Biochemistry notes on Carbohydrates set 2 (2025).pptx

This is the summary of all Carbohydrates notes in Biochemistry

1. BIOCHEMISTRY NOTES SET 2

2. INTRODUCTION Carbohydrates are; Macromolecules also known as saccharides Hydrates of carbon with carbon(C), hydrogen(H) and oxygen(O) in the ratio of 1:2:1. Have a general formula C n (H 2 O) n where n is greater or equal to 3 NOTE: -Deoxyribose(C 5 H 10 O 4 ) doesn't follow the formula. It has an (-H) instead of (-OH) on the 2’ carbon which makes DNA more stable. As well as rhamnohexose (C 6 H 12 O 5 ), a deoxy sugar, meaning it has an (-H) instead of (-OH) on the 6 carbon.

3. - There are also non-carbohydrate compounds that satisfy the formula like lactic acid (C 3 H 6 O 3 ) Hence carbohydrates cannot be always considered as hydrates of carbon but rather polyhydroxy aldehydes or ketones. -Carbohydrates are the primary sources of energy for living organisms

4. Carbohydrates are the most abundant biomolecules on Earth and serve as the primary energy-yielding pathway in most non-photosynthetic cells. They are defined as polyhydroxy aldehydes or ketones , or substances that yield such compounds upon hydrolysis. The general empirical formula for carbohydrates is (CH₂O)ₙ , n = 3 and above representing a simplified structure. The elements are joined together by covalent bonds In carbohydrates, the ratio of hydrogen to oxygen is 2:1 as in water and so carbohydrates are called hydrates of carbon Carbohydrates can either be aldehydes when they contain a functional group ( -CHO ) or ketone with functional group ( C=O )

5. CLASSIFICATION OF CARBOHYDRATES There 3 major classes of carbohydrates; Monosaccharides Disaccharides Polysaccharides

6. 1. Monosaccharaides or simple sugars These are single sugar units like glucose, fructose and galactose a general formula C n (H 2 O) n They cannot be broken by hydrolysis to make up other sugars. They act as building blocks for other sugars . They are the simplest carbohydrates, consisting of a single polyhydroxy aldehyde or ketone unit. The most abundant monosaccharide in nature is D-glucose (dextrose), a six-carbon sugar. Other examples include fructose, galactose, and ribose.

7. 2. Disaccharides They are formed when two monosaccharide units combine by a condensation reaction . C 6 H 12 O 6 + C 6 H 12 O 6 C 12 H 22 O 11 + H 2 O Glucose + Glucose Maltose + Water Glucose + Fructose Sucrose Glucose + Galactose Lactose Bond formed when two monosaccharides join () is called a glycosidic bond . When the monosaccharides are glucose molecules, they will combine by condensation, the bond will be between position 1 and 4 of the carbon atoms giving a 1-4 glycosidic bond. N.B In cells, oligosaccharides consisting of 3 or more units do not occur as free entities but are joined to non-sugar molecules (lipids or proteins) in glycoconjugates.

8. Diagram showing condensation reaction to form disaccharide The monosaccharide units that have been linked to form dissaccharides and polysaccharides are called residues. The disaccharide formed show physical properties which involve the following. Small molecules Sweet Readily soluble in water Crystalline Their names end with suffix - ose The most common disaccharide are ; Maltose, lactose, sucrose.

9. 3.Oligosaccharides Comprising short chains of monosaccharide units (typically 3-10), linked by glycosidic bonds. Examples include; Raffinose ( composed of galactose, glucose, and fructose), stachyose

10. 4. Polysaccharides or complex sugars These are sugar polymers containing more than 10 monosaccharide units. Have high molecular weight and form colloids when dissolved in water. Some polysaccharides such as cellulose and starch are linear chains , others such as glycogen are branched. Long or short chains are formed, which can be either branched or unbranched, they can be folded and compact. They can be categorized based on their function. Do not diffuse easily out of the cells due to large sizes Easily hydrolyzed to their constituent monosaccharides which can be respired to provide energy. Other polysaccharides and polysaccharide derivatives(chitin, murein , inulin, pectin, hemicellulose, muco -polysaccharides)

11. Storage Polysaccharides : Such as starch, which serves as an energy reserve in plants, and glycogen, which serves as an energy reserve in animals. Structural Polysaccharides : Such as cellulose, which provides structural support in plant cell walls, and chitin, which provides structural support in insect exoskeletons. Polysaccharides show the following physical properties : Macromolecules(large molecules) Not sweet Insoluble or slightly soluble in water Not crystalline. Polysaccharides are multi-sugar with a general formula (C 6 H 10 O 5 )n . They are the ideal storage compounds in plants and animals. The properties which make them ideal storage compounds include the following: Are compact and folded so that large amount can take up small spaces within the cell Large size molecules make them insoluble in water, so they can exert no osmotic or chemical influence in cells.

12. NAMING OF CARBOHYDRATES Monosaccharides are primarily named based on their functional groups, the number of carbon atoms and stereochemistry.(Spatial arrangement of atoms in a molecule) The names end with an ( ose ) which means sugars and the following are considered; 1. Functional group 2. Number of carbon atoms 3. Stereochemistry 4. Cyclic structures 5.Polysaccharides

13. 1. Functional group Carbohydrates with the aldehyde (-CHO) group are called aldoses and those with the ketone (-CO) group become ketoses

14. 2. Number of carbon atoms Carbohydrate names are prefixed with tri for 3 carbon atoms, tetra for 4, penta for 5 hexa for 6 etc . Triose; three carbon atoms with formula (C 3 H 6 O 3 ) Tetrose : four carbon atoms e.g. erythrose , Erythrulose . They have general formula, C 4 H 8 O 4 Pentose: five carbon atoms (C 5 h 10 O 5 ),e.g. ribose , deoxyribose which has formula , C 5 H 10 O 4

15. Hexose: six carbon atoms with the formula,C 6 H 12 O 6 Eg glucose, fructose, galactose. With the two factors above we are able to name general groups of simplest carbohydrates following the order below, a) Prefix for the functional group e.g. Aldo- ,Keto b)base name according to number of carbon atoms. For example: Aldotrioses , ketotrioses etc.

16. 3. Stereochemistry Carbohydrates can exist in the D- and L-forms, based on the placement of the hydroxyl (-OH) group on the last chiral carbon. The D-form : If the hydroxyl group on the last chiral carbon is on the right while the L-form occurs when the hydroxyl group is on the left. For example: D-glucose, L-glucose

17. 4. Cyclic structures These carbohydrates form ringed structures . They are named as: a)pyranose- Six membered ring e.g. glucopyranose b) furanose - five membered ring e.g. fructofuranose

18. 5.Polysaccharides Are named according to their repeating sugar units:eg starch from glucose units, cellulose polymer of –D-Glucose, glycogen highly branched glucose polymer .

19. ISOMERISM OF MONOSACCHARIDES Isomerism is the phenomenon where compounds have the same molecular formula but different structures or spatial arrangements leading to variation in their properties They are divided into structural and stereo isomerism

20. Structural isomerism This is when two or more monosaccharides have the same molecular formula but different structural arrangement of atoms along the carbon chain Some of the examples of structural isomers of monosaccharides may include; Trioses(3C); This is seen in glyceraldehyde and dihydroxyacetone both with a chemical formula C 3 H 6 O 3. Pentoses (5C)

21. Stereo isomerism This refers to when two or monosaccharides have the molecular formula but different spatial arrangement of the atoms along the carbon chain.

22. NB: The broader study of the spatial arrangement of atoms in molecules and how this affects their chemical and physical properties is called stereo-chemistry. It plays a crucial role in determining their structure , function and biological interactions. The stereo isomers are mirror images of each other. Stereo isomerism occurs at the asymmetrical carbon atom/chiral center. A chiral center is a carbon atom bonded to 4 different atoms or group of atoms . Stereoisomerism is sub divided into;

23. 1. Enantiomers These are stereoisomers that are mirror images of each other that are not super imposable. They have opposite configurations at all chiral canters furthest from the carbonyl group. If the hydroxyl group is on the right hand side of the chiral carbon in the Fischer projection(Linear structures) , it’s a D-sugar and when the hydroxyl group is on the left hand side of the chiral center , its an L-sugar. Note; the most naturally occurring sugars are in the D form. Structural examples of enantiomers

24. 2. Epimers These are stereoisomers that differ in configuration at only one chiral center. Some epimers of glucose may include ; D-glucose, D-galactose differ at the 4’ carbon , D-mannose and D- glucose differ at the 2’ carbon.

25. 3. Anomers These are stereoisomers of monosaccharides that are in cyclic structures i.e. furanoses and pyranoses. The two anomers formed are called the  and  anomer. The -anomer arises when the -OH group on the 1’ carbon is below while the  anomer arises when the -OH group on the 1’ carbon is above.

26. Fischer projection of monosaccharides This is a two dimensional way of representing three dimensional molecules especially carbohydrates. Key features to note; 1. Vertical lines represent dash bonds( bonds going behind the plane or away from the viewer) 2. Horizontal lines represent wedge bonds( those coming out of the plane or towards the viewer) 3. Aldehyde group at C1 ,Ketone at C2 4. Each vertex is a stereo genic carbon (chiral center)

27. Harwoth projection of monosaccharides This is the cyclic representation of the ringed structured monosaccharaides called pyranoses and furanoses. Converting the Fischer projection into Harwoth projection procedure Rotate the Fischer projection through 90 in the clockwise direction. The atoms or groups on the right hand side will appear down in the cyclic form The atoms or groups on C5 and C6 will undergo an anticlockwise shift so as to bring the OH group in the right position to enable intramolecular bonding to form a six membered ring.

28. IMPORTANT MONOSACCHARIDES

29. GLUCOSE (C 6 H 12 O 6 ) Glucose is the most abundant carbohydrate. It is an aldohexose that serves as a primary source of energy for cells in the human body. The body produces glucose through breakdown of complex carbohydrates and proteins when needed. The breakdown of carbohydrates(glycogen ) through glycogenolysis and proteins through gluconeogenesis, stored in the liver and muscles produces glucose to maintain energy levels when needed. Glucose is a short term and long term energy reserve.

30. GALACTOSE Galactose is too an aldohexose . It is an epimer of glucose meaning it differs in configuration at just one carbon atom(carbon 4 in the structure). Galactose is part of lactose, a disaccharide found in milk. It is usually converted to glucose for cellular metabolism.

31. FRUCTOSE Fructose is a ketohexose found in fruits, honey and some vegetables. It has the same chemical formula as glucose but differs in that fructose is a ketone. Fructose is significantly sweeter than glucose. Unlike glucose which is directly absorbed in the blood stream during digestion, fructose is primarily metabolized primarily in the liver converting it to glucose, glycogen or fat.

32. RIBOSE ( C 5 H 10 O 5 ) Ribose is a 5 carbon sugar (pentose) that plays a crucial role in energy production, genetic material and cellular metabolism. Ribose is a structural component of RNA(ribonucleic acid) RNA more reactive and less stable which is why RNA is typically used for short term purposes such as energy production through synthesis of ATP(Adenosine Triphosphate) for cell respiration and metabolism.

33. DEOXYRIBOSE( C 5 H 10 O 4 ) Deoxyribose is also a 5 carbon sugar that plays a crucial role in the structure of DNA( deoxyribonucleic acid). Deoxyribose differs from ribose on the 2’carbon where it has an (-H) instead of (-OH) making DNA more chemically stable. The absence of the hydroxyl group makes it less reactive and less prone to hydrolysis than RNA. This stability is crucial since DNA stores genetic information for long term periods. It also helps in replication, mutations and transmission of genetic information from one generation to another.

34. CHEMICAL PROPERTIES OF MONOSACCHARIDES Hydrolysis : Carbohydrates break down into simpler sugars in the presence of water and enzymes or acids. Oxidatio n: They can be oxidized to form carboxylic acids, aldehydes, or ketones.( expect ketoses) Reduction : Carbohydrates can be reduced to produce alcohols or other reduced sugars. Glycosidic Bond Formation : They can form glycosidic bonds with other carbohydrates or non-carbohydrate molecules, leading to disaccharides, polysaccharides, or glycoconjugates . Acetylation : This process results in the formation of acetylated sugars. Methylation : Carbohydrates can be methylated, forming methylated sugars. Phosphorylation : This leads to the formation of phosphorylated sugars. Enzymatic Reactions : Carbohydrates participate in reactions like glycolysis, gluconeogenesis, and glycogen synthesis. Maillard Reaction : A non-enzymatic browning reaction between amino acids and reducing sugars. Caramelization : A non-enzymatic browning reaction occurring when sugars are heated to high temperatures.

35. PHYSICAL PROPERTIES OF MONOSACCHARIDES Solubility : Carbohydrates are generally soluble in water due to their hydroxyl groups, which form hydrogen bonds with water molecules. This property is crucial for their functionality in food and biological systems. Melting Point : The melting point of carbohydrates varies widely, influenced by their molecular structure and weight. For example, simple sugars have lower melting points compared to complex polysaccharides. Density : The density of carbohydrates is affected by their molecular structure. For instance, crystalline forms tend to have higher densities than amorphous forms due to more efficient packing. Viscosity : Polysaccharides significantly influence the viscosity of solutions. Their molecular weight and structure determine how they interact with water, affecting the flow properties of food products. Hygroscopicity : Many carbohydrates are hygroscopic, meaning they can absorb moisture from the environment. This property is important for food preservation and texture.

36. Thermal Properties : Carbohydrates exhibit specific thermal behaviors, including glass transition temperatures, which indicate the temperature range where they transition from a hard and glassy state to a softer, rubbery state. Crystallinity : Carbohydrates can exist in crystalline or amorphous forms, which affects their physical properties, such as solubility and melting point. Crystalline carbohydrates tend to be more stable and have distinct melting points. Optical Activity : Many carbohydrates are optically active, meaning they can rotate plane-polarized light due to their chiral structures. This property is significant in determining the purity and concentration of sugar solutions. Boiling Point : The boiling point of carbohydrates varies and is generally higher than that of water due to their molecular weight and hydrogen bonding capabilities. This property is important in cooking and food processing. Surface Tension : Carbohydrates can affect the surface tension of solutions, which is crucial in applications like emulsification and foaming in food products. Their ability to lower surface tension is utilized in various food formulations.

37. FUNCTIONS OF CARBOHYDRATES Primary source of energy Carbohydrates are the body’s primary source of energy .When consumed, they are broken down into simple monosaccharides, glucose which enters the blood stream and into cells. In cells respiration takes place to produce ATP (Adenosine triphosphate) the energy currency of the cell. This process is called glycolysis. Structural components Cell wall structure: Carbohydrates such as cellulose form the structural framework of plant cell walls for strength and rigidity .Also chitin found in the exoskeleton of insects and fungi cell walls.

38. Energy storage When there is excess glucose ,the body stores it in form of glycogen in the liver and muscles a process called glycogenesis. When energy is needed, the liver then releases glycogen back into the blood stream as glucose to provide ATP. If glycogen stores are full excess carbohydrates are converted into lipids(lipogenesis) and stored in the adipose tissues. Brain functions and nervous support The central nervous system relies on glucose as its main source of energy .Glucose is necessary for neurotransmitter production , memory formation and cognitive function. A lack of carbohydrates can cause fatigue , dizziness and difficult concentration.

39. Digestive health Fiber is a carbohydrate that the body cannot digest but it plays a crucial role in digestion. Soluble fiber (oats , apples, beans) help lower cholesterol and regulate blood sugar levels. Insoluble fibers (whole grains , vegetables)aid in stool movements preventing constipation and promoting gut health. Some carbohydrates aid in the synthesis of nucleic acids ,ribose is a constituent of RNA and deoxyribose is a component of DNA Carbohydrates can be converted into other molecules .When the level of proteins in the body lowers carbohydrates can be broken to amino acids which form proteins

40. INTRAMOLECULAR AND INTERMOLECULAR CYCLIZATION

41. CYCLIZATION Cyclisation This is the chemical process where a linear molecule forms a ring structure. In the context of carbohydrates, it is the transformation of linear sugar into a cyclic structure. Linear forms of sugar (open-chain) This is the simplest representation of sugar molecules where the carbon chain is fully extended and not cyclized. It relates with the Fischer projection which is a 2D drawing that shows the 3D arrangement of the atom. The carbonyl group is placed at or near the top of the chain Horizontal lines represent bonds coming out of the plane and the vertical lines represent bonds going into the plane.

42. Chirality and stereochemistry Carbohydrates are chiral molecules, meaning they have asymmetric carbon atoms (carbon atoms bonded to four different atoms). D and L configuration e.g. D-glucose and L-glucose. Anomeric carbon This is a carbon derived from the carbonyl group (aldehyde or ketone into the linear form of a sugar. During cyclisation the carbonyl carbon (C=O) becomes the anomeric carbon in the cyclic form and it is also bonded to two oxygen atoms, one in the ring and the other as a hydroxyl group or another substituent .

43. Anomers These are cyclic stereoisomers that differ in configuration of the hydroxyl group attached to the anomeric carbon. They are classified into two based on the orientation of the hydroxyl group on the anomeric carbon relative to the ring structure namely; Alpha ( α ) anomer The hydroxyl group on the anomeric carbon is on the opposite side of the ring relative to the group (trans configuration). In the Haworth projection, the OH group is down (below the plane of the ring) for D-sugar. Beta (β) anomer The hydroxyl group on the anomeric carbon is on the same side as the group (cis configuration). In the Haworth projection the OH group is up (above the plane of the ring) for D-sugar .  

44. Haworth projection This is away of representing the cyclic structure of carbohydrates in a simple two- dimensional form. It is useful for showing the ring structure of monosaccharides and the position of substituents like the hydroxyl group on the ring . The ring is drawn as a flat polygon (usually hexagon for pyranoses or pentagon for furanoses). The anomeric carbon ( ) is placed at the right most position of the ring. The substituents (OH and are shown as lines projecting above or below the plane of the ring. Hydrogen atoms are usually omitted for simplicity.  

45. The oxygen atom on the ring is placed at the top-right comer for pyranose and on the top corner for furanose . The anomeric carbon is placed at the right most position. Substituents on the left side of the Fischer projection are placed above the ring and those one the right are placed below the ring in the Haworth projection. For D- sugars, the OH group on the anomeric carbon is below the ring for α -anomers and above the ring for β - anomers.

46. INTRAMOLECULAR CYCLIZATION This involves the formation of ring structure within a single carbohydrate molecule. Monosaccharides with five or more carbon atoms in the backbone usually occur in solution as cyclic or ring structure in which the carbonyl group is not free as written in the open chain structure but has formed a covalent bond with one of the –OH group along the chain to form a hemiacetal or hemiketal ring.

47. In general, an aldehyde can react with an alcohol to form a hemiacetal or acetal . Cyclic formation in Glucose The C-1 aldehyde in the open chain form of glucose reacts with the hydroxyl group in the 5 th carbon atom to form an intramolecular hemiacetal. The resulting six membered ring is called pyranose because its similar to an organic molecule pyran .

48. The different forms of glucose are formed, when the –OH extend to the right, it is α -D-glucose or α -D- glucopyranose , when it extends to the left, it is called β -D- glucopyranose known as anomers .

49. Similarly a ketone can react with an alcohol to form a hemiketal or a ketal . The C-2 keto group in the open chain of fructose can react with the -OH group in the 5 th carbon atom to form an intramolecular hemiketal . This five membered ring is called furanose because it is similar to an organic compound furan .

50. Fructose also forms a fructopyranose ring where the second carbon reacts with the hydroxyl group of the sixth carbon atom. Both the fructopyranose and the fructofuranose are stable in fructose.

51. Factors influencing intramolecular cyclisation

52. INTERMOLECULAR CYCLIZATION This is a chemical reaction where two or more molecules combine to form a cyclic compound. In biochemistry, intermolecular cyclization plays a crucial role in the synthesis of various biomolecules such as amino acids, sugars and nucleotides. Qn; Distinguish between intermolecular cyclization and intramolecular cyclization : Intermolecular cyclization is a chemical reaction where two or more molecules combine to form a cyclic compound and the reaction occurs between different molecules, hence the term “inter” (meaning “between”) whereas intramolecular cyclization is a chemical reaction where a single molecule forms a cyclic compound through a reaction between two functional groups within the same molecule. In carbohydrates, an example of intermolecular cyclization is the formation of sucrose from glucose and fructose by the condensation reaction. The reaction is an intermolecular cyclization reaction because it involves the combination of two different molecules (glucose and fructose) to form a new compound (sucrose) which is cyclic.

53. Intermolecular Cyclisation is often seen in glycosylation reactions for example maltose formation from the glucose molecules and polymerization. There are different types of Intermolecular cyclisation of carbohydrates and these include Enzymatic cyclisation, Intermolecular Sugar Cyclisation (for example dextran formation, Levan formation), and Shift Base cyclisation. Schiff Base Cyclisation This is a type of intermolecular Cyclisation which involves a reaction between an amine (NH2) and an aldehyde or Ketone to form an imine (-C=NH). This type of Cyclisation is found in amino Sugar Synthesis for example cyclisation of amino sugars in the biosynthesis of glycoproteins. Enzymatic Cyclisation This type of cyclisation involves enzyme-mediated reactions that occur in glucose units undergoing cyclisation via α -1,4-glycosidic bonds forming cyclic oligosaccharides. An example of this is the formation of cyclodextrins (CDs).

54. Formation of Cyclodextrins (CDs) Cyclodextrins are cyclic oligosaccharides formed by enzymatic intermolecular cyclisation of glucose units Process of formation of Cyclodextrins A starch molecule is acted upon by an enzyme glycosyltransferase ( CGFase ) which catalyzes its breakdown into shorter glucose chains. It then reforms the glycosidic bonds by forming the α -1,4-glycosidic bonds among the molecules (D- glucopyranose ) leading to different sizes of cyclodextrins which include α - cyclodextrin (6 glucose units), β - cyclodextrin (7 glucose units), and the γ - cyclodextrin (8 glucose unit) . Significance of CDs ( Cyclodextrins ) Cyclodextrins are used in pharmaceuticals to enhance drug delivery by improving solubility, stability and bioavailability since they have the ability to form inclusion complexes with the hydrophobic drug molecules. Cyclodextrins are used in the food industry as encapsulating agents of flavors and aromas as they trap volatile compounds due to their inclusion formation ability to Prevent their loss and extend shelf life.

55. Intermolecular Sugar Cyclisation This is a type of Intermolecular cyclisation which occurs when a hydroxyl group from one sugar molecule attacks the anomeric carbon of another sugar molecule forming Cyclic oligosaccharide. Examples of Intermolecular Sugar Cyclisation Include Levan formation and Dextran formation, Levan Formation Levan formation Leaven is a homopolysaccharide made of D-fructose linked by β -2,6-glycosidic bonds formed by Intermolecular Cyclisation of fructose molecules. Process of formation Multiple Sucrose molecules which act as the primary sugar source are acted upon by an enzyme Levan sucrase which catalyzes its breakdown releasing fructose and glucose molecules, then the fructose molecule reacts intermolecularly by forming β -2,6-linkages with other fructose units and as the process proceeds a Levan polysaccharide is formed. Significance of Levan It is used in pharmaceuticals since its prebiotic promoting growth of bacterial gut, a bacteria which aids digestion.

56. Dextran Formation It is also a homopolysaccharide but made up of D-glucose units. Process of formation A Sucrose molecule is broken down under the influence of an enzyme Dextran sucrase which catalyzes its breakdown into glucose and fructose molecules, the glucose monomers undergo a polymerization reaction via α -1,6 glycosidic linkages forming linear dextran back born. Some of glucose molecules form side branches through α -1,3, α -1,4 linkages creating a branched polymer and with continued addition of the glucose molecules a dextran is formed. Significance of Dextran It is used in pharmaceuticals as plasma volume expander in conditions where rapid fluid replacement is needed such as surgery. It is used as food stabilizer due to its ability to retain moisture, improve texture enhancing shelf life of food products.

57. Factors that cause intermolecular cyclization Concentration of reactants : High concentrations of reactants can increase the likelihood of intermolecular cyclization due to the increased collision frequency between the reactants. Temperature : Elevated temperatures can increase the kinetic energy of reactants such that they move faster and collide more frequently with each other thus leading to an increased reaction rate and increased molecular motion. This therefore enables the fast moving molecules to overcome energy barriers and participate in chemical reactions including intermolecular cyclization. pH : The pH of the reaction environment can influence the likelihood of intermolecular cyclization by affecting the ionization state of reactants.

58. REDUCING SUGARS These are a type of sugar that can donate electrons to other molecules due to the presence of a free carbonyl group. This allows them to act as reducing agents in chemical reactions. Examples include: glucose, fructose, galactose(monosaccharides) Lactose, maltose( disaccharides) They exist in both linear(open chain) form and cyclic(ring). In linear form, the carbonyl group is exposed hence the aldose readily react with the reagents

59. But for the ketose, only react as reducing reagents through a process called tautomerization where a keto form interconverts with an enol( a carbon-carbon double bond adjacent to hydroxyl group) which can donate electrons. In the cyclic form, the aldose form a hemiacetal group and the ketose form a hemiketal group that have the ability to open up into their linear form when in solution phase therefore exposing the carbonyl group . Importance of reducing sugars They are the primary source of energy for cells. Reducing sugars are involved in glycolysis which is a metabolic pathway that converts glucose into energy. They are used in various industries such as food , brewing and pharmaceuticals.

60. NON-REDUCING SUGARS Are a class of carbohydrates that lack a free aldehyde or ketone group and due to this, they do not take part in reduction reactions such as Benedict’s test or Fehling’s test. These sugars are more stable than reducing sugars and less reactive in certain chemical processes. Examples include sucrose(C 12 H 22 O 11 ), trehalose (C 12 H 22 O 11 ), raffinose (C 18 H 32 O 16 ), stachyose (C 24 H 42 O 21 )

61. Properties of non-reducing sugars Lack of reducing ends : They lack a free aldehyde or ketone group which means they cannot participate in oxidation-reduction reactions. This particular property renders them non-reactive to tests like Benedict’s or Fehling’s. Stability : Due to their structure, non-reducing sugars are generally more stable than reducing sugars which makes them less likely to undergo certain chemical reactions making them ideal for storage and long-term use. Formation : They are formed when two monosaccharides join together through a glycosidic bond. Solubility : They are often highly soluble in water which why they are commonly used in beverages and other liquid products. Hydrolysis : When non-reducing sugars are hydrolyzed, they break down into their constituent monosaccharides.

62. Sucrose condensation

63. DIFFERENCES

64. GLYCOSIDIC BONDS A glycosidic bond is a type of covalent bond that connects a carbohydrate (sugar) molecule to another group which can also be a carbohydrate or a different molecule. This bond is formed between the anomeric carbon of a monosaccharide and a hydroxyl group of another sugar or alcohol. Types of glycosidic bonds a) O- glycosidic bonds These are the most common type where the bond is formed between the anomeric carbon of a sugar and hydroxyl group of another group. b) N- glycosidic bonds These involve the anomeric carbon of a sugar and nitrogen atom commonly found in nucleosides and nucleotides.

65. Formation of glycosidic bonds By a reaction mechanism Glycosidic bonds are formed through condensation reaction where a molecule of water is eliminated as two monosaccharides come together. The anomeric carbon of one sugar and hydroxyl group on another sugar ( or non-carbohydrate molecule) participate in this reaction forming an acetal or ketal derivative.

66. Naming of glycosidic bonds Based on anomeric configuration Alpha(α) glycosidic bond : The hydroxyl group on the anomeric carbon is oriented downward ( on the opposite side from the CH2OH group) for example ( α – 1,4 glycosidic bond formed between 2 glucose units ). Beta( β ) glycosidic bond : The hydroxyl group on the anomeric carbon is oriented upward for example lactose (β – 1,4 glycosidic bond between glucose and galactose ). Based on carbon atoms involved 1-4 glycosidic bond : This bond forms between the anomeric carbon of one sugar and the hydroxyl group on the C4 carbon of another sugar. 1-2 glycosidic bond : This bond forms between anomeric carbon of one sugar and hydroxyl group of the C2 carbon of another sugar for example sucrose ( glucose + fructose ).

67. Characteristics of glycosidic bonds Stability : Glycosidic bonds are generally stable but can be hydrolyzed under acidic or enzymatic conditions, basic. Directionality : The bond has directionality meaning it links specific carbons on the sugar molecules for example maltose, the glycosidic bond is between C1 of the glucose and C4 of another glucose molecule.

68. Biological significance of glycosidic bonds Energy storage : In polysaccharides, glycosidic bonds link glucose units such as starch and glycogen which serve as energy storage molecules in plants and animals respectively. Structural component : In cellulose, glycosidic bonds in β -1,4 glycosidic bonds provide structural integrity to plant cell walls making cellulose resistant to hydrolysis . Genetic information, DNA and RNA rely on glycosidic bonds to connect sugars to bases. Cell communication; Glycoproteins and glycolipids help in cell signaling and immune.

69. Hydrolysis of glycosidic bonds Glycosidic bonds can be hydrolyzed breaking them down into individual monosaccharides. This process occurs via: Acid hydrolysis : Heating sugars in the presence of acid can cleanse glycosidic bonds. Enzymatic hydrolysis : Enzymes such as amylase ( for starch) and cellulase ( for cellulose) facilitate the breakdown of polysaccharides into monosaccharides in biochemical pathways.

70. DISACCHARIDES Disaccharides consists of two sugar molecules. They have a general formula of C 12 H 22 O 11. Disaccharides are formed when two monosaccharides covalently join by an O- glycosidic bond . The hydroxyl group of one monosaccharide combines with the hydrogen atom of another monosaccharide releasing a water molecule through a condensation reaction . In a hydrolysis reaction, the glycosidic bonds in disaccharides are broken down to form their respective monosaccharides.

71. FORMATION OF DISACCHARIDES C 6 H 12 O 6 + C 6 H 12 O 6 C 12 H 22 O 11 + H 2

72. CHARACTERISTICS OF DISACCHARIDES They are soluble in water They are sweet They can crystallize They have a low molecular mass They are reducing sugars except sucrose

73. EXAMPLES OF DISACCHARIDES

74. MALTOSE It is also known as malt sugar. It is formed from two α -D glucose molecules held together by α (1 → 4) glycosidic bond. It is mostly found in germinating seeds like barley . Maltose can be hydrolyzed by a dilute acid or the enzyme maltase to form two molecules of α -D glucose. It is a reducing sugar.

75. Formation of maltose

76. SUCROSE It is also known as cane sugar . It is formed from α -D glucose and β -D fructose. It is the main form in which carbohydrates are transported in plants. It is mostly abundant in sugarcane and sugar beets. It is a non reducing sugar.

77. Formation of sucrose

78. LACTOSE It is also called milk sugar. It is formed from β –D glucose and β - D galactose held together by β (1→ 4) glycosidic bond Lactose milk is the most important in the nutrition of young mammals. Lactose is a reducing sugar.

79. Formation of lactose

80. IMPORTANCE OF DISACCHARIDES Sucrose is a product of photosynthesis which functions as a major source of carbon and energy in plants. Lactose is a major source of energy in mammals . Maltose is an important intermediate in starch and glycogen digestion. Trehalose is an essential energy source for insects. Cellobiose is essential in carbohydrate metabolism.

81. Summary of disaccharides and their respective monomers

82. POLYSACCHARIDES A polysaccharide is a long chain molecule (polymer) made up of a small units (monomers) called monosaccharides. Polysaccharides function chiefly as storage and structural materials. They are convenient storage materials for several reasons; their large size makes them more insoluble in water, so they exert more osmotic pressure or chemical influence in the cell. They fold into compact shapes that are easily converted to simple sugars by hydrolysis. They are characterized by high melting points, insolubility or slightly soluble in water, not crystalline and are not sweet. Polysaccharides are divided into homopolysaccharides and heteropolysaccharides . The homopolysaccharides are composed of repeating units of the same monosaccharide while heteropolysaccharides are composed of repeating units of two or more different monosaccharides.

83. Homopolysaccharides 1) Starch (Storage polysaccharide) It is a polymer of glucose and a major fuel/energy store in plants for example potatoes, cassava etc. Starch has two major components i.e. Amylase and amylopectin. Amylase has a straight chain of glucose monomers linked by α-1,4-Glycosidic bonds. Amylopectin has both a branched and a straight chain of glucose monomers. The straight chain has α-1,4-glycosidic bonds while α -1,6-glycosidic bonds for the branch.

84. 2) Glycogen (Storage polysaccharide ) It is made up of glucose monomers and an equivalent to starch in plants but found in animals mainly for energy storage. Glycogen is converted to glucose through a process called glycogenolysis , this process ensures that glucose is released into the bloodstream when energy is needed, while also maintaining proper blood glucose levels. Glycogen is highly branched just like amylopectin and has both α -1,4-glycosidic bonds and α -1,6-glycosidic bonds.

85. 3) Cellulose (structural polysaccharide) This is found in plant cells for structural support. It has long chains of glucose monomers linked together by β-1,4-glycosidic bonds.

86. Most animals cannot use cellulose as an energy source, because they lack the enzymes that hydrolyze the linkages. However, termites readily digest cellulose eg wood because their intestine harbors a symbiotic microorganism, called trichonympha , that secretes enzymes called cellulose, which hydrolyzes the linkages. Ruminants have microbes in their stomach that helps in the digestion of cellulose. Wood-rot fungi and bacteria also produce cellulose.  

87. 4) Chitin ( structural polysaccharide) This is closely related to cellulose in structure and function. It occurs in some fungi cell walls and in some animal groups like arthropods in the exoskeleton. Chitin is a polymer of acetyl glucosamine and forms bundles of long parallel chains just like cellulose. Structurally, it is identical to cellulose except that the hydroxyl (-OH) group at carbon atom two is replaced by –NHCOCH 3

88. DEXTRINS Is a lower molecular weight polysaccharides produced by the partial hydrolysis of starch or glycogen. It consist of glucose molecules linked mainly by linked glycosidic bonds. Are often referred to as either amylodextrins , erythrodextrins or achridextrines Used as mucilage (glues) in adhesive for stamps, envelops and cardboard. Used in infant formulas (prevent the curding of milk in baby’s stomach) Ingestible dextrin are developed as soluble fiber supplements for food products Also used as stabilizers, thickening agents and energy source (because they are easily digestible) in food processing. A drug carrier and tablet binder in pharmaceuticals, as a sizing agent to strengthen threads during weaving in textiles  

89. Structure of dextrins

90. DEXTRANS Are bacterial and yeast homopolysaccharides made up of linked poly D-glucose. All have branches and some also have or branches. Dental plaque, formed by bacteria growing on the surface of teeth, is rich in dextrans Synthetic dextrans are used in several commercial products eg sephadex that serve in the fractionation of proteins by size-exclusion (gel filtration) chromatography. This mean dextrans are used as molecular sieves to separate proteins and other large molecules. The dextrans in these products are chemically crossed linked to form insoluble material of various porosities, to separate the macromolecules depending on their molecular sizes .  

91. INULIN It’s a storage polysaccharides linked fructofuranoses Linear, no branching Lower molecular weight than starch Produce yellow color with iodine. When hydrolyzed, yields fructose Its used as diagnostic agent for the evaluation of glomerular filtration rate(renal function test) SOURCES OF INULIN: Onions, garlic, dandelions and Jerusalem artichokes  

92. Uses of inulin Used clinically as s high accurate measure of glomerular filtration rate. Used as a soluble dietary fiber Used as appetite suppressant Used as a low glycemic index sweetener Used as a fat/cream substitute

93. AGAR (GALACTOSAN) Agar is a galactose polymer Obtained from the cell wall of some species of red algae seaweeds ( sphaerococcus Euchema ) and species of Gelidium Dissolve in hot water and in cooled water it becomes gelatinous. Used as a culture medium for microbiological work, also used as a laxative and a vegetarian gelatin substitute. A thickener for soups, in jellies, ice cream and some desserts As a clarifying agents in brewing, and for sizing fabrics

94. PECTIN Are found as intercellular substances in the tissues of young plants and are especially abundant in ripe fruits such as guava, apples and pears Pectin is a polysaccharides of - 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. They are referred to as polygalacturonides .  

95. HETEROPOLYSACCHARIDES/MUCOPOLYSACCHARIDES Are complex carbohydrates composed of 2 or more different types of disaccharides units. They often have structural or protective functions in living organisms and are branched structured. Thus, mucopolysaccharides are composed not only of a mixture of simple sugars but also derivatives of sugars such as amino sugars and uronic (acid sugar) Found in both plants and animal Also known as glycoaminoglycans , carbohydrates containing a repeating disaccharides. Acid sugar is a D- glucuronic acid or its C-5 epimer iduronic acid Amino sugar is either D-glucosamine or D- galactosammine , and the amino group is usually acetylated eliminating its positive charge.

96. 1. S tructural Heteropolysaccharides Peptidoglyca n: found in bacterial cell walls, composed of sugars and amino acids Hyaluronic acid : present in connective tissues, synovial fluid of joint, umbilical cord and the eye. It’s a straight chain polymer of D- glucuronic acid and N-acetyl-D-glucosamine (NAG) alternating in the chain. Has and linkages 2. S torage Heteropolysaccharides: Less common, mainly involved I metabolic processes or as precursor for other biological molecules 3. P rotective Heteropolysaccharides: Form protective coatings in bacteria (capsules) example alginates in brown algae.  

97. HEPARIN Act as anticoagulant. Meaning it prevent coagulation of blood by inhibiting the prothrombin thrombin conversion. Composed of D- glucuronic acid units, most of which (7/8) are esterified at C2 and D-glucosamine-N- sulphate unit with O- sulphate at C6. It has alternating linkages and the sulphate content is very high corresponding to about 5-6 molecules per tetrassacharide repeating units.  

98. CHONDROITIN Its of limited distribution, found in cartilage and its also component of cell coats. Its divided into chondroitin sulphate A and chondroitin sulphate B. It has a similar structure to hyaluronic acid except that it contains galactosamine rather than glucosamine. It’s a polymer of -glucuronido-1,3-N-acetyl-D-galactosamine joined by linkages.  

99. DERMATAN SULPHATE Structurally similar to chondroitin sulphate A except that the D-glucuronic acid is replaced by L-iduronic acid and the two linkage involve and glycosidic bonds .  

100. Summary of the polysaccharides