Structural Biochemistry: Carbohydrates PDF

STRUCTURAL BIOCHEMISTRY CARBOHYDRATES Rufaida A. Mahing, MD October 7, 2024 Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides Outline: 1. Definition 2. Classification 3. Character...

STRUCTURAL BIOCHEMISTRY CARBOHYDRATES Rufaida A. Mahing, MD October 7, 2024 Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides  are polyhydroxy aldehydes Definition or ketones compounds which yield polyhydroxy aldehydes and ketones upon hydrolysis. are polyhydroxy aldehydes or ketones molecule that contains multiple hydroxyl groups (-OH).  are polyhydroxy aldehydes or ketones aldehyde is an organic compound that contains a carbonyl group (C=O) where the carbon atom is bonded to at least one hydrogen atom. The general formula for an aldehyde is R-CHO, where: – R represents any alkyl or aryl group (or just hydrogen in the case of formaldehyde). – CHO represents the aldehyde functional group.  are polyhydroxy aldehydes or ketones organic compound that contains a carbonyl group (C=O) where the carbon atom is bonded to two other carbon atoms (alkyl or aryl groups). The general formula for a ketone is R-CO-R', where: – R and R' represent alkyl or aryl groups, which can be the same or different. compounds which yield polyhydroxy aldehydes and ketones upon hydrolysis chemical reaction in which a molecule is broken down into two or more smaller molecules by the addition of water (H₂O). Hydrolysis => "splitting with water" compounds which yield polyhydroxy aldehydes and ketones upon hydrolysis Examples: Disaccharides (sucrose and maltose) yield two monosaccharide molecules on hydrolysis. Definition vare polyhydroxy aldehydes or ketones vcompounds which yield polyhydroxy aldehydes and ketones upon hydrolysis.  Carbohydrates are organic biomolecules abundantly distributed in animals and plants. Plants synthesize carbohydrates through photosynthesis, converting sunlight into chemical energy stored in the form of glucose. Excess glucose is converted into starch for long-term energy storage. Animals glucose and glycogen forms of carbohydrates serve as an instant and important source of energy for physiological activities.  Highly specific carbohydrates like ribose, lactose, and galactose serve as structural components of nucleic acid, lipids, and breast milk. Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides  1.Monosaccharides 2.Disaccharides Classification 3.Oligosaccharides 4.Polysaccharides 1. Monosaccharides word “saccharide” is derived from the Greek word “sakkharon” which means “sugar” or “sweet.” simple sugars carbohydrates which cannot be hydrolyzed into more simple sugars  Their molecular formula is [CnH2nOn) – n: is the number of carbon atoms. – H: hydrogen atoms are double the number of carbons (C) – O: number of oxygen atoms is equal to the number of carbons  For example: – Glucose has the formula – C6H12O6 or C₆H₁₂O₆ fitting the general pattern CnH2nOn or CₙH₂ₙOₙ Classification of Monosaccharides 1. Number of Carbon Atoms – monosaccharides can be trioses, tetroses, pentoses, hexoses, and heptoses. 2. Functional Group – monosaccharides containing aldehyde (–CHO) group are called as “aldoses” - those containing ketone (–CO) group are called as “ketoses.” 2. Disaccharides § Carbohydrates which yield two molecules of similar or dissimilar monosaccharides upon hydrolysis § [Cn(H2O)n–1] Example: Examples: Disaccharides (sucrose and maltose) yield two monosaccharide molecules on hydrolysis. 3. Oligosaccharides § Carbohydrates which yield three to ten monosaccharides units upon hydrolysis 4. Polysaccharides § carbohydrates which yield more than ten monosaccharide units upon hydrolysis. § Polysaccharides are also called as glycans. § Their molecular formula is [C6H10O5]n. § Depending on nature of hydrolytic products, polysaccharides are of two types as follows: 1. Homopolysaccharides (Homoglycans) 2. Heteropolysaccharides (Heteroglycans) 1. Homopolysaccharides (Homoglycans) These polysaccharides yield similar monosaccharide units upon hydrolysis. Example: Starch, glycogen, inulin, cellulose 2. Heteropolysaccharides (Heteroglycans) § These polysaccharides yield dissimilar monosaccharide units upon hydrolysis. § Example: Hyaluronic acid, heparin, chondroitin sulfate, keratan sulfate Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides  1. Asymmetric Carbon Atom 2. Vant Hoff’s Rule of “n” for Characteristics of Number of Isomers Monosaccharides 3. Isomerism in Monosaccharides 4. Optical Isomerism 5. Racemic Mixture 1. Asymmetric Carbon Atom § When four dissimilar atoms or groups are attached to a carbon atom, it is called as asymmetric carbon atom or “chiral carbon.” § Monosaccharides contain asymmetric carbon atoms. § Asymmetric carbon is responsible for isomerism in monosaccharides § Isomerism: two or more compounds have the same chemical formula but differ in the arrangement of atoms or the structure ISOMERISM 2. Vant Hoff’s Rule of “n” for Number of Isomers § According to Vant Hoff’s rule of “n.” – The number of isomers in a compound depends on the number of asymmetric carbon atoms in that compound. § The “n” represents number of asymmetric carbon atoms. § Number of isomers in any monosaccharide is given by. § Aldohexose (glucose) has four asymmetric carbon atoms at positions C2, C3, C4, and C5. § So it has 16 isomers (2x2x2x2=16). § Ketohexose (fructose) has three asymmetric carbon atoms at positions C3, C4, and C5. § So it has eight isomers (2x2x2=8). All isomers are not biologically active in body tissues. 3. Isomerism in Monosaccharides § Isomerism is defined as a phenomenon in which compounds having similar molecular formula exhibit difference in their chemical structures. § The word Isomerism is derived from Greek word and it conveys (‘isos means equal and meros means parts). ISOMERISM 3. Isomerism in Monosaccharides § Monosaccharides exhibit isomerism as described below: 1. Stereoisomerism 2. Enantiomers 3. Epimers 4. Anomers 1. Stereoisomerism is a type of isomerism in which compounds have similar molecular formula, but they differ in relative arrangement of atoms or groups in three-dimensional space. § Monosaccharides show stereoisomerism. § Example: Glucose exhibit two forms as d-glucose and l-glucose. § These stereoisomers differ in arrangement of H and OH groups on C5 atom in glucose molecule. The C5 atom in glucose molecule is called as “reference carbon atom” or “penultimate carbon atom” as in Fig. 6.2. Reference or penultimate carbon is the carbon atom adjacent to the last primary alcohol carbon in a compound. § It determines “d” or “l” series of compounds. § In d-glucose, OH group is located on right-hand side in C5 carbon atom. § In l-glucose, position of OH group is reversed in C5 carbon atom as in Fig. 6.2. Aldohexose exhibits 16 stereoisomers. § They exist in “d” and “l” series. There are eight d-aldohexoses as d-allose, d-altrose, d- idose, d-talose, d-gulose, d- glucose, d-galactose, and d-mannose. There are eight l- aldohexoses as enantiomers. 2. Enantiomers § The stereoisomers that are nonsuperimposable and mirror image of each other. § Example: d-Glucose and l-glucose are mirror images and nonsuperimposable molecules. So they are called as enantiomers as in Fig. 6.2. 3. Epimers § Epimers are the isomers which differ from each other in the arrangement of atoms or groups around a single chiral carbon. § Example: d-Glucose and d-galactose differ around C4 atom. d-Glucose and d-mannose differ around C2 atom as in Fig. 6.3. § The process of conversion of one epimer into another in body tissues is called as epimerization. § In the liver, galactose is converted into glucose by epimerase enzyme. 4.Anomers § Anomers are defined as the cyclic monosaccharides which differ from each other in the arrangement of atoms or groups around C1 atom in aldoses and C2 atom in ketoses. § Chiral carbon in anomers is called as “anomeric carbon.” § Anomers are cyclic epimers as in Fig. 6.4. § Example: – d-Glucose exhibits two anomers, namely, α-d- glucose and β-d-glucose. In § α-d-glucose, OH group is below the plane of molecule. In β-d-glucose, OH group is above the plane of molecule. 4. Optical Isomerism § Asymmetric carbon atom confers optical activity to a compound. When a plane polarized light passes through a monosaccharide solution, it rotates the light beam either to right or left depending. § Optical Activity: Enantiomers exhibit optical activity, meaning they can rotate plane-polarized light. One enantiomer will rotate light in a clockwise direction (dextrorotatory, denoted as +) while the other will rotate it counterclockwise (levorotatory, denoted as -). § This property is measured using a polarimeter, which quantifies the degree of rotation and determines the specific rotation of each enantiomer. § Dextrorotatory glucose molecule is represented as (d-glucose) or (+) glucose § Levorotatory glucose is represented as (l-glucose) or (−) glucose § The rotations “d” and “l” represent stereoisomer and optical isomer. § Example: d-Glucose is (+) or dextrorotatory. § It means a glucose molecule with OH group on the right-hand side on C5 carbon atom can rotate a plane polarized light in right-hand direction. § Another example is d-fructose is (−) or levorotatory. 5. Racemic Mixture It is a mixture which contains equal amount of dextrorotatory and levorotatory isomers of a compound. Racemic mixture is represented with prefix (±)- or (dl). A racemic mixture is inactive optically. Its net optical rotation is zero. Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides  Biologically Important Carbohydrates 1. Monosaccharides 1. Trioses 2. Tetroses 3. Pentoses 4. Hexoses 5. Heptoses 1. Trioses § d-glyceraldehyde and dihydroxyacetone phosphate are the important intermediate metabolites in glycolysis cycle § converted into glycerol which is a structural constituent of lipids 2. Tetroses Erythrose 4-phosphate is an intermediate metabolite in hexose monophosphate shunt a precursor for biosynthesis of tryptophan, phenylalanine, and tyrosine amino acids. 3. Pentoses d-Ribose is a structural residue of RNA, NAD, FAD, and coenzyme A. d-2-Deoxyribose is a structural residue of DNA molecule. d-Ribulose and d-xylulose are intermediate metabolites in HMP shunt l-Xylulose is a marker in hereditary disorder called as “pentosuria.” accumulates in the urine of patient. 4. Hexoses 1. D-Glucose 2. D-Galactose 3. D-Fructose 4. D-Mannose 1. D-Glucose d-glucose is a colorless and crystalline monosaccharide. It is readily soluble in water. exists in nature in free state in fruits like grapes found in bound state in cellulose, maltose, and mucopolysaccharides. It is called as grape sugar. physiologically active sugar present in the human body.  Glucose is the chief source of energy for body tissues. Brain cells and erythrocytes utilize glucose exclusively for their energy demand. Glucose is stored in the liver and skeletal muscles in the form of glycogen. d-Glucose is dextrorotatory and also called as “dextrose.” It is a reducing sugar. It forms glucosazone crystals. Their shape resembles cluster of yellow needles. 2. D-Galactose exists in bound form in nature. Galactose is a structural component of mucopolysaccharides, glycoproteins, and compound lipids. It is a structural unit of lactose. In mammary glands, glucose is epimerized into galactose. d-Galactose is dextrorotatory. It is a reducing sugar. It forms galactosazone crystals. Their shape resembles rhombic plates. 3. D-Fructose It is found mainly in fruits and honey. It is called as fruit sugar. It is a colorless and crystalline ketohexose. It is a structural unit of sucrose. It is sweeter than sucrose. d-Fructose is levorotatory and is also called as “levulose.”  d-Fructose exhibits anomerism. The C2 atom in d-fructose is anomeric, and it forms two anomers, namely, α-d-fructose and β-d- fructose.  It is a reducing sugar. It forms glucosazone crystals. Their shape resembles cluster of yellow needles. 4. D--Mannose It is not an essential sugar in the human body. It is biosynthesized from glucose by epimerization. It was extracted from plant “mannans.” It is a structural unit of glycoproteins in the human body. It forms glucosazone crystals. Their shape resembles cluster of yellow needle- shaped crystals.  5. Heptoses vSedoheptulose It is one of the few heptoses existing in nature found in plants of sedum family. Sedoheptulose 7-phosphate is an intermediate metabolite in HMP shunt 2. Disaccharides 1. Lactose 2. Maltose 3. Sucrose 1. Lactose Lactose is called as “milk sugar.” It is a reducing disaccharide § It is composed of d-glucose and d-galactose, these are linked together by beta-1,4 glycosidic bond as in Fig. 6.5. § It forms lactosazone crystals. Their shape resembles cotton ball or hedge-hog as in Fig. 6.10. § It forms lactosazone crystals. § Their shape resembles cotton ball or hedge-hog as in Fig. 6.10. 2. Maltose It is commonly called as malt sugar. It is a colorless and sweet monosaccharide with crystalline structure. It is composed of two molecules of d-glucose linked by alpha-1,4 glycosidic bond s in Fig. 6.6.  It is a reducing disaccharide Human: maltose is produced by enzymatic hydrolysis by amylase on dietary starch. Maltose is hydrolyzed into two glucose moieties by maltase in the gut. It forms maltosazone crystals.  Their shape resembles sunflower petals as in Fig. 6.10. 3. Sucrose called as table sugar or cane sugar as it is present in sugarcane. readily soluble in water. It is sweet in taste. It is a colorless and crystalline disaccharide.  It is composed of d-glucose and d-fructose linked by alpha-d-glucosyl-beta- d-fructoside (alpha-1,2) linkage  Aldehyde and ketone functional groups are linked together in sucrose. It is a nonreducing disaccharide. There is absence of free functional group. It does not form osazone. Its hydrolytic residues are glucose and fructose. Glucose has dextrorotation (+52.5°), while fructose shows levorotation (−92°). Example: Honey contains invert sugar and fructose. 3. Polysaccharides (Glycans) 1. Homopolysaccharides 1. Starch 2. Glycogen 3. Inulin 4. Cellulose 5. Dextran 2. Heteropolysaccharides 1. Starch Occurrence synthesized by green plants as a reserve food material found in different parts of plants like leaves, stem, roots, and fruits Staple foods, namely, potato, rice, wheat, maize, and cassava Starch is the most common dietary source of energy for humans. Starch is made up of amylose and amylopectin. Amylopectin Amylopectin represents about 80% of starch by weight. It has molecular weight around 500,000–600,000. It is insoluble in water. It swells up in water and forms gel-like mass. It shows reddish violet color with iodine solution § Amylopectin is a greatly branched polymer of d-glucose residues. § Main trunk and branches of amylopectin have d-glucose residues linked by alpha-1 → 4 glycosidic bonds. § A branch of d-glucose residues is linked to the main trunk by alpha-1 → 6 glycosidic bond. Hydrolysis of Starch 1. By Action of Alpha-Amylase § Alpha-amylase is found in saliva and pancreatic juice. § Salivary amylase acts at optimum (pH 6.7), and pancreatic amylase acts at optimum (pH 7.1). § The alpha-amylase cleavages alpha-1 → 4 glycosidic bonds randomly within starch molecule. § In the initial stage, enzymatic hydrolysis yields “amylodextrin.” -> shows violet color with iodine solution. § Further hydrolysis of starch yields “erythrodextrin” which shows red color with iodine solution. § More hydrolysis of starch yields “achrodextrin” which does not give any color with iodine solution. § Finally, enzymatic hydrolysis yield maltose. § Alpha-amylase hydrolysis of starch yields a mixture of maltose and a few residues of dextrin. 2. By Action of Beta-Amylase § Beta-amylase is found in sprouted seeds, germinated cereals (called as malt), and almond. § Beta-amylase starts cleavage of alpha-1 → 4 glycosidic bonds from nonreducing end of starch molecule. § Beta-amylase cannot cleavage alpha-1 → 6 glycosidic bonds at branch points in starch. § It results into formation of limit dextrin. § Beta-amylase hydrolysis of starch yields a mixture of maltose and limit dextrin. § Limit dextrin is a large residual polymer of d-glucose residues which is produced during beta-amylase hydrolysis of starch. It cannot be further hydrolyzed. Functions of Starch Starch is the dietary source of energy for humans and higher animals. In the body, starch is hydrolyzed into maltose and ultimately into glucose. 2. Glycogen Occurrence chief reserve food of animal kingdom stored in the liver and skeletal muscles in humans and higher animals. analogous to starch in plants called as “animal starch.” Some fungi, yeast, and bacteria also possess glycogen in their body. Characteristics and Chemical Composition § Glycogen is a white, odorless, and crystalline polymer of d-glucose. § It is poorly soluble in water and forms an opaque solution. § Its molecular weight ranges from 1,000,000 to 5,000,000. § It shows deep red color with iodine solution. § Glycogen is a highly branched polymer of d-glucose residues. § The main trunk of glycogen molecule is made up of d-glucose residues linked by alpha-1 → 4 glycosidic bonds. § Branches of d-glucose residues are linked to the main trunk by alpha-1 → 6 glycosidic bonds as in Fig. 6.9. Functions of Glycogen § Glycogen is the stored food for animals § converted into glucose by glycogenolysis in the liver and skeletal muscles in humans. § Glucose is utilized by body tissues for fulfilling energy demand. 3. Inulin Occurrence § Inulin is found in plants like onion, garlic, dahlia, and dandelion § It is a reserve food of plants. Characteristics and Chemical Composition § It is a white, odorless, and crystalline polymer of d- fructose. § Its molecular weight is 5000. § It does not give color with iodine solution. § Inulin is made up of d-fructose residues linked by beta-(1 → 2) glycosidic bonds. § Inulin is hydrolyzed by inulinase enzyme present in plant tissues. Functions of Inulin § Inulin is not metabolized in the human body. § Inulin does not have any nutritional value for humans. § Inulin is used to estimate glomerular filtration rate (GFR). § It is an indicator of renal function. § Inulin is used to estimate proportion of extracellular fluid (ECF). 4. Cellulose Occurrence § It constitutes 95% of cotton and 5% of wood. § Cellulose is the main structural constituent of cell wall of green plants. Characteristics and Chemical Composition § It is a white, odorless, and crystalline polymer of d-glucose. § It is hydrophilic but insoluble in water. § Its molecular weight ranges from 27,000 to 900,000. § Cellulose is a linear chain polymer composed of d-glucose residues linked by beta-(1 → 4) glycosidic bonds. § The number of d-glucose residues is variable. § Cellulose polymers in cotton and wood are made up of around 10,000 residues and 2000 d-glucose residues, respectively. § When cellulose is treated by mineral acids, it results into formation of “cellobiose.” § It is a reducing disaccharide. § It is made up of two units of d-glucose § linked by beta-(1 → 4) glycosidic bonds. Functions of Cellulose § It is not digested in the human body: absence of cellulose- digesting enzyme § Cellulose does not have any nutritional value for humans. § Cellulose has roughage value for humans. § Ingestion of cellulose in the form of vegetables and fruits increases contents of the large intestine. § Distension of the intestine stimulates peristalsis and helps in evacuation of bowels -> relieves constipation. § Cellulose is digested by termites and ruminants. Termites possess Trichonympha in the gut Ruminants harbor anaerobic bacteria in the large intestine which help in digestion of cellulose by action of cellulase enzyme. 5. Dextran Occurrence § synthesized from sucrose by action of Gram-positive cocci named as Leuconostoc mesenteroides (induce polymerization of glucose residues in sucrose and result into formation of dextran) Characteristics and Chemical Composition § It is a colorless, odorless, and crystalline polymer of glucose. § It is readily soluble in water. § Its molecular weight ranges from 1,000,000 to 2,000,000. § Dextran is a neutral polymer and exhibits high colloidal osmotic pressure. § Dextran is a highly branched chain polymer of d-glucose residues. There is alpha-(1 → 6) glycosidic linkage between d-glucose residues in straight chain. The branch points are attached by alpha-(1 → 3) linkage. Functions of Dextran § Dextran is not metabolized in the body. § used as plasma expander. § It helps to increase volume of plasma. § It is useful to manage hypovolemia due to acute blood loss when blood transfusion is not possible. Heteropolysaccharides (Heteroglycans) § polymers of different monosaccharides. § yield mixture of monosaccharide units on hydrolysis. § called as “heteroglycans.” § This group of glycans is structurally associated with amino sugars and uronic acid. § Therefore, they were described as “glycosaminoglycans” (GAGs). § characterized by formation of slimy and viscous solution. So they are called as “mucopolysaccharides.” Outline: 1. Definition 2. Classification 3. Characteristics of Monosaccharides 4. Biologically Important Carbohydrates 5. Classification of Mucopolysaccharides  Classification of Mucopolysaccharides Classification of Mucopolysaccharides 1. Acidic and Non-sulfated Mucopolysaccharides Hyaluronic Acid 2. Acidic and Sulfated Mucopolysaccharides 1. Keratan Sulfate 2. Chondroitin Sulfate 3. Heparin 3. Neutral Mucopolysaccharides Classification of Mucopolysaccharides 1. Acidic and Non-sulfated Mucopolysaccharides Hyaluronic Acid 2. Acidic and Sulfated Mucopolysaccharides 1. Keratan Sulfate 2. Chondroitin Sulfate 3. Heparin 3. Neutral Mucopolysaccharides  Hyaluronic Acid Occurrence § found in synovial fluid in joints, vitreous humor of the eye, epithelial tissues, connective tissues, brain tissues, and umbilical cord. Characteristics and Chemical Composition It is an acidic mucopolysaccharide at body pH. Its molecular weight is around 5,000,000. Hyaluronic acid exists in free state and in bound state with proteins. It forms a viscous gel with proteins which is a component of extracellular matrix. Hyaluronic acid is a polymer of d-glucuronic acid and N- acetyl glucosamine (NAG) residues. These residues are linked by beta-(1 → 3) and beta-(1 → 4) glycosidic linkages. Upon hydrolysis, it yields equimolar proportion of d- glucuronic acid, N-acetyl glucosamine, and acetic acid in solution. Functions of Hyaluronic Acid an integral structural component of extracellular matrix in tissues. acts as cementing substance in body tissues. acts as shock absorbant and lubricant in joints. forms a viscous gel that fills the intercellular spaces. So it resists the invasion of pathogenic bacteria in tissues. present in high concentration in embryonic tissues. It is helpful in cell migration and formation of granulation tissues. It is necessary for wound repair in embryonic tissues. found in basement membrane of glomerulus. It is helpful in glomerular filtration. Classification of Mucopolysaccharides 1. Acidic and Non-sulfated Mucopolysaccharides Hyaluronic Acid 2. Acidic and Sulfated Mucopolysaccharides 1. Keratan Sulfate 2. Chondroitin Sulfate 3. Heparin 3. Neutral Mucopolysaccharides  1. Keratan Sulfate Occurrence § Keratan sulfate was isolated from the bovine cornea. § It is found in the cornea, cartilage, and bone. Chemical Composition Keratan sulfate is a polymer of disaccharide residues of N-acetyl d-glucosamine and d-galactose. These residues are linked by beta-(1 → 3) linkages. Sulfate residues are present on the C6 of N-acetyl d- glucosamine residues. Uronic acid residue in keratin sulfate is absent.  Types of Keratan Sulfate § It is classified into two types on the basis of its occurrence in body tissues: 1. Keratan Sulfate-I § It is called corneal keratan sulfate. 2. Keratan Sulfate-II § It is also called as non-corneal keratin sulfate. § It is found in cartilage and bone. Functions of Keratan Sulfate Corneal keratan sulfate is an important structural constituent of stroma of human cornea. It is made up of collagen fibers and proteins and glycosaminoglycans. Its deficiency results into macular corneal dystrophy. Non-corneal keratan sulfate is a structural component of cartilages and bone.  2. Chondroitin Sulfate Occurrence § found in bone, cartilage, skin, tendons, and heart valves of humans.  Types and Chemical Composition § Depending on chemical composition, chondroitin sulfate is classified into four types: 1. Chondroitin sulfate A 2. Chondroitin sulfate B 3. Chondroitin sulfate C 4. Chondroitin sulfate D 1. Chondroitin sulfate A § It is a polymer of disaccharide of N-acetyl d-galactosamine and d-glucuronic acid. § The sulfate residues are present on C4 of N-acetyl d- galactosamine. § It is found in cartilages, cornea, and bones. 2. Chondroitin sulfate B § It is a polymer of disaccharide of N-acetyl d-galactosamine and l-iduronic acid. § d-Glucuronic acid undergoes epimerization into l-iduronic acid in chondroitin sulfate B. § The sulfate residues are present on C4 of N-acetyl d- galactosamine. § It is found in human skin, heart valves, blood vessels, lungs, and tendons. Chondroitin sulfate B is called as “dermatan sulfate” due to its presence in the skin. It shows weak anticoagulant property and is also called as “beta-heparin.” 3. Chondroitin sulfate C § It is a polymer of disaccharide of N-acetyl d-galactosamine and d-glucuronic acid. § The structure of chondroitin sulfate C and chondroitin sulfate A resembles each other except the position of sulfate residues. § The sulfate residues are present on C6 of N-acetyl d- galactosamine in chondroitin sulfate C. § It is found in tendons and cartilages. 4. Chondroitin sulfate D § It is a polymer of disaccharide of N-acetyl d-galactosamine and d-glucuronic acid. § The sulfate residues are present on C6 of N-acetyl d- galactosamine and C2 of d-glucuronic acid. § It is found in shark cartilage. Functions of Chondroitin Sulfate § prime structural constituent of ground substance of bone, cartilage, tendon, and skin. § shows weak anticoagulant property. § role in neuronal growth and neuronal repair due to its presence in extracellular matrix in brain tissues. § maintains elasticity and resilience of articulating cartilage in joints. § Dermatan sulfate has a role in wound repair in skin and blood vessels. It is implicated in cardiovascular disease, carcinogenesis, and infection.  3. Heparin Occurrence § isolated from the liver § synthesized by mast cells in the liver § occurs in the blood vessels, lungs, spleen, thymus, and skin. Chemical Composition Heparin is a highly sulfated mucopolysaccharide. It is also called as “alpha heparin.” Its molecular weight varies from 15,000 to 20,000. It is a polymer of disaccharide of d-glucosamine and d- glucuronic acid or l-iduronic acid. These residues are linked by alpha-(1 → 3) linkages.  In d-glucosamine, sulfate residues are present at C2 and C6. The C2 position in d-glucuronic acid or l-iduronic acid is sulfated. In initial stage of heparin polymerization, it contains d- glucuronic acid residues. Later on, about 95% of d-glucuronic acid is replaced by l- iduronic acid through epimerization. Functions of Heparin § stored in granules of mast cells. It is released into blood vessels and act as anticoagulant. § may act as anti-inflammatory in bronchial asthma and ulcerative colitis. Classification of Mucopolysaccharides 1. Acidic and Non-sulfated Mucopolysaccharides Hyaluronic Acid 2. Acidic and Sulfated Mucopolysaccharides 1. Keratan Sulfate 2. Chondroitin Sulfate 3. Heparin 3. Neutral Mucopolysaccharides  Neutral Mucopolysaccharides Blood group substances are glycoprotein. They consist of neutral mucopolysaccharides covalently linked to peptides. They contain carbohydrate residues like N-acetylated galactosamines, N-acetylated glucosamine, fucose, galactose, and sialic acid. Ovalbumin contains neutral mucopolysaccharides linked to peptides.  Rhamnose occurs in nature as deoxy sugar. an exception to other naturally occurring sugars which exist in d-form. Fucose occurs as hexose deoxy sugar. present in insects and mammalian tissues. It is associated with N-acetylated glycans.  Arabinose is an aldopentose and exists in nature predominantly as l- arabinose component of hemicellulose and pectin isolated from gum arabic or acacia plant whose sap gets hardened on exposure to air. Hemicellulose is a heteropolysaccharide present in cell walls of plants along with cellulose made up of glucose, xylose, mannose, galactose, rhamnose, and arabinose. has an amorphous structure unlike cellulose which has crystalline structure.  Mucoprotein is a conjugated protein made up of oligopeptides covalently linked to glucose, arabinose, xylose, mannose, and fucose carbohydrates. Carbohydrate proportion of mucoprotein is more than 4%, and it can range between 10% and 70%. Glycoprotein is a conjugated protein made up of oligopeptides covalently linked to glucose, arabinose, xylose, mannose, and fucose carbohydrates. Carbohydrate proportion of glycoprotein is less than 4%. It is found in plasma membrane of cells. Example: Mucin.  Proteoglycan is a conjugated protein composed of oligopeptides covalently linked to glycosaminoglycan chains. Carbohydrate proportion of proteoglycans is much higher in range between 70% and 90%. Proteoglycans are negatively charged molecules due to presence of sulfate moieties. They represent the main constituent of extracellular matrix in connective tissues. They are of various types depending on the presence of glycosaminoglycans.  Peptidoglycan is also called as “murein.” It is a polymer formed by cross-linking of carbohydrates and oligopeptides. It is made up of repeated residues of N-acetyl glucosamine (NAG) and N-acetylmuramic acid (NAM) covalently linked to oligopeptides. It forms an important constituent of cell wall of bacteria. Thank You!