carbohydrate chenmistry-1 MBcHB 1.2.pptx

Carbohydrates

1. Chemistry of Carbohydrates

2. Chemistry of Carbohydrates Definition of carbohydrates: First Definition (Old definition) : Carbohydrates are substances containing carbon, hydrogen and oxygen having the general formula CnH2nOn . Hydrogen and oxygen are present in 1:2 ratio the same ratio as water, so the French called them “Hydrates de Carbon”, i.e., carbo-hydrates Cn(H2O)n. Second Definition (new definition): Carbohydrates are aldehyde (CHO) or ketone (C=O) derivatives of polyhydric alcohols (have more than one OH group) or compounds which yield these derivatives on hydrolysis.

3. Biological Importance of Carbohydrates: Energy Source: Carbohydrates are primary sources of energy in organisms, with glucose being a key energy molecule. Cellular Recognition: Carbohydrates on cell surfaces play a vital role in cell-cell recognition and signaling. Structural Support: Polysaccharides like cellulose and chitin provide structural support to plant cell walls and arthropod exoskeletons, respectively. Glycoproteins and Glycolipids: Carbohydrates are often linked to proteins and lipids, forming glycoproteins and glycolipids that are crucial for cell membrane stability and signaling. Blood Group Determination: Blood groups are determined by specific carbohydrate antigens present on the surface of red blood cells.

4. Classification of carbohydrates According to the number of sugar units in the molecule there are three type: Monosaccharides (simple sugars ): They contain one sugar unit, i.e., and the simplest form of sugars and cannot be further hydrolyzed. They represent the end products of carbohydrate digestion in the human body. Oligosaccharides: They contain 2 – 10 monosaccharide units per molecule and give monosaccharides on acid hydrolysis. Polysaccharides: They contain more than 10 monosaccharide units per molecule and give monosaccharides on acid hydrolysis.

5. Monosaccharides They are classified according to the number of carbon atoms into five important groups. Each of these groups is subdivided according to the type of functional chemical group into: Aldoses (sugars containing aldehyde group) and Ketoses (sugars containing ketone group). Stereochemistry Position of the OH group on the chiral carbon furthest from the carbonyl carbon determines the D and L configuration of the monosaccharide. D is to the right and L is to the left of the Fischer projection as related to glyceraldehyde The L is a mirror image of D, thus termed as enantiomers

6. Important monosaccharides Glucose – important energy source for brain cells and RBC Fructose – got from fruits and honey. It is used in large amounts in the male reproductive tracts. Galactose – necessary for synthesis of biomolecules like lactose, glycolipids, glycoproteins and proteoglycans Ribose and deoxyribose

7. Stereochemistry/Configuration Stereochemistry is a critical aspect of carbohydrate chemistry because the spatial arrangement of atoms in these molecules greatly influences their biological properties and reactivity. Carbohydrates, especially monosaccharides, contain multiple chiral centers. They can exist in different stereoisomeric forms that have distinct properties, including taste, interaction with enzymes, and biological activity. Monosaccharides exhibit optical isomerism, all except dihydroxyacetone have a chiral carbon A chiral carbon has 4 different groups attached to a carbon making it asymmetric. Vant Hoff’s rule Possible number of isomers = 2 n Possible number of enantiomers = 2 n-1 (Where n is the number of chiral carbons)

8. Chirality and Chiral Centers in Carbohydrates Chirality arises when a carbon atom is attached to four different groups, making it asymmetric. Such carbon atoms are called chiral centers or stereocenters . The number of stereoisomers a molecule can have is determined by the number of chiral centers using the formula 2n2^n2n, where n is the number of chiral centers. For example Glucose (C₆H₁₂O₆): Glucose has four chiral centers (C2, C3, C4, and C5), giving rise to 24=162^4 = 1624=16 possible stereoisomers. However, in nature, only specific isomers, such as D-glucose, are biologically relevant.

9. D- and L- Configuration (Fischer Projections) Carbohydrates can be classified into D- and L-forms based on the orientation of the hydroxyl group (-OH) on the chiral carbon farthest from the carbonyl group (C=O), usually represented in a Fischer projection . In Fischer projections D-sugars: The hydroxyl group on the chiral center farthest from the carbonyl carbon is on the right. D-sugars: The hydroxyl group on the chiral center farthest from the carbonyl carbon is on the right. Example: D-Glucose vs. L-Glucose: In D-glucose, the hydroxyl group on carbon 5 is on the right, while in L-glucose, it is on the left. Most naturally occurring sugars are in the D-configuration .

10. Stereochemistry

11. Based on hydroxyl group on last carbon (aldose and ketose)

12. Properties of monosaccharides

13. Optical activity Definition: It is the ability of the sugar to rotate the plane of plane polarized light. The sugar that rotates the light to the right is called dextrorotatory (d or +) such as glucose, galactose and starch and that rotating light to the left is called levorotatory (l or -) such as fructose and invert sugar .

14. Cyclization of glucose to its hemiacetal form 5C and 6C sugars can cyclize through intramolecular nucleophilic attack of one of the OHs of the carbonyl C of the aldehyde or ketone. This forms stable 5 ( furanose ) or 6 ( pyranose ) member rings. The carbonyl O becomes an OH which points either below the ring ( α anomer ) or above the ring ( β anomer )

15. Cyclization of fructose

16. Anomers : 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 carbon in anomers are known as anomeric carbon or anomeric center. They are stereoisomers which differ in distribution of H and OH group around the asymmetric anomeric carbon atom C1 in aldoses or C2 in ketoses after cyclization of the molecule, e.g.

17. Epimerization They are stereoisomers which differ in distribution of H and OH groups around a single asymmetric carbon atom other than the anomeric and DL-form creating carbon before the last i.e., without difference on other carbon atoms. Ribose is an epimer to each of arabinose and xylose. Glucose is an epimer to each of mannose and galactose .

18. Formation of Hemiacetals/Hemiketals They are formed when an alcohol oxygen atom adds to the carbonyl carbon of an aldehyde or a ketone. Via the nucleophilic attack of the hydroxyl group at the electrophilic carbonyl group. Since alcohols are weak nucleophiles, the attack on the carbonyl carbon is usually promoted by protonation of the carbonyl oxygen. When this reaction takes place with an aldehyde, the product is called a ‘hemiacetal’; and when this reaction takes place with a ketone, the product is referred to as a ‘hemiketal’.

19. Reactions of monosaccharides

20. 1. Mutarotation This is the change in specific rotation of a chiral compound due to epimerization. When a monosaccharide such as glucose is dissolved in water, it exists in equilibrium between its open-chain form and its cyclic α- and β-forms. As the cyclic forms open and reclose, the hydroxyl group on the anomeric carbon can switch between the α- and β-configurations. Example: D-glucose in solution will mutarotate between α-D-glucose and β-D-glucose, leading to an equilibrium mixture with a specific optical rotation.

21. Reducing Property Reducing Sugars: Monosaccharides are classified as reducing sugars because they contain free aldehyde or ketone groups in their open-chain forms. This allows them to reduce oxidizing agents, copper(II) sulfate (CuSO₄) to form copper(I) oxide (Cu₂O), which precipitates as a red solid in Benedict's test. Reduction of Carbonyl Group: The aldehyde (in aldoses) or ketone (in ketoses) is reduced to a secondary or primary alcohol. C6​H12​O6​+H2​→C6​H14​O6 Aldoses vs. Ketoses: Aldoses (e.g., glucose) have an aldehyde group that can directly act as a reducing agent. Formation of Sugar Alcohols: Monosaccharides can be reduced to form sugar alcohols (alditols) by converting the carbonyl group (aldehyde or ketone) into a hydroxyl group. Glucose → Sorbitol: Glucose can be reduced to sorbitol, a sugar alcohol widely used as a sweetener in sugar-free products and as a laxative. Fructose → Mannitol: Fructose can be reduced to mannitol, which is used medically as a diuretic and to reduce intracranial pressure Importance in Industry: Sugar alcohols are used as sweeteners and humectants in food products. However, excessive sorbitol accumulation in cells, particularly in diabetes, can lead to complications like cataracts and neuropathy.

22. Benedict’s and Fehling’s Test (Reduction of Copper) Monosaccharides, especially reducing sugars (those with a free aldehyde or ketone group), can reduce metal ions in alkaline solutions. Benedict's and Fehling's tests exploit this property to detect the presence of reducing sugars. Benedict's Test: A positive test (red precipitate) indicates the presence of a reducing sugar. The aldehyde group of aldoses reduces Cu²⁺ to Cu⁺, resulting in the formation of copper(I) oxide (Cu₂O). Example: D-glucose, a reducing sugar, gives a positive Benedict’s test, while sucrose, a non-reducing sugar, does not unless hydrolyzed.

23. Oxidation The open chain forms can undergo oxidation reduction reactions in the presence of oxidizing or reducing agents such as Fehling’s reagent (Cu II tartarate) and Tollen’s reagent (Ammonical silver nitrate solution). Oxidation of Aldehyde Group: The aldehyde group of aldoses can be oxidized to carboxylic acids, forming aldonic acids. For example, the oxidation of glucose yields gluconic acid using mild oxidizing agents like bromine water. Uronic Acid Formation: The oxidation of the terminal hydroxyl group (–CH₂OH) of monosaccharides leads to the formation of uronic acids, such as glucuronic acid from glucose. Glucuronic acid is crucial in the detoxification process in the liver, where it conjugates with toxins and drugs to make them more water-soluble for excretion in urine. The aldehyde group (–CHO) is oxidized to a carboxyl group (–COOH). C6​H12​O6​+[O]→C6​H10​O7​+H2​O

24. 4. Esterification The hydroxyl groups of carbohydrates react as alcohols with acids and acid anhydrides to give esters. Esterification often dramatically changes a sugar’s chemical and physical properties Sulfate esters of carbohydrate molecules are found predominantly in the proteoglycan components of connective tissue Participate in forming of salt bridges between carbohydrate chains Phosphate Ester Formation: Monosaccharides can form ester bonds with phosphoric acid, leading to the formation of sugar phosphates. Nucleotide Sugars: Monosaccharides can also form nucleotide sugars, where a sugar is linked to a nucleotide (e.g., UDP-glucose), which serves as a donor in glycosylation reactions.These sugar phosphates are important intermediates in cellular metabolism, such as glucose-6-phosphate in glycolysis.

25. Glycosidic Bonds formation Glycosidic bonds formed between monosaccharide units are the basis for the formation of oligosaccharides and polysaccharides. Acetal Formation: Monosaccharides can react with alcohols to form glycosidic bonds, resulting in the formation of disaccharides, oligosaccharides, or polysaccharides. This reaction involves the hemiacetal or hemiketal group of the monosaccharide reacting with the hydroxyl group of another sugar molecule, forming an acetal or ketal linkage Importance in Biological Molecules: Glycosidic bonds are critical for the formation of complex carbohydrates like starch, glycogen, and cellulose 30

26. 5. Formation of glycosides

27. N- glycosidic bond. The anomeric carbon atom of a sugar can be linked to the nitrogen atom of an amine to form an N- glycosidic bond. 32

28. Formation of Sugar Phosphates Phosphorylation of monosaccharides is a key step in metabolic pathways like glycolysis. Reaction Mechanism: Phosphorylation: Addition of a phosphate group (–PO₄²⁻) to a hydroxyl group. Glucose to Glucose-6-Phosphate: Glucose+ATP→Glucose-6-Phosphate+ADP Catalyzed by hexokinase, this reaction traps glucose within the cell and prepares it for glycolysis. Fructose to Fructose-1,6-Bisphosphate Fructose-6-Phosphate+ATP→Fructose-1,6-Bisphosphate Catalyzed by phosphofructokinase-1, this is a key regulatory step in glycolysis.

29. Disaccharides Basically, there are three main disaccharides these includes; sucrose, maltose and lactose All are isomers with molecular formula C 12 H 22 O 11 . On hydrolysis they yield 2 monosaccharide. Soluble in water Even though they are soluble in water, they are too large to pass through the cell membrane. Formed by combination of 2 monosaccharides. Bonds between 2 monosaccharide are known as Glycosidic bond. Consider a combination of a molecule of alpha –glucose and a molecule of alpha glucose, the product is a beta maltose and water.

30. Formation of maltose

31. Glycosidic linkage between glucose.

32. Sucrose Is a sugar used at home (cane sugar) The bond is an α (1,2) glycosidic bond When hydrolyzed, it forms a mixture of α -glucose and β -fructose.

33. It is a dextrorotatory sugar but when it is hydrolyzed by sucrase enzyme or by acid hydrolysis (HCl) the mixture of sugars produced is levorotatory. This is because the levorotatory power of fructose (-92.5) cancels the dextrorotatory power of glucose (+52.5) since they are at equal proportions in the product. This is why this sugar is called invert sugar . Sucrase enzyme is therefore, also called invertase enzyme.

34. Maltose Commonly known as malt sugar. Present in germinating grain Bond α (1,4) glycosidic linkage Produced commercially by hydrolysis of starch.

35. Isomaltose Is a hydrolysis product of starch It has an α (1,6) glycosidic linkage of 2 glucose monomers.

36. Lactose Commercially known as milk sugar 0f animal origin Bond β (1,4) glycosidic linkage Bacteria cause fermentation of lactose forming lactic acid. When these reaction occur ,it changes the taste to a sour one. It is the most suitable sugar for baby feeding as a sweetener for milk because: It is the least sweet sugar so that the baby can nurse a large amount of mother’s milk without getting his appetite lost. Because it has a  - glycosidic linkage it is non-fermentable sugar, so it does not form gases and not cause colic to the infant. It has a laxative effect and prevents constipation and non-irritant to the stomach and does not induce vomiting. Unabsorbed sugar is used as a food for large intestinal bacteria that form a number of vitamins that benefits the baby.

37. Structure of lactose

38. Trehalose 2 glucose units linked through an α (1,1) glycosidic bond. It is abundant in fungi and found in hemolymph of insects.

39. Sugar derivatives Sugar acids Sugar alcohols Amino sugars Deoxy sugars

40. 3- Amino sugars : Replacing OH group on C2 by an amino group (NH2) produces them.

41. 4-Deoxysugars: These are sugars in which OH group is replaced by H. 1. At C2 gives Deoxy sugar proper deoxyribose that enters in structure of DNA.,

42. Proteoglycans They are composed of GAGs linked to proteins. The GAGs extent perpendicular from the core in a brush like structure The linkage between GAG and protein is a trisaccharide composed of 2 galactose residues and a xylulose residue.

43. Polysaccharides These are polymerized products of many monosaccharide units. They may be 1. Homoglycans are composed of single kind of monosaccharides, e.g. starch, glycogen and cellulose. 2. Heteroglycans are composed of two or more different monosaccharides, e.g. hyaluronic acid, chondroitin sulphate . Hexosans , A ny group of polysaccharides, including starch and glycogen, that form hexoses when hydrolyzed . I. Glucosans : Is glycogen a glucosan ? Glucosan is a general term for polysaccharides of glucose which produce only glucose on hydrolysis. Their examples includes; starch, dextrins , dextrans , glycogen and cellulose,

44. Starch: It is the stored form of carbohydrate of plants. It never exists in animals. It is present in cereals such as wheat and rice and tubers such as potatoes. It is in the form of starch granules. The core of the granule is amylose (20%) and the shell is amylopectin (80%). Due to its high molecular weight it forms colloidal solution in hot water.

45. Amylose Composed of long unbranched chains of D-glucose molecules linked by α (1,4) glycosidic bonds with only one reducing end. It has a compact shape that is ideal for storage due to its long linear tight helices During the iodine test, the iodine inserts itself into the helices, interacting electronically with the helically arranged glucose residues of amylose and stabilizes them to give and intense blue color.

46. Amylopectin: It forms the outer coat of starch granule and is insoluble in water. It is branched chains formed of a large number of  -glucose units linked by  -1,4-glucosidic linkage along the branch and by  -1,6-glucosidic linkage at the branching point that occur every 25-30 glucose units. Due to its high molecular weight, it forms a colloidal solution. Starch can be hydrolyzed by HCl or amylase.

47. Dextran : A compound formed of  -glucose units linked by  -1,4,  -1,3- and  -1,6-linkage present in the form of a network that is synthesized by certain bacteria having sucrose in its media. Products of hydrolysis of starch and include amylodextrin , erythrodextrin , achrodextrin which form color with iodine They have sweet taste. They are easily digested than starch as in corn and rice syrup. It has a great biochemical importance , It is used as plasma substitute to restore blood pressure in cases of shock. Iron used for treatment of iron deficiency anemia is used as dextran ferrous sulfate intramuscular injection. Sodium dextran sulfate is an anticoagulant.

48. Glycogen: It is the stored form of carbohydrate in animal, particularly in muscles and liver. Its structure is similar to amylopectin a branched tree with  -1,4-glucosidic linkage along the branch and  -1,6-glucosidic linkage at the branching point. The glycogen tree is shorter and more branched (a branch point every 8-10 glucose units) than amylopectin. It is digestible because human amylases hydrolyze  - glucosidic linkage. It forms granules in the cytoplasm and liver cells where enzymes associated with these granules hydrolyze the glycogen molecules and yield free glucose used in the production of energy.

49. Cellulose: It is a structural polysaccharide and forms the skeleton of plant cells and does not enter in animals cell structures. It is a straight chain molecule formed of a large number of  -glucose units linked by  -1,4-glucosidic linkage. It is water insoluble and enters in structure of cotton and paper It is the major food for herbivorous animal where it is fermented into volatile fatty acids. It is a linear structure with hydrogen bonding between adjacent glucose chains forming a fibrin. The hydrogen bonding facilitates in the formation of an insoluble compound. Its structural behavior is due to β (1,4) linkages that have a high tensile strength.

50. It is indigestible but is very essential in food for: Prevention of constipation by increasing the bulk of stools. Its fermentation by large intestinal bacteria give volatile fatty acids that is anticancer for colon cells and gives also some water soluble vitamins. It adsorbs toxins present in foods and prevents its absorption into the body.

51. Chitin It is a structural component of exoskeltons and in cell walls of many fungi. It is hardened by impregnation with calcium carbonate. It is linear and made by repeating residues of N-acetyl-D-glucosamine with β (1,4) glycosidic linkages.

52. Starch Glycogen Cellulose Nature: Stored form of carbohydrate in plants. Stored form of carbohydrates in animals. Structural form of carbohydrate in plant cells but prevents constipation in human. Source: Cereals, e.g., wheat, rice, and tubers, e.g., potatoes. Muscles and liver Linen and cotton are nearly pure cellulose. Solubility: Amylose is water soluble and amylopectin is insoluble. Water soluble forming colloidal solution. Water insoluble. Nature of the chains : Amylose is helical straight chain (  -glucose units linked by  -1,4-glucosidic bonds). Amylopectin is branched chain (  -glucose units linked by  -1,4- and  -1,6-glucosidic bonds). Branched chain similar to amylopectin but its trees are shorter and have more branches than amylopectin tree. Straight chain (large number of  -glucose units linked by  -1,4- glucosidic bonds). Reaction with iodine : Amylose gives blue color and amylopectin gives red color. Gives red color. No color. Digestibility: Is hydrolyzed by HCl or amylase into dextrins and maltose. Digestible by amylase into dextrins and maltose. Non-digestiblebut HCl hydrolysis gives cellobiose.

53. HETEROGLYCANS They are composed of two or more different monosaccharides, e.g. hyaluronic acid, chondroitin sulphate . These diverse sugar units are linked by glycosidic bonds, and their structures give rise to a variety of biological functions, depending on the specific heteroglycan . Hyaluronic Acid (HA) Composition : Hyaluronic acid is a heteroglycan composed of alternating units of D- glucuronic acid and N-acetyl-D-glucosamine. The disaccharide units are linked by β-1,3 and β-1,4 glycosidic bonds. Structural Component : It is a major component of the extracellular matrix in connective tissues, including skin, cartilage, and the synovial fluid of joints. Lubrication : HA acts as a lubricant in joints, reducing friction and wear on articular cartilage. Wound Healing : It promotes tissue repair and wound healing by supporting cell migration and proliferation. Hydration : HA can retain large amounts of water, contributing to tissue hydration and maintaining skin elasticity. Anti-inflammatory : HA plays a role in modulating the inflammatory response and is involved in the healing of damaged tissues

54. Chondroitin Sulfate Composition : Chondroitin sulfate is made up of repeating disaccharide units of glucuronic acid and N- acetylgalactosamine , which may be sulfated at various positions. Linkage: The disaccharide units are linked by β-1,3 and β-1,4 glycosidic bonds Functions Cartilage Function : It is a key component of cartilage, contributing to its structural integrity and resistance to compression. Joint Health : Chondroitin sulfate helps maintain joint flexibility and reduces the degradation of cartilage, making it an important supplement in the treatment of osteoarthritis. Anti-inflammatory : It has anti-inflammatory properties that help reduce joint inflammation and pain. Water Retention : Like hyaluronic acid, chondroitin sulfate attracts and retains water, enhancing the shock-absorbing properties of cartilage.

55. Heparin Composition : Heparin is a sulfated heteroglycan composed of glucosamine and iduronic acid or glucuronic acid Functions Anticoagulant : Heparin is widely used as a blood thinner to prevent blood clots during surgery or in patients at risk of thrombosis. Regulation of Blood Flow : By inhibiting clot formation, heparin ensures proper blood flow and reduces the risk of blockages in the blood vessels. Cell Signaling : Heparin also has roles in regulating cell growth and immune function Keratan Sulfate Composition : Keratan sulfate is composed of repeating units of galactose and N- acetylglucosamine . linked by α-1,4 and α-1,6 glycosidic bonds. Functions Corneal Transparency : It is important for maintaining the transparency of the cornea in the eye. Structural Support : Keratan sulfate is a component of cartilage and plays a role in the maintenance of its structure and function. Bone and Cartilage Repair : It is involved in the regeneration of bone and cartilage tissue.

56. Dermatan Sulfate Composition : Dermatan sulfate consists of L-iduronic acid and N-acetylgalactosamine, with varying degrees of sulfation. Functions Linkage: The disaccharide units are linked by β-1,4 and β-1,3 glycosidic bonds. Wound Healing : It is involved in the regulation of cell proliferation, wound healing, and tissue repair. Anticoagulant Properties : Dermatan sulfate also has anticoagulant effects, though less potent than heparin. Skin Health : It plays a role in maintaining the integrity and elasticity of the skin. Heteroglycans like hyaluronic acid, chondroitin sulfate, and others perform essential functions providing structural support in connective tissues to regulating processes like coagulation and inflammation. Their diversity in composition allows them to fulfill highly specialized biological roles in human health