a characteristic feature of compounds with asymmetric carbon atom. When a beam of polarized light is passed through a solution of an optical isomer,it will be rotated either to the right or left. The term detrorotatory(+) and levoraotatory (-) are used to refer to compounds that respectively rotate the plane polarized light to the right or left. An optical isomer may be designated as D(+),D(-),L(+) and L(-) based on its structural relation with glyceraldehyde. Thus the D and L configurations are based on the structure of and their optical activities may be different. Racemic mixture: If the D and L isomers are present in equal concentration, it is known as racemic mixture or DL mixture. Racemic mixture does not exhibit any optical activity because the dextro and levorotatory activities cancel each other. Configuration of D aldoses The configuration of the possible D aldoses starting from D glyceraldehydes is by Kiliani fischer synthesis, by increasing the chain length of an , by one carbon at a time. Thus starting with an aldotriose(3C), aldotetrose(4C), aldopentose(5C) and aldohexose (6C) are formed. Among the various aldohexose glucose,mannose and galactose are most common. And among these D glucose is the only aldohexose that predominantly occurs in nature.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Configuration of D –Ketoses Dihydroxy acetone is the starting material for the synthesis of sugars. D , D ,D Fructose and D- are physiologically important.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

ALDOSES

D- D- D- D-glucose D-galactose D-mannose

KETOSES

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

D-ribulose D-fructose

Epimers Sugars that vary in their configuration at only one carbon are epimers: for example, d -glucose and d -mannose are C2 epimers, whereas d -glucose and d -galactose are C4 epimers. Enzymes that catalyze epimer formation are called epimerases.

Enantiomers Enantiomers are special type of stereoisomers that are mirror images of each other. The two members are designated as D and L –sugars. Enantiomers of glucose are L glucose and D- Glucose. Majority of the sugars in the higher animals are of D type.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Diastereomers The term diastereomers is used to represent the stereoisomers that are not mirror images of one another.

10.3.2 Structure of Glucose

The aldehyde and ketone moieties of the carbohydrates with five and six carbons will spontaneously react with alcohol groups present in neighbouring carbons to produce intramolecular hemiacetals or hemiketals, respectively. This results in the formation of five- or six-membered rings. Because the five-membered ring structure resembles the organic molecule furan, derivatives with this structure are termed . Those with six-membered rings resemble the organic molecule pyran and are termed .

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Such structures can be depicted by either Fischer or Haworth style diagrams. The numbering of the carbons in carbohydrates proceeds from the carbonyl carbon, for aldoses, or the carbon nearest the carbonyl, for ketoses.

Cyclic Fischer Projection of α-D-Glucose Haworth Projection of α-D-Glucose

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration of C-1 if they are aldoses or in the configuration at C-2 if they are ketoses. The epimeric carbonin anomers are known as anomeric carbon or anomeric center. The alpha and beta cyclic forms of d D Glucose are known as anomers. These anomers differ in certain physical and chemical properties.

Mutarotation:

Is the process of interconversion of α- and β- anomers

 The α- and β- anomers of carbohydrates are typically stable solids.  However, in aqueous solution, they quickly equilibrate to an equilibrium mixture of the two forms.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

 For example, in aqueous solution, glucose exists as a mixture of 36% α- and 64% β- (>99% of the forms exist in solution).  The equilibration occurs via the ring opening of the cyclic sugar at the anomeric center with the acyclic form as the intermediate.

10.3.3 Formation of glycosidic linkages The general term glycoside is used to describe any molecule in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bone. As an example, the acid- catalyzed reaction of a sugar (glucose) with an alcohol (methanol) to form methyl d - glucopyranoside, which is an example of an O -glycoside. Although only the α-glycoside is shown, both α - and β – glycosides form in nonenzymatic reactions. When properly activated, sugars react with each other to form specific and in which a sugar residue is linked by a new bond between its anomeric carbon and one of the hydroxyl groups of the second sugar residue. Thus the sugar residues in oligosaccharides and polysaccharides are linked by O -glycosidic bonds.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

10.3.4 Other classes – alditols The alditols, or polyols, which occur naturally in plants and other organisms, are reduction products of aldoses and ketoses in which the carbonyl has been reduced to an alcohol. Two common alditols are xylitol and sorbitol (glucitol). Reduction of ketoses gives an epimeric pair of alditols unless the reaction is enzyme-catalyzed and therefore stereospecific. The alditols, like the sugars, are soluble in water and vary in degree of sweetness. Xylitol, the sweetest, approaches the sweetness of .

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Glucuronic acids Sugar acids are sugars in which the carbonyl group and/or the terminal − CH 2 OH group has been oxidized to a carboxyl group ( − COOH). Uronic acids are formed when the terminal terminal − CH 2 OH group of an aldose or ketose is oxidized to a terminal carboxyl group ( − COOH). Aldonic acids are oxidation products of the aldoses in which the C1 aldehyde functional group ( − CHO) has been oxidized to a carboxyl group ( − COOH). Aldaric acids are dicarboxylic acids in which both terminal groups of the aldose have been oxidized to carboxyl groups.

Deoxy sugars These are sugars containing one oxygen less than that present in the parent molecule. The groups –CHOH and - CH2OH become – CH2 and CH3 due to the absence of oxygen.2 Deoxy ribose is the most important since it is a structural constituent of DNA. Others include (6-deoxyl -galactose), and (6-deoxy- l -mannose).

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Amino sugars In the common amino sugars, the C2 hydroxyl group is replaced by an amino group. d - glucosamine and d - galactosamine are common amino sugars, which usually occur as the N - acetyl derivatives (N -acetyl- d – glucosamine and N -acetyl- d -galactosamine). They are constituents of and of many glycoproteins.

10.3.5 Glycoproteins Glycoproteins are carbohydrates linked to proteins by two types of covalent bonds a) O- glycosidic bonds using the hydroxyl groups of serine and threonine and b) N- glycosdic bonds using the side chain amide groups of asparagines. Glycoproteins are involved in many biological functions including immunological protection, cell-cell recognition, antifreeze protection and host-pathogen interactions. N acetyl

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

10.4 Disaccharides and oligosaccharides are made up of monosaccharides covalently linked by glycosidic bonds. They can be classified as either reducing or non reducing. A or terminating with a residue that has an unsubstituted anomeric − OH group is reducing. An oligosaccharide that has the final sugar unit joined by linkage of its anomeric carbon to the anomeric carbon of preceding sugar so that the oligosaccharide does not have a free anomeric − OH is nonreducing. Sucrose Sucrose (table sugar), a nonreducing disaccharide, is composed of glucose linked to fructose alpha (1-2) linkage. Sucrose is widely distributed in plants and it is the major carbohydrate found in plants. Sucrose is the most abundant among the naturally occurring sugars. It has distinctive advantage over other sugars as a storage and transport form. Sucrose.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Lactose is made up of Galactose linked to glucose by β -(1- 4 glycosidic linkage. It is known as, milk sugar and is synthesized in the mammary glands of mammals. Lactose is present in dairy products andalso in processed foods that contain whey products formed from the watery part of milk that remains after the manufacture of cheese. It has about one third the sweetness of sucrose.

Trehalose is made up of two units of glucose liked by α (1,1) glycosidic linkage. It is a nonreducing disaccharide found in fungi, such as young mushrooms and yeasts, and in

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi invertebrates, such as insect hemolymph. It is digested by an intestinal tract by α -glucosidase called trehalase. Trehalose is a insignificant disaccharide found in the diet of human.

Maltose occurs naturally in the seeds of -producing plants, and small amounts are used in processed foods. does not occur naturally and is got from the acidic hydrolysis of starch. Maltose can be easily hydrolysed by humans because of the presence of glycosidases that easily hydrolyse α(1-4)glycosidic bonds

10.5 OLIGOSACCHARIDES

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Although disaccharides are common components of the diet, oligosaccharides containing 3 to 10 sugar residues are not abundant. α – Galactosides A series of α -galactosides, known as , , verbascose, and ajucose, occur in relatively large amounts in soybeans, lentils, and other legume seeds.These oligosaccharides contain a sucrose moiety to which one or more residues of α -galactose are attached by a 1,6 linkage to the glucose moiety of sucrose. Raffinose, stachyose, verbascose, and ajucose contain one, two, three,or four residues of α - d -galactose, respectively. The raffinose family oligosaccharides are produced during plant seed development. As humans do not have a digestive α - d -galactosidase, these oligosaccharides pass into the lower gut to be metabolized by the anaerobic bacteria. Excessive flatulence may result from fermentation of these oligosaccharides.

β - Fructose oligosaccharides are produced by hydrolysis of obtained from chicory roots. Inulinis a polymer of fructose residues with the fructose residues present as rings joined by β (2,1)-glycosidic linkages. The partial hydrolysate of inulin (oligofructose) is used as a food ingredient. Fructose oligosaccharidesare about 30% as sweet as sucrose and are used asemulsifiers,bulking agents, fat replacers,sugar substitutes, and prebiotics in a variety of food products. Fructose oligosaccharidesare not hydrolyzed by enzymes of the digestivetract but can be fermented by bacteria in the large intestine.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Polysaccharides Digestible polysaccharides Starch and are digestible polysaccharides of glucose.Plant cellscontain both linear and branched forms of starch. Glycogen has a highly branched structure and is found in animal tissues, particularly muscle and liver. Starch Starch is one of the most abundant polysaccharides in plants, where it is stored in the seeds, tubers, roots, and some fruits. It is made of two polymers, a mostly linear [ α (1,4)- d - ] and the branched [ α (1,4)- d -glucan with branches linked to C6]. from different sources vary in structure, but typically amylopectin has an average chain length between branch points of 20to 25 glucose units. Typical starches contain 20% to 30% amylose and 70% to 80% amylopectin; however, high amylopectin (e.g., waxy corn, 98% amylopectin) and high amylose (e.g., high amylose corn, 55% to 85% amylose) starches are also available. Starches for food processing are producedfrom many sources. The most important sources are corn (regular, waxy, and high amylose), potato, rice, tapioca, and wheat. Therefore certain raw starch granules with high amylose content, particularly those in raw potatoes and green bananas, resist digestion.Thus, in contrast to the raw starches, cookedpotato and green banana starch are readily digested. Gelatinized starch is hydrolyzed to glucose in the gastrointestinal tract by the combined action of salivary and pancreatic α -amylases and the intestinal mucosal α – glucosidases (glucoamylase, sucrose/isomaltase). The α -amylases, which cleave the α (1,4)- linkages only, catalyze hydrolysis of starch to maltose, , maltotetrose, and oligosaccharides

Glycogen Animals store glucose for energy metabolism in the highly branched polymer glycogen which is similar to amylopectin except that it has numerous alpha 1 -6 branches and higher molecular weight. Glycogen contains a single reducing end and many non reducing ends. Even though glycogen is present in the liver and muscle cells it is more abundant in hepatic cells.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Other minor storage forms are present. found in yeasts and bacteria. Bacteria growing on teeth produces extracellular dextran that accumulates and becomes important constituent of dental plaque. Celluose and is a linear β (1,4)- d -glucan arranged as ribbon like chains are aligned in parallel arrays called microfibrils, wherein the chains are strongly hydrogen bonded to each other. The microfibrils are similarly packed together into strong fibers, which are very insoluble and stiffen the plant cell wall. Associated with cellulose in the cell wall are several other insoluble polysaccharides, the hemicelluloses. These include the xyloglucans, which have a cellulose-like backbone with α - d -xylose units linked to C6 of the glucosyl unit, and arabinoxylans, in which the β (1,4)- d -xylan chain has α - l -arabinofuranose and d - glucuronic acid branches at C2 or C3. Pectic Polysaccharides Pectic polysaccharides and other associated polysaccharides ( and arabinans) are present in the cell walls of immature plant tissues and in the interstitial spaces. Native pectic galacturonan in the plant tissue is relatively insoluble, but isolated commercial is soluble in hot water. Calcium ions form complexes with the galacturonic acid units of pectin, cross- linking the chains into a gel network. The calcium – pectin complex is also the basis for dietary low sugar, low-calorie fruit jams and jellies, whereas jellies prepared without calcium require a high sugar content to form a gel structure. 10.6 Natural and modified polysaccharides Glycoconjugates Conjugates of sugars and oligosaccharides play essential physiological roles. These glycoconjugates include the glycosaminoglycans and proteoglycans, the glycoproteins, and the glycolipids. Glycosaminoglycans Mucopolysaccharides are heteroglycans made of repeating units of sugar derivatives that includes amino sugars and ironic acids which are called glycosaminoglycans.They are important components of tissue structure. The extracellular spaces collagen and elastin fibers embedded in

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi a matrix of ground substance composed of GAG. The essential classes include hyaluronic acid,chondroitin sulphate, heparin,heparin sulphate,dermatan sulphate and keratin sulphate Hyaluronic acid Occurence : synovial fluid, ECM of loose connective tissue Hyaluronic acid is unique among the GAGs because it does not contain any sulfate and is not found covalently attached to proteins. It forms non-covalently linked complexes with proteoglycans in the ECM. Hyaluronic acid polymers are very large (100 - 10,000 kD) and can displace a large volume of water.

Dermatan sulfate (L-iduronate + GlcNAc sulfate)Occurence : skin, blood vessels, heart valves

Chondroitin sulfate (D-glucuronate + GalNAc sulfate)Occurence : cartilage, bone, heart valves ; It is the most abundant GAG.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Heparin and heparan sulfate (D-glucuronate sulfate + N-sulfo-D-glucosamine)Heparans have less sulfate groups than heparins Occurence : Heparin :component of intracellular granules of mast cells lining the arteries of the lungs, liver and skin Heparan sulfate : basement membranes, component of cell surfaces

Keratan sulfate ( Gal + GlcNAc sulfate) Occurence : cornea, bone, cartilage ; Keratan sulfates are often aggregated with chondroitin sulfates.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Proteoglycan Proteoglycans are large, complex macromolecules that consist of a protein core to which glycosaminoglycans are covalently linked. Proteoglycans are found in the plasma membrane and extracellular matrices of most eukaryotic cells, where they have many functions. They may play a role in cell – cell and cell – matrix interactions and bind to a variety of ligands. A proteoglycan may carry more than one covalently linked as well as additional oligosaccharides that are N - and O -linked to the core protein.

GLYCOPROTEINS Many proteins carry covalently linked oligosaccharides as minor components. The size and number of the oligosaccharide chains vary. The carbohydrate moieties of glycoproteins may help stabilize proteins, therefore inhibiting denaturation, and may be involved in protein folding in addition to other specific biological roles glycolipids.Cerebrosides and gangliosides, which are derivatives of sphingolipids are common glycolipids of mammalian systems. Large amounts of galactocerebroside and galactocerebroside 3-sulfate are found in the brain. Gangliosides are formed by the addition of sialic acid (N -acetylneuraminic acid) to diglycosylceramide;

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Gangliosides are found on the surface membranes of most cells, and they make up about 6% byweight of total brain lipids. Gangliosides are most highly concentrated in the ganglion cells of the central nervous system. Plants and microorganisms synthesize several simple glycolipids, which include fatty acid esters of the sugars and glycosides of diglycerides, hydroxy fatty acids, and myo- inositol – containing phospholipids.

Glycolipids Glycolipids and Lipopolysaccahrides are membrane components Glycoproteins and proteoglycans are not the only cellular components that bear a complex oligosaccharide chains/; some lipids ,too, contains covalently bound oligosaccaharide chains. Glycolipids are widespread in nature but only as minor components of the lipid fraction and usually in association with proteins. In Ganglioside the polar head group is a complex oligosaccharide containing sialic acid and other monosaccharide units. The cerebrosides and gangliosides, which are glycosyl (glucosyl or galactosyl) derivatives of sphingolipids are common glycolipids of mammalian systems. These glycosphingolipids contain a base such as sphingosine, which has an 18-carbon monounsaturated chainsubstituted with two hydroxyl groups and anamine group .The amine nitrogen of the sphingosine unit is acylated with a long- chain (14- to 26-carbon) fatty acid. Cerebrosides are neutral glycosphingolipids, whereas sulfatides are acidic glycosphingolipids.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Gangliosides are found on the surface membranes of most cells, and they make up about 6% by weight of total brain lipids. They are most highly concentrated in the ganglion cells of the central nervous system. Abnormal glycosylation expressed in glycosphingolipids in tumor cells is strongly implicated as an essential mechanism in tumor progression. Unusual accumulation of specific glycosphingolipids in specific cancers has been correlatedwith altered cell – cell or cell – substratum interactions, and reagents that block glycosylation have been shown to inhibit tumor cell metastasis.

Code and Title of the Paper: F10NB Nutritional Biochemistry Code and Title of the Module: F10NB02 Different Classes of Carbohydrates and their Structures Name of the Content Writer: Dr. S. Sumathi

Lipopolysaccahrides are the major components of the outer membrane of gram negative bacteria such as E.coli and Salmonella typhimurium

The lipopolysaccaharide of S.typhimurium contains six fatty acids bound to 2 glucosamine residues,one of which is the point of attachment for a complex oligosaccharide. Lipopolysaccaharides are dominant on the surface of gram-negative bacteria; they are prime targets of the antibodies produced by the immune system produced in reponse to bacterial infection. Some bacteria’s lipopolysaccahride is toxic to humans and other animals; for example, it is responsible for the dangerously lowered blood pressure that occurs with toxic shock syndrome in Staphylococcus aureus infections in humans. CONCLUSION This module has giving us an overview of the structure and functions of various classes of carbohydrates. The significance and their structural and functional role of both simple and complex carbohydrates have been dealt with in this module.