Paper : 04 Module : 01 Metabolism of carbohydrates Prelude: Carbohydrates (Part-A) –Mono & Oligosaccharides Principal Investigator Dr.S.K.Khare,Professor IIT Delhi. Paper Coordinator Dr. Ramesh Kothari,Professor UGC-CAS Department of Biosciences Saurashtra University, Rajkot-5, Gujarat-INDIA Content Reviewer Dr. S. P. SinghProfessor UGC-CAS Department of Biosciences Saurashtra University, Rajkot-5, Gujarat-INDIA Dr. Ramesh Kothari,Professor Content Writer UGC-CAS Department of Biosciences Saurashtra University, Rajkot-5, Gujarat-INDIA 1 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Description of Module Subject Name Biochemistry Paper Name 04 Metabolism of Carbohydrates Module Name/Title 01 Prelude: Carbohydrates (Part-A)- Mono & Oligosaccharides Dr. Vijaya Khader Dr. MC Varadaraj 2 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides PRELUDE-CARBOHYDRATES(Monosaccharide’s and Oligosaccharides) Objectives 1. Introduction and the function of Functions of carbohydrates 2. To understand classification of carbohydrates 3. To study the characteristics of carbohydrates 4. To understand the properties of mono- and di- saccharides: 3 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Introduction Carbohydrates are one of the three major macronutrients in our diet representing a wide group of substances which include the sugars, starches, glycogen, gums and celluloses. Carbohydrates are known as the important energy source for living things. They comes from the process of photosynthesis, an endothermic reaction in which condensation of carbon dioxide takes place and which requires light energy and the pigment chlorophyll. The chemical component of carbohydrates is carbon, hydrogen, and oxygen. Generally, but not always the hydrogen and oxygen in carbohydrates are present in the proportion oftwo hydrogen atoms to one oxygen atom as in H2O, from which fact the term “carbohydrates” was derived The carbohydrates are actually or potentially hydroxy aldehydes or ketones, and in most cases they are polyhydroxy aldehyde or ketones compounds that can be hydrolyzed to them. It also means “hydrate of carbon” Plant biomass is made up of three fourths of carbohydrates but in animal body it is present in small quantities. In animal it is stored in the form of glycogen, sugar and their derivatives All living organism contains derived monosaccharides such as the sugar acids, amino sugars and the deoxysugars Derivatives of the carbohydrates also contain nitrogen, phosphates and sulfur compounds. Carbohydrates can combine with lipid and protein to form glycolipids and glycoproteins. Carbohydrates and their derivatives are present in all animal tissues and tissue fluids, blood and milk. The glucosides are a class of carbohydrates are derivatives which are frequent constituents of plants 4 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides The major components of living matter is formed from carbohydrates, proteins and fats This complex form of carbohydrates is required for the maintenance of cell structure and functions Presence of functional group like alcohol on almost every carbon makes the chemistry of carbohydrates a complex structure Carbohydrate may be exist in either a straight chain or a closed ring structure. The general reaction between the aldehyde and ketone part of the carbohydrates and alcohol groups forms the derivative called hemiacetals and hemiketals leads to the formation of ring structure. The most common basic structure of carbohydrates is closed rings Glucose is an example of a single closed ring carbohydrate Functions of carbohydrates The simplest carbohydrates are initially synthesized in plants by the process of photosynthesiswhich is a series of reactions. Carbohydrate functions as… bio Fuel primary Source of Energy storage food framework in body anticoagulant antigen hormone provide raw material for industry Essential for Fat Oxidation plays role in gastro-intestinal function add flavour to the diet play an important role in molecular recognition 5 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Classification The carbohydrates are sometimes referred to as the saccharides The word saccharides comes from the Greek word sakcharon meaning sugar Those carbohydrates such as glucose and fructose that cannot be hydrolyzed into simpler compounds are called simple sugars or monosaccharides Certain carbohydrates are made of two molecules of monosaccharides such as sucrose, lactose and maltose These carbohydrates are called dissarcharides. Similarly, trisaccharides are composed of three and tetrasaccharides of four monosaccharides molecules All these compound carbohydrates may be readily hydrolyzed into their constituent monosaccharides by heating with dilute acids or by the action of specific enzymes According to the number of C atoms and functional groups in its simplest form of carbohydrates are further classified The suffix –ose indicates the types of sugar. Nomenclature of carbohydrates based on number of carbon atoms 1. Triose= 3 carbon atom(Glyceraldehyde, Dihydroxyacetone 2. Tetrose= 4 carbon atom(Erythrose) 3. Pentose= 5 carbon atom(Ribose, Ribulose, Xylulose) 4. Hexose=6 carbon atom(Glucose, Galactose, Mannose, Fructose) 5. Heptose=7 carbon atom(Sedoheptulose) and so on 6 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Characteristics of carbohydrates Isomerism Isomers are defined as molecule with the same chemical formula and often with the same kinds of chemical bonds between atoms, but in which the atoms are arranged differently i.e. they have different structural formulae. Isomerism can be of two types: Structural isomerism and Stereoisomerism 7 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Monosaccharides Greek, mono=one; sakchron=sugar. Monosaccharides are the simplest sugar formed by the single molecules which furthercannot be hydrolyzed into smaller units. Depending upon the number of carbon arrangement in a unit, mono saccharides are subdivided into aldoses and ketoses. The aldoses and ketoses are represented by the following general formulas. 8 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Study of the chemical and physical properties of many sugar has shown the cyclic forms predominate over open chain structure, both in solution and in the solid state. Alcohol may react with aldehyde and ketone moieties of the carbohydrates to form an unstable compounds called hemiacetals or hemiketals, respectively. This is a reaction between two molecules, i.e., it is intermolecular In glucose the –OH on carbon 5 (C-5) can react intramolecularly with carbonyl group (on C-1) to form a stable, cyclic hemiacetal. The cyclic form of glucose is a sixmembered ring; such sugars are called pyranose because they resemble pyran. Fructose forms a five membered ring called furanose as it resembles furan. 9 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides The pyranose and furanose ring structure of sugar proposed by Haworth more accurately represent their actual configuration than do the older projection structures used by Fischer and other workers, though the older ring forms are still used extensively in writing reaction of sugars. The pyranose ring of a six carbon aldose sugar can exist in either a boat or a chair configuration The substituents attached to the ring carbon thatextend parallel to the symmetry are said to be axial (a) whereas those that extend outward from the axis are said to be equatorial (e). 10 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Stereoisomerism Many of the carbohydrates contain the same number of atoms and the same kinds of groups, yet definitely distinct substances For example, the formula C 6H12O6 represents 16 differently simple sugars all processing the structure CH2OH.CHOH.CHOH.CHOH.CHOH.CHO This is due to differently arrangement of the constituent groups of the molecules in space. This phenomenon represents what is called stereoisomerism (space isomerism) and these sugars are stereoisomers. An asymmetric carbon atom is a carbon when it is attached to four different types of atoms or groups When there are several asymmetric carbon atoms in a chain molecule and the end group are not identical, the number of stereoisomers possible is equal to 2 n, where n is the number of asymmetric carbon atoms For example glucose contains 4 asymmetric carbon and thus are 2 4= 16 isomers. The simplest monosaccharides is glyceraldehydes Glyceraldehyde has a single asymmetric carbon atom (the central one) and so two stereoisomers (also called optical isomers) are possible, that is two forms of glyceraldehyde, denoted as D- and L-glyceraldehyde, which are mirror images of each other It has been possible to relate the spatial configuration of sugars, amino acids and many other optically active substances of biological importance to the configuration of the dextro and levo forms of glyceraldehydes Monosaccharides can be named by a system that is based on the number of carbons with the suffix –ose added. There is also a system for numbering the carbons. They 11 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides are numbered sequentially, with the aldehyde or ketone group being on the carbon with the lowest possible number Optical isomerism When a beam of plane polarized lightthrough the solution of a non-racemic mixture, rotation of polarization occurs Carbohydrates contain asymmetric carbons, because of this carbohydrates are optically active, and rotating the plane polarized light The compounds which rotates the plane polarized light to the right (clockwise) is called dextrorotatory (indicated by d or +)and the compound which rotates the plane polarized light to the left (counter clockwise) is called levorotatory (indicated by l or -). 12 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Enantiomers An Enantiomers is one of two stereoisomers that are mirror images of each other and are non- superimposable Epimers Epimers are those sugars which differ with its isomers in configuration at only one asymmetric carbon D-glucose and D-galactose contains four asymmetric groups, and that all these groups are identical except the configuration at C-4 Such isomers are called are epimersTheprocess of interconversion of epimers is known as epimerization and epimerases catalyzes this reaction 13 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Properties of Mono saccharides: Mutarotation Glycoside Formation Reducing Power Reduction Oxidation with mild and strong oxidizing agent Methylation / Esterification Dehydration Osazoneformation with phenyl hydrazine. Glucose Glucose is an aldohexose – It is a poly hydroxyaldehyde and contains 6-carbon Carbohydrates are transformedinto simplest glucose which is the primary carbohydrates utilized by the body tissues. Glucose is the sugar of blood and other body fluids Disaccharide like sucrose, maltose and lactose and polysaccharides such as starch, cellulose and glycogen contains glucose as one of the monomers Glucose is 25% less sweet than sucrose Blood normally contains from 60 to 90 mg of glucose in each 100ml Galactose Galactose is an aldohexose It is a poly hydroxyaldehyde and a 6-carbon containing compound It is found in dairy products, sugar beets, pectin and gum Galactose is one of the monomer of the disaccharide lactose Galactose is 80% less sweet than sucrose It is epimers of glucose 14 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Fructose Fructose is a ketohexose It is a poly hydroxyketone and contains 6-carbon It is found in fruit, flowers, root vegetables and honey Disaccharide sucrose contains fructose as one monomer It is the sweetest of all naturally occurring carbohydrates and 175% sweeter than sucrose Fructose has higher solubility than other sugars Properties of oligosaccharides The oligosaccharides are composed of the disaccharides, trisaccharides and tetrasaccharides and are so designated to indicate the number of monosaccharides units involved in the structures Disaccharides is a sugar formed when a bond between the first carbon of one sugar and a hydroxyl group at any position on the other sugar is formed and a molecule of water is removed Sucrose, maltose, and lactose are the most important disaccharides. Each one of these on hydrolysis with either an acid or an enzyme gives two molecules of the monosaccharides by which it is made of. Sucrose It is called as table sugar Sucrose occurs especially in the juices of plants such as sugar beets, sugar cane sorgum, sugar maple and pine apple Ripe fruits are rich in sucrose 20% of sugar cane is sucrose It is non-reducing sugar, is relatively stable toward the action of alkali and in general does not give the reaction characteristic of the sugar groupand hence no reaction with the benedict’s reagent Hydrolysis of sucrose in an acidic solution or by enzyme invertase or sucraseresults in its monomer i.e. a molecule of fructoseandglucose Sucrose has an-1,2 glycosidic linkage 15 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Lactose Lactose is formed by the mammary glands and occurs to the extent of about 5 per cent in milk hence it is called as milk sugar Lactose is hydrolyzed by acids and the specific enzyme lactase into its constituent monosaccharides glucose and galactose It is reducing sugar forms osazones, a cyanhydrin and an oxime and is decomposed by alkali Lactose intolerance is a fairly common condition means deficiency of the lactase enzymewhich breaks glycosidic bond Lactose has an -1,4 glycosidic linkage A water molecule and lactose is formed with the dehydration of monomeric unit one -d-glucose and one -d-galactose Human milk differs fromcow’s milk in containing in addition to regular lactose, other oligosaccharides such as L-fucosyl-lactose, in which the deoxy sugar L-fucose is linked to galactose at carbon 2 16 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides Maltose Malt sugar Maltose is made of two glucose units and is formed when the enzyme amylase or diastase hydrolyzes starch. Maltose is formed as an intermediate product in the acid hydrolysis of starch and consequently is an important constituent of corn syrups, which are prepared by partial hydrolysis of starch with dilute acid Maltose is readily fermented by yeast Maltose has an -1,4 linkage Cellobiose Cellobiose is obtained as a product of the incomplete hydrolysis of cellulose It is composed to two molecules of glucose into which it is split by either acids or the enzyme emulsion It is reducing sugar and give the reaction characteristic of the sugar group Cellobiose bears the same relation to cellulose as maltose does to starch and glycogen 17 Biochemistry Metabolism of Carbohydrates Prelude: Carbohydrates (Part-A)-Mono & Oligosaccharides
