Carbohydrates

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Carbohydrates

  1. 1. CARBOHYDRATES -Definition -Classification (mono, di, poly saccaharide) -Isomerism -Properties -Forms of carbohydrates.
  2. 2. • The term carbohydrates refers to hydrates of carbon as in the empirical formulas contain approx. one molecule of water per carbon atom. • Carbohydrates are aldehyde or ketone compounds with multiple hydroxyl groups.
  3. 3. • They make up most of the organic matter on earth because of their multiple roles in all forms of life.
  4. 4. • First, Carbohydrates serve as energy stores, fuels, and metabolic intermediates. • Prime fuel for the generation of energy. EX 1: Starch in plants. EX 2: Glycogen in animals.
  5. 5. ATP, the universal currency of free energy, is a phosphorylated sugar derivative.
  6. 6. Second, ribose and deoxyribose sugars form part of the structural framework of DNA and RNA. • The conformational flexibility of these sugar rings is important in the storage and expression of genetic information.
  7. 7. Third, polysaccharides are structural elements in the cell walls of bacteria and plants. EX: Cellulose, the main constituent of plant cell wall, is the most abundant organic compound in the biosphere.
  8. 8. Fourth, carbohydrates are linked to many proteins and lipids. EX: Sugar units of glycophorin give red cells a highly polar anionic coat. EX: In the form of glycoprotein, these are key participants in cell recognition during development.
  9. 9. Classification • Monosaccharide. • Disaccharides • Oligosaccharides • Polysaccharides
  10. 10. MONOSACCHARIDES • Carbohydrates that cannot be hydrolyzed into simpler carbohydrates. • They may be classified as depending upon the number of carbon atoms. • Trioses, • Tetroses, • Pentoses, • Hexoses • Heptoses
  11. 11. Monosaccharides are reduced to sugar alcohols by reduction of aldehyde and ketone groups. • They are used in food made for diabetics as they have half the energy production as sugars because these are poorly absorbed. Ex: Glucose→ galactol
  12. 12. Disaccharide – condensation of two monosaccharide units produces a disaccharides. • The O – glycosidic bond is formed between the monosaccharide units. • Three highly abundant disaccharides are sucrose, lactose and maltose.
  13. 13. • Oligosaccharides – are condensation products of three to ten monosaccharides. EX: Dextran and Dextrins. EX: Integral membrane proteins contain covalently attached oligosaccharides on their extracellular surface.
  14. 14. EX: Secreated proteins like antibodies and clotting factors also contain oligosaccharide units which are either attached via O – glycosidic linkages or N – glycosidic linkages.
  15. 15. Polysaccharides • Condensation products of more than ten monosaccharide units. EX: Starch and glycogen which may be linear or branched polymers. EX: Cellulose (glucose polymer) and inulin (fructose polymer) ↓
  16. 16. MONO SACCHARIDES • Biomedically glucose is the most important monosaccharide. Structure • It’s structure can be projected by Fisher represented both • as a straight chain and • as a cyclic
  17. 17. • These are projected by Haworth structure. • The straight chain accounts for some of the properties of glucose like reduction, oxidation etc.
  18. 18. • A cyclic structure is thermodynamically favoured and accounts for most properties of glucose. • Cyclical structure is formed by reaction between the aldehyde group and a hydroxyl group.
  19. 19. • This structure has carbon atoms in two orientations - (a) axial (b) equatorial axial bonds are nearly per pendicular to the average plane of the ring. Equatorial bonds are parallel to this plan.
  20. 20. The ring structure adopts chair and boat conformations
  21. 21. ISOMERISM • Compounds with same chemical formula with different structural arrangement around a-symmetric carbon atoms. • Isomers depend upon number of asymmetric carbon atoms in a compound.
  22. 22. • The formula to calculate isomers of a compound is 2n where n is the number of a-symmetric carbon atoms. EX: glucose with four asymmetric carbon atoms can form sixteen (16) isomers. EX: Glyceraldehyde has a single asymmetric carbon and so has two isomers.
  23. 23. TYPES • D and L isomerism • Pyranose and furanose ring structure • Alpha and beta anomers • Epimers • Aldose-ketose isomerism
  24. 24. D and L isomerism • Configuration of H and OH groups around the 2nd carbon atom of glyceraldehyde determine the D and L varieties of isomers. • D and L isomers are mirror images of each other and are called enantiomers. • This carbon atom is the reference carbon and is also called penultimate carbon.
  25. 25. • The orientation of the H and OH groups at carbon no.5 in glucose determines whether sugar belongs to D or L series. • When OH group is on the right of this carbon, the sugar is the D isomer. When it is on the left, it is the L-isomer.
  26. 26. • Most monosaccharides occurring in mammals are D sugars. • Our body can metabolize only D-sugars.
  27. 27. Stereoisomer • Having same structural formula but differ in spatial configuration. • No of possible stereoisomers depend upon the no of asymmetric carbon atom. • Formula for no of stereoisomer is 2 n .
  28. 28. • Where n is the no of stereoisomer. • Diastero-isomers depend on the configurational changes on C2, C3 & C4. • It will produce MS like glucose, mannose, galactose etc.
  29. 29. Optical isomerism • The presence of asymmetric carbon atoms also confers optical activity on the compound. • It is rotation of plane polarized when passed through a sugar solution of an isomer.
  30. 30. • If the rotation is towards right then the compound is said to be dextrarotatory (+). • If it rotates to the left then the compound is said to be levorotatory (-).
  31. 31. • The direction of rotation is independent of the structure of the sugar. • Glucose is dextrorotatory and so is at times referred as dextrose. • D glucose is dextrorotatary, represented as D (+). • D-Fructose is levorotatory so is represented as D (-).
  32. 32. • Equimolecular mixture of optical isomers has no net rotation and so are referred as recemic mixture.
  33. 33. Mutarotation • A freshly prepared solution of D-glucose at room temperature has specific rotation of polarized light + 112 degree. • After 12-18 hrs it changes to +52.5 degree.
  34. 34. • It initial crystallization is at 98 degree and than solubalized the specific rotation will be + 19 degree. • Within few hours, it will also change to + 52.2 degree.
  35. 35. • This change in rotation with time is called mutarotation. • It depends on the fact that D-glucose has 2 anomers α and ß.
  36. 36. • At equilibrium 1/3rd mols are α type and 2/3rd are ß variety. • The difference of α and ß forms is dependent on the first carbon atom only.
  37. 37. PURANOSE AND FURANOSE RING STURCTURE • Ring structure of monosaccharides are similar to the ring structures of either • pyran (six-memberd ring) or • furan (a five memberd ring). • In glucose solution 99% is pyranose form.
  38. 38. Alpha and Beta anomers • Cyclization of sugar creates an anomeric carbon generating alpha and beta configuration of the sugar. • These are referred as anomers of each other.
  39. 39. • Alpha and beta are not the mirror images. • Ring structure of aldose is hemiacetal • Ring structure of ketose is hemiketal. • In solution, cyclic structure is retained but isomerism occurs only around C1
  40. 40. • It gives a mixture of α-glucopyranose (38%) and β-glucopyranose (62%). • Less than 0.3% by α and β anomers of glucofuranose. • The specific rotation [α] D is defined as the observed rotation of light of wave length 589 nm passing through 10 cm of a 1g/ml of a sample.
  41. 41. • The specific rotation of α anomers is +112 degrees and β anomers is + 18.7 degrees. This rotation of light keeps changing in a freshly prepared solution.
  42. 42. EPIMERS • Epimers are isomers differing as a result of variations in configuration of the OH and H on carbon atoms 2, 3 and 4 of glucose are known as epimers. • Biologically most important epimers of glucose are mannose (carbon no.2) and galactose (carbon no.4).
  43. 43. • Eight different monosaccharides are produced by this configurational change around C2, C3 and C4. EX : Glucose Idose, Talose, Allose and Altrose etc. • Molecular formula C6H12O6 represents 16 different monosaccharide units due to spatial arrangement.
  44. 44. Aldose-Ketose isomerism • Fructose has the same molecular formula as glucose but differ in its structural formula as fructose has a potential keto group in position no.2 (anomeric carbon of fructose) • Glucose has a potential aldehyde group in position no.1 (anomeric carbon of glucose)
  45. 45. REACTION OF MONOSACCHARIDES Reduction:• Sugars are reduced under specific conditions of pressure and temperature to form alcohol. • Reduction of hydrogen atoms leads to formation of alcohols. • Aldoses form one alcohol. • ketoses forms two alcohols due to appearance of a new a-symmetric carbon atom during the process
  46. 46. • Glucose, fructose and mannose forms 1,2 enediol • Galactose dulcitol • Ribose ribitol • Enediols are highly reactive, so sugars are powerful reducing agents in alkaline medium and form the basis of benedicts test.
  47. 47. • Certain strains of bacteria use these alcohols as source of energy and are used to identify colonies of bacteria. • Presence of these alcohols in tissues cause osmotic imbalance resulting in accumulation of fluid in them, EX; Cataract of lens
  48. 48. Oxidation • Under mild oxidation conditions, Aldehyde group is oxidized to carboxyl group to produce aldonic acid glucose gluconic acid mannose mannonic acid galactose galactonic acid
  49. 49. • when aldehyde group is protected then the molecule is oxidised at the last carbon and CooH group is formed at this carbon to form uronic acid glucose glucoronic acid mannose mannuronic acid galactose galacturonic acid
  50. 50. • Glucoronic acid is used by the body for conjugation with insoluble molecules to make them soluble in water and for synthesis of heteropoly saccharides. • Under strong oxidation conditions the 1st and last carbon atoms are simultaneously oxidized to to form dicarboxylic acids called as saccharic acids glucose glucosaccharic acid mannose mannaric acid galactose mucic acid
  51. 51. FORMATION OF GLYCOSIDES • When a hemi-acetal group is condensed with either an alcohol or phenol group, it forms a glycoside. • Some of the glycosides are important medically as drugs.
  52. 52. • Condensation is between the hydroxyl group of the anomeric carbonof monosaccharide and a second compound that may or may not be another monosaccharide EX glycone or aglycone.
  53. 53. • If the hemiacetal portion is glucose the resulting compound is a glucoside. • If it is a galactose then it is a galactoside and so on. • If the second group is an amine so Nglycosidic bond is formed. EX: bond between adenine and ribose in nucleotides such as ATP
  54. 54. • Glycosides are widely distributed in nature. • a-glycone may be methanol, glycerol, sterol, phenol or a base such as adenine. • Most important are cardiac glycosides which contain steroids as the aglycone.
  55. 55. • Also ouabain is inhibitor of Na-K+ ATpase of cell membranes. • Other glycosides include antibiotics like streptomycin.
  56. 56. Ester formation: • Hydroxyl group of sugar can be esterified to form acetates, propionate, benzoate etc • Sugar phosphate are biologically important in glucose meta as intermediates
  57. 57. Sugar Source Biochemical and Clinical importance D-Ribose Nucleic acids and metabolic intermediate Structural component of nucleic acids coenzymes, including ATP, NAD(P), and flavin coenzymes D-Ribulose Metabolic intermediate Intermediate in the pentose phosphate pathway D-Arabinose Plant gums Constituent of glycoproteins D-Xylose Plant gums, proteoglycans, glycosaminoglycans Constituent of glycoproteins L-Xylulose Metabolic intermediate Excreted in the urine in essential pentosuria
  58. 58. Sugar Source Biochemical Importance Clinical Significance D-Glucose Fruit juices, hydrolysis of starch, cane or beet sugar, maltose and lactose The main metabolic fuel for tissues; “blood sugar” Excreted in the urine (glucosuria) in poorly controlled diabetes mellitus as a result of hyperglycemia D-Fructose Fruit juices, honey, hydrolysis of cane or beet sugar and inulin, enzymic isomerization of glucose syrups for food manufacture Readily metabolized either via glucose or directly Hereditary fructose intolerance leads to fructose accumulation and hypoglycemia D-Galactose Hydrolysis of lactose Readily metabolized to glucose; synthesized in the mammary gland for synthesis of lactose milk. A constituent of glycolipids and glycoproteins Hereditary galactosemia as a result of failure to metabolize galactose leads to cataracts D-Mannose Hydrolysis of plant mannan gums Constituent of glycoproteins
  59. 59. Sugar Composition Source Clinical Significance Isomaltose O-α-D-glucopyranosyl(1→6)- α-Dglucopyranose Enzymic hydrolysis of starch (the branch points in amylopectin) Maltose O-α-D-glucopyranosyl(1→4)- α-Dglucopyranose Enzymic hydrolysis of starch (amylase); germinating cereals and malt Lactose O-α-D-galactopyranosyl(1→4)-β-D-glucopyranose Milk (and many pharmaceutical preparations as a filler) Lack of lactase (alactasia) leads to lactose intolerance – diarrhea and flatulence; may be excreted in the urine in pregnancy Lactulose O-α-D-galactopyranosyl(1→4)-β-D-fructofuranose Heated milk (small amounts), mainly synthetic Not hydrolyzed by intestinal enzymes, but fermented by intestinal bacteria, used as a mild osmotic laxative Sucrose O-α-D-glucopyranosyl(1→2)-β-Dfructofuranoside Cane and beet sugar, sorghum and some fruits and vegetables Rare genetic lack of sucrase leads to sucrose intolerance – diarrhea and flatulence Trehalose O-α-D-glucopyranosyl(1→1)- α -Dglucopyranoside Yeasts and fungi; the main sugar of insect hemolymph
  60. 60. Sucrose (cane sugar) Present in honey and fruits. Hydrolysis of sucrose (O/R +66.5) will produce • Glucose (+52.5) • Fructose (-920). • Products will change dextrorotation to Levorotation-----called invert sugar.
  61. 61. • Enzyme used is invertase. • It is a non-reducing sugar as free sugar groups are not available for reduction present at C4.
  62. 62. Lactose (milk sugar) • Reducing disaccharide. • Hydrolyzed by lactase to form glucose and galactose. • Because of ß glycosidic linkage b/w galactose and glucose. • It can be hydrolyzed by ß glycosidase. • Forms osazone “hedgehog”.
  63. 63. Maltose • Reducing disaccharide. • It forms petal shaped crystals of maltoseosazone. • On hydrolysis it gives 2 glucose residues with α1→4 glycosidic linkage.
  64. 64. • It is a product of salivary amylase action upon starach. • Isomeric form is isomaltose (α1→6). • Partial hydrolysis of glycogen and starch produces isomaltose due to action of oligo- 1 →6 glucosidase.
  65. 65. Polysaccharides • Polymerized products of many MSs. • Classified as • Homopolysaccharides or homoglycans Examples: Starch Glycogen Cellulose
  66. 66. • Heteropolysaccharides or heteroglycans or glycosaminoglycans. Examples • Agar (galactose, glucose and other sugars).
  67. 67. • Hyaluronic acid (repeated units of N-acetyl glucosamine, 4 glucoronic acid) • Heprin (repeated units of sulfated glucosamine, 4L iduronic acid, which is the oxidized form of idose--------a 5 th isomer of glucose).
  68. 68. Starch: • Most important dietary source of CHO. • Has 2 main constituents i.e. • Amylose (13-20%) has a non branching helical structure. • Amylopectin (80-85%) and consist of branched chain composed of 24-30 glucose residues and linkages in the chain at branched point is 1-6.
  69. 69. • Each branch consist of 15-18 glucose units. • A branch is after every 8-9 glucose units. • On hyrdrolysis, it gives glucose.
  70. 70. Glycogen (animal starch) • Stored polysaccharide in animals especially in liver and muscle. • It is more branched and more compact than amylopectin of starch. • Its MW is high. It is therefore exert very little O/P. • Hence liver cell can store glycogen in a small space.
  71. 71. Cellulose • Most abundant organic material in nature. • Made up off glucose units with ß 1→4 linkages. • It has a straight line structure with no branch.
  72. 72. • Cannot be digested in human, as they lack cellulase enzyme. • Herbivores animals and termites can digest cellulose with the help of intestinal bacteria containing cellulase enzymes.
  73. 73. Inulin: • it is composed of D-fructose units with repeated 1-2 linkages. • It is stored CHO present in tubers, onion and garlic etc. • Clinically use to find renal clearance value and GFR.
  74. 74. Dextrans: • Intermediates in hydrolysis of starch. • Highly branched with 1-6 and 1-4 and 1-3 linkages. • Used as plasma expanders I/V for treatment of hypovalemic shock as they donot leak out of BV, due to high MW.
  75. 75. • A- Glycosaminoglycans (mucopolysaccharides, GAGs) • At least seven glycosaminoglycans (GAGS) (hyaluronic acid, chondroitin sulfate, keratan sulfates I and II, heparin, heparan sulfate, and dermatan sulfate) are found in body.
  76. 76. • Structure: A GAG is an unbranched polysaccharide made up of repeating disaccharides with following structural components
  77. 77. • One component a GAG is always an amino sugar, either D‑glucosamine or D‑galactosamine. • The other component of the repeating disaccharide (except in the case of keratan sulfate) is a uronic acid, either L‑glucuronic acid (GlcUA) or its 5'‑epimer, L,‑iduronic acid (IdUA).
  78. 78. • With the exception of hyaluronic acid, all the GAGS contain sulfate groups, either as O‑esters or as N‑sulfate (in heparin and heparan sulfate).
  79. 79. • Definition: Glycosaminoglycans (GAGs) are large complexes of negatively charged heteropolysaccharide chains. They are generally associated with a small amount of protein, forming proteoglycans, which typically consist of over 95 percent carbohydrate.
  80. 80. • The seven GAGs as mentioned in the previous slide differ from each other in a number of the following properties • amino sugar composition • uronic acid composition • linkages between these components • chain length of the disac-charides
  81. 81. • the presence or absence of sulfate groups and their positions of attachment to the constituent sugars • the nature of the core proteins to which they are attached • the nature of the linkage to core protein • their tissue and subcellular distribution • and their bio-logic functions.
  82. 82. • Tissue distribution of GAGs : As the ground or packing substance, they are associated with the structural elements of the tissues such as bone, elastin, and collagen.
  83. 83. • Their property of holding large quantities of water and occupying space, thus cushioning or lubricating other structures, is assisted by the large number of ‑OH groups and negative charges on the molecules, which, by repulsion, keep the carbohydrate chains apart.
  84. 84. • Examples are hyaluronic acid, chondroitin sulfate, and heparin, blood group polysaccharides, blood serum mucoids
  85. 85. Building blocks of GAGs C-5 epimer of glucuronic acid
  86. 86. • Relationship between glycosaminoglycan structure and function • Because of their large number of negative charges, these heteropolysaccharide chains tend to be extended in solution.
  87. 87. • They repel each other and are surrounded by a shell of water molecules. When brought together, they "slip" past each other, much as two magnets with the same polarity seem to slip past each other.
  88. 88. • This produces the "slippery" consistency of mucous secretions and synovial fluid. • When a solution of glycosaminoglycans is compressed, the water is "squeezed out" and the glycosaminoglycans are forced to occupy a smaller volume.
  89. 89. • When the compression is released, the glycosaminoglycans spring back to their original, hydrated volume because of the repulsion of their negative charges. This property contributes to the softness of synovial fluid and the vitreous humor of the eye
  90. 90. Relationship between glycosaminoglycan structure and function When a solution of glycosaminoglycans is compressed, the water is "squeezed out" and the glycosaminoglycans are forced to occupy a smaller volume. When the compression is released, the glycosaminoglycans spring back to their original, hydrated volume because of the repulsion of their negative charges.
  91. 91. • Proteoglycans: When these chains of GAGs are attached to a protein, the compound is known as a proteoglycan, eg., syndecan, betaglycan, serglycin, aggrecan, versican, fibromodulin, etc.
  92. 92. • With the exception of hyaluronic acid, all glycosaminoglycans occur in combination with proteins through covalent bonds forming proteoglycan. The amount of carbohydrate in a proteoglycan is usually much greater than is found in a glycoprotein and may comprise up to 95% of its weight.
  93. 93. • So proteoglycans are proteins that contain covalently linked GAGs. • Proteoglycans vary in tissue distribution, nature of the core protein, attached glycosaminoglycans, and function • The pro­teins bound covalently to glycosaminoglycans are called "core proteins"
  94. 94. General structure of proteoglycan, aggrecan, found in cartilage is shown in the following figure • It is very large (about 2 x 103 kDa), with its overall structure resembling that of a bottle brush. • It contains a long strand of hyaluronic acid (one type of GAG) to which link proteins are attached noncovalently.
  95. 95. General structure of proteoglycan, aggrecan, found in cartilage is shown in the following figure • In turn, link proteins interact noncovalently with core protein molecules from which chains of other GAGs (keratan sulfate and chondroitin sulfate in this case) project.
  96. 96. • Attachment of GAGs to core Proteins: The linkage between GAGs and their core proteins is generally one of three types as below
  97. 97. • An O‑ glycosidic bond between xylose (Xyl) and Ser, a bond that is unique to proteoglycans. This linkage is formed by transfer of a Xyl residue to Ser from UDP‑xylose. Two residues of Gal are then added to the Xyl residue, forming a link trisaccharide, Gal‑ Gal‑ Xyl‑ Ser. Further chain growth of the GAG occurs on the terminal Gal.
  98. 98. • An O‑ glycosidic bond forms between GalNAc (N‑acetylgalactosamine) and Ser (Thr) present in keratan sulfate 11. This bond is formed by donation to Ser (or Thr) of a GalNAc residue, employing UDP‑Ga1NAc as its donor.
  99. 99. • An N‑ glycosylamine bond between GlcNAc (N‑acetylglucosamine) and the amide nitrogen of Asn, as found in N‑linked glycoproteins.
  100. 100. Attachment of GAGs to core Proteins
  101. 101. • Synthesis of acidic sugars • D‑ Glucuronic acid, whose structure is that of glucose with an oxidized carbon 6 (‑ CH20H  ‑ COOH), and its C‑ 5 epimer, L‑ iduronic acid, are essential components of glycosaminoglycans.
  102. 102. • Glucuronic acid is also required in detoxification/conjugation reactions of a number of insoluble compounds, such as bilirubin, steroids, and several drugs. • In plants and mammals (other than guinea pigs and primates, including man), glucuronic acid serves as a precursor of ascorbic acid (vitamin C).
  103. 103. • Synthesis of acidic sugars • Glucuronic acid • Source: Glucuronic acid can be obtained in small amounts from the diet. It can also be obtained from the intracellular lysosomal degradation of glycosaminoglycans, or via the uronic acid pathway.
  104. 104. • Metabolism: The end‑ product of glucuronic acid metabolism in humans is D‑ xylulose 5‑ phosphate, which can enter the hexose monophosphate pathway and produce the glycolytic intermediates glyceraldehyde 3‑ phosphate and fructose 6‑ phophate .
  105. 105. • Active form: The active form of glucuronic acid that donates the sugar in glycosaminoglycan synthesis and other glucuronylating reactions is UDP‑ gIucuronic acid, which is produced by oxidation of UDP‑ glucose
  106. 106. • Synthesis of acidic sugars • L‑ Iduronic • Synthesis of L‑ iduronic acid residues occurs after D‑ glucuronic acid has been incorporated into the carbohydrate chain. • Uronosyl 5‑ epimerase causes epimerization of the D‑ to the L‑ sugar.
  107. 107. Synthesis of acidic sugars
  108. 108. Synthesis of acidic sugars
  109. 109. Synthesis of amino sugars
  110. 110. • Synthesis of amino sugars • Amino sugars are essential components of glycosaminoglycans, gly­coproteins, glycolipids, and certain oligosaccharides, and are also found in some antibiotics.
  111. 111. • The synthetic pathway of amino sugars is very active in connective tissues, where as much as twenty percent of glucose flows through this pathway.
  112. 112. • Synthesis of amino sugars • N‑ Acetylglucosamine (glcNAc) and N‑ acetylgalactosamine (gaINAc): • The monosaccharide fructose 6‑ phosphate is the precursor of gIuNAc, gaINAc, and the sialic acids, including N‑ acetyl­neuraminic acid (NANA, a nine‑ carbon, acidic monosaccharide).
  113. 113. • In each of these sugars, a hydroxyl group of the precursor is replaced by an amino group donated by the amino acid, glutamine. • The amino groups are almost always acetylated.
  114. 114. • The UDP‑ derivatives of gIuNAc and gaINAc are the activated forms of the monosaccharides that can be used to elongate the carbohydrate chains.
  115. 115. • 2. N‑ Acetylneuraminic acid: N‑ Acetylneuraminic acid (NANA) is a member of the family of sialic acids, each of which is acylated at a different site. These compounds are usually found as terminal carbohydrate residues of oligosaccharide side chains of glycopro­ teins, glycolipids, or, less frequently, of glycosaminoglycans.
  116. 116. • The carbons and nitrogens in NANA come from N‑ acetylman­nosamine and phosphoenolpyruvate (an intermediate in the gly­colytic pathway, see p. 100). [Note: Before NANA can be added to a growing oligosaccharide, it must be converted into its active form by reacting with cytidine triphosphate (CTP).
  117. 117. The enzyme N­ acetylneuraminate‑ CMP‑ pyrophosphoryl ase removes pyrophos­phate from the CTP and attaches the remaining CMP to the NANA. This is the only nucleotide sugar in human metabolism in which the carrier nucleotide is a monophosphate.]
  118. 118. • Synthesis of amino sugars • 2. N‑ Acetylneuraminic acid: • N‑ Acetylneuraminic acid (NANA) is a member of the family of sialic acids, each of which is acylated at a different site.
  119. 119. • These compounds are usually found as terminal carbohydrate residues of oligosaccharide side chains of glycoproteins, glycolipids, or, less frequently, of glycosaminoglycans.
  120. 120. • The carbons and nitrogens in NANA come from N‑ acetylmannosamine and phosphoenolpyruvate (an intermediate in the glycolytic pathway, see p. 100). [Note: Before NANA can be added to a growing oligosaccharide, it must be converted into its active form by reacting with cytidine triphosphate (CTP).
  121. 121. • The enzyme N­ acetylneuraminate‑ CMP‑ pyrophosphor ylase removes pyrophosphate from the CTP and attaches the remaining CMP to the NANA. This is the only nucleotide sugar in human metabolism in which the carrier nucleotide is a monophosphate.
  122. 122. Summary of structures of glycosaminoglycans and their attachments to core proteins. Chondroitin sulfate link Hyluronic acid link Keratan sulfate link Heparan sulfate link Dermatan sulfate link Heparin link
  123. 123. GIcUA, D‑glucuronic acid; IdUA, L‑iduronic acid; GIcN, D‑glucosamine; D‑galactosamine; Ac, acetyl; GaIN, Gal, D‑galactose; Xyl, D‑xy­lose; Ser, L‑serine; Thr, L‑threonine; Asn, L‑asparagine; Man, D‑mannose; NeuAc, N‑acetylneuraminic acid
  124. 124. MUCOPOLYSACCHARIDES
  125. 125. • 1- Hyluronic acid • Occurrence: It is present in bacteria and is widely distributed among various animals and tissues, including synovial fluid, the vitreous body of the eye, cartilage, and loose connective tissues.
  126. 126. • As its solution is highly viscous so it occurs in the joints of animas for lubrication. In tissues it forms an important part of the intercellular cement substance and resists penetration by bacteria.
  127. 127. • Effect of enzymes (hyaluronidases): These enzymes break hyaluronie acid. These enzymes are found in certain bacteria, stings of bees, and snake venom. In humans these enzymes also occur in testes, seminal fluid, urine, plasma, synovial fluid and other tissues.
  128. 128. • Enzyme present in bacteria tends to destroy the intercellular hyaluronic acid barrier and permits the invading agent to penetrate tissues; the enzyme is therefore also .called the spreading factor.
  129. 129. • In humans, the presence of this enzyme in the seminal fluid is thought to facilitate fertilization of the ovum. • The preparations of this enzyme are clinically used to increase the absorption of subcutaneously administered fluid.
  130. 130. • Some other functions of hyluronic acid • It is present in high concentration in embryonic tissues and is thought to play an important role in permitting cell migration during morphogenesis and wound repair.
  131. 131. • Its ability to attract water into the extra cellular matrix and thereby "loosen it up". • The high concentrations of hyaluronic acid and chondroitin sulfates present in cartilage contribute to its compressibility.
  132. 132. • Chemically it is a substance of a high molecular weight and consists of alternating residues of N‑ acetylglucosamine and glucuronic acid.
  133. 133. β(14) β(13)
  134. 134. • 2­ Chondroitin sulfates • Occurrence: In In body these are the most abundant glycosaminoglycans. These are found in combination with protein in the ground substance of tissues like cartilage and at sites of calcification in endochondral bone
  135. 135. • Types: There are several types of chondroitin sulfates like A, B, C, and D. • Structure: These consist of a large number alternating units of hexosamine (like N‑acetylgalactosamine) 4‑ (or 6‑) sulfate and uronic acid ( like glucuronic acid or iduronic acid). The structure of chondroitin sulfate D is as follows
  136. 136. • Uronic acid may also be sulfated • Chondroitin sulfate B has a weak anticoagulant activity, that is why it is β­heparin Link Link
  137. 137. 2­ Chondroitin sulfates
  138. 138. 3-Heparin • Structure: The repeating disaccharide contains glucosamine (GlcN) and either of the two uronic acids. Most of the amino groups of the GlcN residues are N‑sulfated, but a few are acetylated. The GlcN also carries a C6 sulfate ester.
  139. 139. • Occurrence: Heparin is found in the granules of mast cells and also in liver, lung, and skin. • The protein molecule of the heparin proteoglycan is unique, consisting exclusively of serine and glycine residues.
  140. 140. 3-Heparin
  141. 141. • Functions of heparin • It is an important anticoagulant. • It binds with factors IX and XI but its most important interaction is with plasma antithrombin III. The 1:1 binding of heparin to this plasma protein greatly accelerates the ability of the latter to inactivate serine proteases, particularly thrombin.
  142. 142. • The binding of heparin to lysine residues in antithrombin III appears to induce a conformational change in this protein that favors its binding to the serine proteases like thrombin. • Heparin can also bind specifically to lipoprotein lipase present in capillary walls, causing a release of this enzyme into the circulation.
  143. 143. • 4- Heparan sulfate • This molecule is present on many cell surfaces (serving as receptors so it may participate in the mediation of cell growth and cell-cell communication) as a proteoglycan and is extracellular. It contains GlcN with fewer N‑sulfates than heparin, and unlike heparin, its predominant uronic acid is GlcUA.
  144. 144. • This proteoglycan is also found in the basement membrane of the kidney, along with type IV collagen and laminin, where it plays a major role in determining the charge selectiveness of glomerular filtration.
  145. 145. • 5- Dermatan sulfate • This substance is widely distributed in animal tissues. Its structure is similar to that of chondroitin sulfate, except that in place of a GlcUA in β‑1,3 linkage to GaINAC, it contains an IdUA in an α‑1,3 linkage to GalNAC. • Dermatan sulfate contains both IdUAGalNAc and GlcUA‑GaINAc disaccharides
  146. 146. • 6,7- Keratan sulfate I and II • Keratan sulfates consist of repeating Gal‑GlcNAc disaccharide units containing sulfate attached to the 6' position of GlcNAc or occasionally of Gal.
  147. 147. • Type I is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein as shown in above structure link.
  148. 148. • Functions of kertan sulfate I and dermatan sulfate • These are present in the cornea. They lie between collagen fibrils and play a critical role in corneal transparency. • Changes in proteoglycan composition found in corneal scars disappear when the cornea heals.
  149. 149. • The presence of dermatan sulfate in the sclera may also play a role in maintaining the overall shape of the eye. • Keratan sulfate I is also present in cartilage.
  150. 150. 6,7- Keratan sulfate I and II
  151. 151. Major properties of glycosaminoglycans
  152. 152. • Functions of heparin • It is an important anticoagulant. • It binds with factors IX and XI but its most important interaction is with plasma antithrombin III. The 1:1 binding of heparin to this plasma protein greatly accelerates the ability of the latter to inactivate serine proteases, particularly thrombin.
  153. 153. • The binding of heparin to lysine residues in antithrombin III appears to induce a conformational change in this protein that favors its binding to the serine proteases like thrombin. • Heparin can also bind specifically to lipoprotein lipase present in capillary walls, causing a release of this enzyme into the circulation.
  154. 154. • Some clinical considerations • Enzymes of degradation – Both exo‑ and endoglycosidases degrade GAGS, Like most other biomolecules, GAGs are subject to turnover, being both synthesized and degraded.
  155. 155. • The deficiencies of these enzymes result in their non‑degradation leading to accumulation; causing several pathological conditions that are collectively called mucopolysaccharidoses. That may involve cornea, nervous tissues, spleen, liver, joints, heart valves and coronary arteries,
  156. 156. • Arthritis: In various types of arthritis, proteoglycans may act as autoantigens, thus contributing to the pathologic features of these conditions.
  157. 157. • Aging: The amount of chondroitin sulfate in cartilage diminishes with age, whereas the amounts of keratan sulfate and hyaluronic acid increase. These changes may contribute to the development of osteoarthritis.
  158. 158. • Changes in the amounts of certain GAGS in the skin are also observed with age and help to account for the characteristic changes noted in this organ in the elderly.
  159. 159. • DEGRADATION OF GLYCOSAMINOGLYCANS • Glycosaminoglycans are degraded in lysosomes, which contain hydrolytic enzymes that are most active at a pH of approximately 5.
  160. 160. • The low pH optimum is a protective mechanism that prevents the enzymes from destroying the cell should leakage occur into the cytosol where the pH is neutral.
  161. 161. • With the exception of keratan sulfate, which has a half‑ life of greater than 120 days, the glycosaminogly- cans have a relatively short half‑ life, ranging from about three days for hyaluronic acid to ten days for chondroitin and dermatan sulfate.
  162. 162. • DEGRADATION OF GLYCOSAMINOGLYCANS • Phagocytosis of extracellular glycosaminoglycans
  163. 163. • Because glycosaminoglycans are extracellular or cell‑ surface compounds, they must be engulfed by an invagination of the cell membrane (phagocytosis), forming a vesicle inside of which the glycosaminoglycans are to be degraded.
  164. 164. • This vesicle then fuses with a lysosome, forming a single digestive vesicle in which the glycosaminoglycans are efficiently degraded
  165. 165. • DEGRADATION OF GLYCOSAMINOGLYCANS • Lysosomal degradation of glycosaminoglycans • The lysosomal degradation of glycosaminoglycans requires a large number of acid hydrolases for complete digestion.
  166. 166. • First, the polysaccharide chains are cleaved by endoglycosidases, producing oligosaccharides.
  167. 167. • Further degradation of the oligosaccharides occurs sequentially from the non‑ reducing end of each chain, the last group (sulfate or sugar) added during synthesis being the first group removed. • Examples of some of these enzymes and the bonds they hydrolyze are shown in the figure on next slide.
  168. 168. Synthesis of acidic sugars
  169. 169. • The mucopolysaccharidoses • The mucopolysaccharidoses are hereditary disorders that are clinically progressive. They are characterized by accumulation of glycosaminoglycans in various tissues, causing varied symptoms, such as skeletal and extracellular matrix deformities, and mental retardation.
  170. 170. • Mucopolysaccharidoses are caused by a deficiency of one of the lysosomal hydrolases normally involved in the degradation of heparan sulfate and/or dermatan sulfate (shown in figure on previous slide).
  171. 171. • This results in the presence of oligosaccharides in the urine, because of incomplete lysosomal degradation of glycosaminoglycans.
  172. 172. • These fragments can be used to diagnose the specific mucopolysaccharidosis, namely by identifying the structure present on the nonreducing end of the oligosaccharide.
  173. 173. • The mucopolysaccharidoses • That residue would have been the substrate for the missing enzyme. • Diagnosis is confirmed by measuring the patient's cellular level of lysosomal hydrolases.
  174. 174. • Children who are homozygous for one of these diseases are apparently normal at birth, then gradually deteriorate. • In severe cases, death occurs in childhood. • All of the deficiencies are autosomal and recessively inherited except Hunter syndrome, which is X‑ linked.
  175. 175. • Bone marrow transplants are currently being used successfully to treat Hunter syndrome; the transplanted macrophages produce the sulfatase needed to degrade glycosaminoglycans in the extracellular space.
  176. 176. • The mucopolysaccharidoses • Some of the lysosomal enzymes required for the degradation of glycosaminoglycans also participate in the degradation of glycolipids and glycoproteins.
  177. 177. Hunter Syndrome • Induronate sulphatase deficiency • X-linked • Wide range of severity. • No corneal clouding but physical deformity • Mental retardation is mild to severe • Degradation of Heparan Sulphate and dermatan sulphate is affected.
  178. 178. Hurler’s Syndrome • Alpha-L-Iduronidase deficiency • Corneal clouding, mental retardation dwarfing, upper Airway obstruction • Coronary artery deposition leads to ischemia and early death • Degradation of Heparan sulphate and Dermatan Sulphate is effected. • Can be treated by Bone Marrow transplant before 18 months of life
  179. 179. San Fi Lippo Syndrome (MPS-III) Types – A, B, C, D • Four enzymatic steps are necessary to remove N-sulphated and N-acetylated glucosamine residues from Heparan Sulphate
  180. 180. Type A: Heparan Sulfamidase deficiency Type B: N-Acetyl glucosulphatase deficiency Type C: Glucosamine-N-Acetyl transferase deficiency. Type D: N-Acetyl glucosamine-6-sulphatase deficiency. Severe nervous system disorders. Mental retardation
  181. 181. SLY Syndrome MPS VII • Beta-Glucuronidase deficiency • Hepatomegaly, splenomegaly, skeletal deformity, short stature, corneal clouding, mental deficiency • Degradation of dermatan sulphate and Heparan sulphate are affected
  182. 182. • Therefore, an individual suffering from a specific mucopolysaccharidosis may also have a lipidosis or glycoprotein‑ oligosaccharidosis.]
  183. 183. Summary of functions of glycosaminoglaycans HA, hyaluronic acid; CS, chondroitin sulfate; KS I, keratan sulfate I; DS, dermatan sulfate; HS, heparan sulfate.
  184. 184. • Act as structural components of the extracellular (EC) matrix • Have specific interactions with collagen, elastin, fibronectin, laminin, and other proteins such as growth factors • As polyanions, bind polycations and cations • Contribute to the characteristic turgor of various tissues
  185. 185. • Act as sieves in the EC matrix • Facilitate cell migration (HA) • Have role in compressibility of cartilage in weight‑bearing (HA, CS) • Play role in corneal transparency (KS I and DS) • Have structural role in sclera (DS)
  186. 186. • Act as anticoagulant (heparin) • Are components of plasma membranes, where they may act as receptors and participate in cell adhesion and cell-cell interactions (eg, HS)
  187. 187. • Determine charge‑selectiveness of renal glomerulus (HS) • Are components of synaptic and other vesicles (eg, HS)
  188. 188. Peptidoglycan Forms the cell walls of bacteria. A complex polysaccharide of alternating Nacetylglucosamine (or NAG) and Nacetylmuramiic acid (or NAM) connected by β(1→4) glycosidic bonds with short peptides bridging the polysaccharide chains.
  189. 189. Peptidoglycan
  190. 190. • Peptidoglycan froms the cell wall of bacteria, capsular antigens, microbial toxins, and procoagulant substances produced by microbial pathogens may all contribute to the pathogenesis of sepsis.
  191. 191. • It has been observed that peptidoglycan, like teichoic acid and other components of gram-positive bacteria, may interact with CD14 molecules and activate inflammatory cells in a manner similar to that of bacterial endotoxin.
  192. 192. • The wall protects bacterial cells from osmotic rupture, which would result from the cell's usual marked hyperosmolarity (by up to 20 atm) relative to the host environment. • The structure conferring cell-wall rigidity and resistance to osmotic lysis in both gram-positive and -negative bacteria is
  193. 193. • Peptidoglycan. • Chemotherapeutic agents directed at any stage of the synthesis, export, assembly, or cross-linking of peptidoglycan lead to inhibition of bacterial cell growth and, in most cases, to cell death.
  194. 194. • Peptidoglycan is composed of • a backbone of two alternating sugars, Nacetylglucosamine and N-acetylmuramic acid; • a chain of four amino acids that extends down from the backbone (stem peptides); and • a peptide bridge that cross-links the peptide chains.

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