Carbohydrate structure


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Carbohydrate structure

  1. 1. Carbohydrates chemistry Dr : Abdel naser Badawy
  2. 2. ‐ Carbohydrates are organic molecules found in nature,  constituting one of the four major classes of biomolecules.  ‐‐ The other three are proteins, nucleic acids and lipids. -- Saccharides (saccharo is Greek for ―sugar)
  3. 3. • Carbohydrates are aldehyde or ketone compounds with multiple hydroxyl groups. • The basic molecular formula (C.H2O)n where n = 3 or more. • The term ―carbohydrate comes from the observation that when you heat sugars, you get carbon and water (hence, hydrate of carbon).
  4. 4. Classification  They are classified according to the number of structural units into: 1‐Monosaccharides= They are the simplest carbohydrates that can not  be hydrolysed into simpler units. 2‐ Disaccharides= produce 2 molecules of monosaccharide on  hydrolysis. 3‐ Oligosaccharides= produce three to ten monosaccharide units on  hydrolysis 4‐ Polysaccharides= : produce more than 10 monosaccharide units on  hydrolysis
  5. 5. Monosaccarides-1 • * Def : They are the simplest carbohydrate unites which can not be hydrolyzed to a simpler form • * General formula: (CH2O)n n≥3
  6. 6. :* Nomenclature • 1- According to active group in the sugar: – If monosaccharide contains aldehyde group (CHO) → it's called aldose. – And if contain ketone group (c=o) → it's called ketose.
  7. 7. According to the number of carbon atoms (n):‐2 If sugar contains  3 carbons → it's called triose,  4c→ tetrose 5c→ pentose            6c→ hexose 7c→ heptose
  8. 8. Three Carbon Four Carbon By combining the two methods , we find that:-3 3c-Aldotriose -ketotriose 4c-Aldotetrose -ketotetrose 5c-Aldopentise -ketopentose 6c-Aldohexose -ketohexose
  9. 9. Five Carbon Six Carbon
  10. 10. The structure of glucose can be represented in one of the  following ways: 1.The straight – chain (open ‐ chain) structural formula : Aldohexose can account for some of the properties of glucose, but  can not explain some reaction   D-glucose
  11. 11. 2. The cyclic structure accounts for the remainder of the chemical  properties of glucose. This cyclic structure can be represented in two  forms: a. Fischer projection formula :where the aldehyde group reacts with  an alcohol group on the same sugar to form a hemiacetal ring. C H – C – OH    HO – C – H  H – C – OH   H – C  CH2OH   α‐D‐Glucopyranose H    OH O C H – C – OH    HO –C – H  H – C – OH   H – C  CH2OH   β ‐D‐Glucopyranose oH H O
  12. 12. b. Haworth formula: Where the cyclic structure is represented in pyranose (six – membered) and  furanose (five – membered) rings resembling pyran and furan rings.  Here oH and H written above and below instead of Right and left  so what is on  Right  → below                     left → above  except last carbon (which close the ring) in which   left →below                                                      Right →above α‐D‐Glucopyranose
  13. 13. An aldehyde or ketone can react with an alcohol in a 1:1 ratio to yield a hemiacetal or hemiketal, respectively, creating a new chiral center at the carbonyl carbon Hemiacetals or Hemiketals
  14. 14. :c) Boat and chair forms represents the three dimensional configuration of sugar in nature.
  15. 15. formshaworthFructose in open chain & 
  16. 16. carbon, AsymmetricAnomeric carbon):chiralcarbon atom ( • It is that carbon atom attached to four different groups or atoms. • Formation of a ring results in the creation of an anomeric carbon at carbon 1 of an aldose or at carbon 2 of a ketose.
  17. 17. Reducing sugars • If the oxygen on the anomeric carbon (the carbonyl group) of a sugar is not attached to any other structure, that sugar is a reducing sugar. • Only the state of the oxygen on the anomeric carbon determines if the sugar is reducing or nonreducing—the other hydroxyl groups on the molecule are not involved
  18. 18. Reducing sugars • A reducing sugar can react with chemical reagents (for example, Benedict's solution) and reduce the reactive component, with the anomeric carbon becoming oxidized.
  19. 19. Any compound having one or more asymmetric carbon atom  shows two properties: 1. Optical activity. 2. Stereoisomerism 
  20. 20. Optical activity-1 • Def. It is the ability of the compound to rotate plane polarized light to the right or to the left. • If the compound rotates plane polarized light to the right, it is called dextrorotatory, d or (+). • If it rotates plane polarized light to the left, it is called levorotatory, l or (-).
  21. 21. • The direction of rotation is independent of the stereochemistry • of the sugar, so it may be designated D(−), D(+), L(−), or L(+). • For example, the naturally occurring form of fructose is the D(−) isomer.
  22. 22. •• dextrorotatorydextrorotatory sugar (d or +):sugar (d or +): glucose,glucose, galactosegalactose and starchand starch •• levorotatorylevorotatory sugar (l orsugar (l or --):): fructosefructose and invert sugarand invert sugar..
  23. 23. 2‐ Stereoisomerism  Compound  that  have  the  same  structural  formula  but  differ  in  spatial  configuration  are  known  as  stereoisomers and  the  phenomenon is called stereoisomerism.   The number of possible isomers of a compound depends on the  number of asymmetric carbon atoms (n) and is equal to 2n.   Glucose, with four asymmetric carbon atoms, has 16 isomers. 
  24. 24. • The more important types of isomers include – D and L isomers, – pyranose and furanose ring structures, – alpha and beta anomers, – epimers and – aldose-ketose isomers.
  25. 25. IsomersIsomers Are compounds which have the same molecularAre compounds which have the same molecular weight, same percentage composition, and differweight, same percentage composition, and differ in their physical and chemical their physical and chemical properties. -- StereoisomersStereoisomers: are compounds that have the: are compounds that have the same structural formula but differ in spatialsame structural formula but differ in spatial configuration (arrangement of atoms and groupsconfiguration (arrangement of atoms and groups of atoms in space around the asymmetricof atoms in space around the asymmetric carbon(scarbon(s) i.e. different configuration).) i.e. different configuration).
  26. 26. 1. D and L isomers ):enantiomers( • A special type of isomerism is found in the pairs of structures that are mirror image of each other. • These mirror images are called enantiomers and the two members of the pair are designated as a D and an L-sugar.
  27. 27. • A monosaccharide is designated D if the hydroxyl group on the highest numbered asymmetric carbon= prelast carbon is drawn to the right as in D- glyceraldehyde and L if the hydroxyl group on the highest numbered asymmetric carbon is drawn to the left as in L- glyceraldehyde.
  28. 28. ‐ The  majority of the sugars in humans are D‐sugars.  ‐ Two exceptions are L‐fucose (in glycoproleins) and L‐iduronic acid  (in glycosaminoglycans).
  29. 29. ring structures: furanoseand Pyranose2.  The   monosaccharides are  either pyran (a six‐membered ring) or furan (a five‐membered ring).  For glucose in solution, more than 99% is in the pyranose form.
  30. 30. :anomers3. Alpha and beta  The ring structure of an aldose is a hemiacetal, since it is  formed by combination of an aldehyde and an alcohol group.  Similarly, the ring structure of a ketose is a hemiketal. The cyclic  structure is retained in solution, but isomerism (C6H12O6) occurs  about position 1, the carbonyl or anomeric carbon atom, to give  a mixture of α‐glucopyranose (38%) and β‐glucopyranose (62%). 
  31. 31. • The cyclic α and β anomers of a sugar in solution are in equilibrium with each other, and can be spontaneously interconverted (a process called mutarotation)
  32. 32. : Epimers4.  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, the most important epimers of  (C6H12O6) glucose are mannose and galactose, formed by  epimerization at carbons 2 and 4, respectively. 
  33. 33. Epimers of glucose D- glucose D- galactose Epimer at C4 D- mannose Epimer at C2
  34. 34. isomerism: ketose‐Aldose5.  Fructose has the same molecular formula as glucose  (C6H12O6) but differs in its structural formula, since there is  keto group in position 2, the anomeric carbon of fructose, whereas  there is  aldehyde group in position 1, the anomeric carbon of  glucose
  35. 35. Are Physiologically Important:MonosaccharidesMany  xylose, ribuloseribose, e.g:Pentoses1  , fructose, mannosegalactoseglucose, : Hexoses‐2 ) are formed as metabolic sedoheptulose(carbon sugar ‐seven‐3 intermediates in  the pentose phosphate pathway. g carboxylic acid derivatives of glucose are important, includin‐4 formation and in glucuronide(for glucuronate‐Da.  glycosaminoglycans)  )glycosaminoglycans(in iduronate‐Lb.  acid pathway)theuronic(an intermediate in gulonate‐Lc. 
  36. 36. Derived Sugars Sugars:Deoxy1.  Lack an Oxygen Atom =Deoxy sugars are those in which a hydroxyl  group has  been replaced by hydrogen.   Examples:  a. deoxyribose in DNA.  b. L‐fucose occurs in glycoproteins. c. 2‐deoxyglucose is used experimentally as an inhibitor of glucose  metabolism..
  37. 37. ):Hexosamines2. Amino Sugars ( Are compounds in which OH at C2 is replaced by NH2  1. D‐glucosamine, a constituent of hyaluronic acid ,  2. D‐galactosamine(chondrosamine), a constituent of chondroitin;  3.  Several antibiotics (eg, erythromycin) contain amino sugars  believed to be important for their antibiotic activity Galactosamine
  38. 38. 3.Sugar acids 1.1. Produced by oxidation ofProduced by oxidation of carbonyl carbon to carboxyliccarbonyl carbon to carboxylic 2.2. Or by oxidation of last hydroxylOr by oxidation of last hydroxyl carbon to carboxylic group.carbon to carboxylic group. 3.3. Or by oxidation of both.Or by oxidation of both.
  39. 39. 1.Aldonic1.Aldonic CHO C OHH C HHO C OHH C OHH CH2OH COOH C OHH C HHO C OHH C OHH CH2OH brominewater, O2 D-GluconicacidD-Glucose
  40. 40. UronicUronic--22 CHO C OHH C HHO C OHH C OHH CH2OH CHO C OHH C HHO C OHH C OHH COOH Dil. Nitricacid D-GlucuronicacidD-Glucose H2O2
  41. 41. AldaricAldaric--33 CHO C OHH C HHO C OHH C OHH CH2OH COOH C OHH C HHO C OHH C OHH COOH Conc. Nitric acid D-GlucaricacidD-Glucose O2
  42. 42. Glycoside Formation • The hemiacetal and hemiketal forms of monosaccharides can react with alcohols to form acetal and ketal structures called glycosides. The new carbon-oxygen bond is called the glycosidic linkage.
  43. 43. AcetalGlycosides= The OH of anomeric carbon of monosaccharides can react with either:  1‐ Nitrogen of amines (The anomeric carbon atom of sugar can be  linked to the nitrogen atom of an amine by N‐ glycosidic bond) e.g OH  of ribose linked to nitrogen  of nitrogenous base to form nucleotides. 
  44. 44. OH of other-2 compound : • A- May be carbohydrate ( Monosaccharides can be linked to each other by O- glycosidic bonds to form disaccharides, oligosaccharides and polysaccharides). • (monosaccharide+ monosaccharide)=hemiacetal+hemia cetal=acetal. • b- May be non carbohydrate e.g glycolipid, glycoprotein. • The non carbohydrate component of a glycoside is called aglycone.
  45. 45. O- and N-glycosides • If the group on the non- carbohydrate molecule to which the sugar is attached is an -OH group, the structure is an O-glycoside • All sugar-sugar glycosidic bonds are O- type linkages
  46. 46. O- and N-glycosides • If the group is an -NH2 , the structure is an N- glycoside – purines and pyrimidines (found in nucleic acids), – aromatic rings (such as those found in steroids and bilirubin), – proteins (found in glycoproteins and glycosaminoglycans),
  47. 47. Naming glycosidic bonds • Glycosidic bonds between sugars are named according to – numbers of the connected carbons (1-4, 1-6), and – position of the anomeric hydroxyl group of the sugar involved in the bond.
  48. 48. Naming glycosidic bonds • this anomeric hydroxyl group is in the α configuration, the linkage is an α-bond. • If it is in the β configuration, the linkage is a β-bond.
  49. 49. Naming glycosidic bonds • Lactose, for example, is synthesized by forming a glycosidic bond between carbon 1 of β-galactose and carbon 4 of glucose. – The linkage is, therefore: β(1 →4) glycosidic bond. • Because the anomeric end of the glucose residue is not involved in the glycosidic linkage it (and, therefore, lactose) remains a reducing sugar.
  50. 50. Naming of  O‐ glycosidic bond() carbohydrate and carbohydrate ‐ Glycosidic bonds between sugars are named according to: 1‐ The numbers of the connected carbons  2‐ The position of the anomeric hydroxyl group of the sugar. If the anomeric hydroxyl group is in α configuration the link is α‐ bond and if it’s   in β, the link is β‐ bond. Examples In lactose β 1 of galactose bind to C4 of glucose by  β 1  → 4  galactosidic bond.
  51. 51. Examples of glycosides: 1‐ Disaccharides as maltose, lactose and sucrose 2‐ Polysaccharides. 3‐ Glycolipids. 4‐Glycoproteins.(may be O‐ or N‐ glycosidic link) 5‐Nucleotides as ATP, GTP, UTP where aglycon is purine or  pyrimidine bases      (N‐ glycosides) The glycosides that are important in medicine  1. cardiac glycosides all contain steroids as the aglycone. 2. Other glycosides include antibiotics such as streptomycin.
  52. 52. Disaccharides ‐ Disaccharide consists of two sugars joined by an O‐ glycosidic bond. ‐ The most abundant disaccharides are sucrose, lactose and maltose. ‐ Other disaccharides include isomaltose, cellobiose and trehalose. ‐The disaccharides can be classified into homo disaccharides and  hetero disaccharides.  ‐A) Homo disaccharides: are formed of the same monosaccharide units  and include maltose, isomaltose, cellobiose and trehalose. ‐(B) Hetero disaccharides: are formed of different monosaccharide  units and include: sucrose, lactose. 
  53. 53. Lactose:Lactose: It is formed of -galactose and -glucose linked by -1,4-glucosidic linkage Contain free anomeric carbon so reducing sugar It may appear in urine in late pregnancy and during lactation. O OH H H H OHH OH CH2OH H O H OH ..... H H ..... OH H OHH OH CH2OH H and Lactose -Galactose Glucose 1 4O
  54. 54. SucroseSucrose • α D-glucopyranose and β D fructofuranose by α 1- 2 glycosidic bond • No free aldehyde or keton gp so non reducing sugar • hydrolysed to glucose and fructose by sucrase (invertase) enzyme. • * Sucrose is dextrorotatory +66.5. O H OH H H OHH OH CH2OH H 1 Sucrose -Glucose -Fructose CH2OH O H CH2OH OH H H OH O 2
  55. 55. Maltose (malt sugar):Maltose (malt sugar): It consists of 2It consists of 2 --glucose units linked byglucose units linked by --1,41,4--glucosidic linkage,glucosidic linkage, Contain free anomeric carbon so reducing sugar. O H OH H H OHH OH CH 2OH H O H OH ..... H H ..... OH H OHH OH CH 2OH H O and Maltose -Glucose Glucose 1 4
  56. 56. B.B. TrehaloseTrehalose:: It is formed of 2 -glucose units linked by -1,1- glucosidic linkage. Not Contain free anomeric carbon so non reducing sugar Present in a highly toxic lipid extracted from Mycobacterium tuberculosis. O H OH H H OHH OH CH 2O H H O H H OH HO H2C H OHH OH H O 11 Trehalose  -Glucose  -Glucose
  57. 57. Disaccharides Components Reduction 1- sucrose = cane sugar = beet sugar = table sugar α D- glucopyranose and β D fructofuranose. by α 1- 2 glycosidic bond No free aldehyde or keton gp so non reducing sugar hydrolysed to glucose and fructose by sucrase (invertase) enzyme. * Sucrose is dextrorotatory +66.5. 2- Lactose (milk sugar) β D galactose and α D glucose. by β 1-4 glycosidic bond Contain free anomeric carbon so reducing sugar * It may appear in urine in late pregnancy and during lactation.
  58. 58. Disaccharides *Components Bond Reduction 1- Maltose 2αD-glucose α 1-4 glycosidic Contain free anomeric carbon so reducing sugar. 4- Trehalose 2αD-glucose α 1-1 glycosidic Not Contain free anomeric carbon so non reducing sugar
  59. 59. Oligosaccharides • Oligosaccharides contain from 3 to 10 monosaccharide units. • Raffinose An oligosaccharide found in peas and beans
  60. 60. Polysaccharides (glycans) ‐ Polysaccharides consist of more than 10 monosaccharide units and /  or their derivatives Classification According to structure: 1‐ Homo polysaccharides (Homo glycans): contain only one type of  monosaccharide molecule. E.g. starch, glycogen,  dextrin, cellulose, inulin and chitin 2‐ Hetero polysaccharides: contain more than one type of  monosaccharides.  E.g. glycosaminoglycan, glycoprotein.
  61. 61. 1. Starch ‐ is a homopolymer of glucose forming an α‐ glucosidic chain, called a  glucosan or glucan.  ‐It is the most abundant dietary carbohydrate in cereals, potatoes,  legumes, and other vegetables.  ‐The two main constituents are amylose (15–20%), which has a  nonbranching helical structure) and amylopectin (80–85%), which consists of branched chains composed of 24–30  glucose residues united by 1 → 4linkages in the chains and by 1 → 6  linkages at the branch points. :Dextrins2.  Are intermediates in the hydrolysis of starch.
  62. 62. •• AmyloseAmylose::.. Straight chain compoundStraight chain compound present in the form glucose unitspresent in the form glucose units linked bylinked by --1,41,4--glucosidic bond of aglucosidic bond of a helix formed of a large number ofhelix formed of a large number of -- glucose.glucose. O H H H OHH OH CH 2 OH H O H H OHH OH CH 2 OH H O Am ylose 14 n O O 1 4 It forms the inner part of starch granules
  63. 63. :Glycogen3.  ‐ is the storage polysaccharide in animals. ‐ It is a more highly branched structure than amylopectin, with chains  of 12–14 α‐D‐glucopyranose residues in α[1 → 4]‐glucosidic linkage), with branching by means of α(1 → 6)‐glucosidic bonds :Inulin4.   is a polysaccharide of FRUCTOSE (and hence a fructosan) found in plants. It is readily soluble in water . is used to determine the glomerular filtration rate.
  64. 64. Cellulose 5.  ‐Is the chief constituent of the framework of plants.  ‐It is insoluble ‐consists of β‐D‐glucopyranose units linked by β(1 → 4) bonds to form  long, straight chains strengthened by cross‐linked hydrogen bonds.  Cellulose cannot be digested by mammals because of the absence of an enzyme that hydrolyzes the β linkage. It is an important source of “bulk” in the diet. So prevent constipation. ‐ Starch Cellulose
  65. 65. 6. Chitin  is a structural polysaccharide in the exoskeleton of crustaceans and insects and also in mushrooms.  It consists of N‐acetyl‐D‐glucosamine units joined by β (1 →4)‐glycosidic linkages
  66. 66. Glycosaminoglycans (GAGs) (Mucopolysaccharides) ‐ Glycosaminoglycans are long linear (unbranched)  heteropolysaccharide chains generally composed of a repeating  disaccharide unit (acidic sugar‐amino sugar)n.  ‐The  amino  sugar  is  either  D‐glucosamine or  D‐galactosamine in  which  the  amino  group  is  usually  acetylated,  and  sometimes  sulphated. There are 6 types:  1. heparin.              2. heparan sulphate.        3. dermatan sulphate 4. keratan s            5. Chondroitin s                 6. hyaluronic acid
  67. 67. )mucopolysaccharides(Glycosaminoglycans All of the glycosaminoglycans except hyaluronic acid and heparin are  found covalently attached to protein, forming proteoglycan monomers. Their property of holding large quantities of water and occupying  space lubricating other structures, is due to the large number of OH  groups and negative charges on the molecules, which, by repulsion,  keep the carbohydrate chains apart. 
  68. 68. Glycoproteins ‐Are proteins to which oligosaccharides are covalently attached. ‐ Oligosaccharide chains  formed mainly  of  sialic acids  and L‐fucose. ‐ Sialic acids are N‐ or O‐derivatives of neuraminic acid . ‐ Neuraminic acid is a nine‐carbon sugar derived from mannosamine and pyruvate.
  69. 69. • Glycoproteins have many functions: • 1- Soluble as enzymes, hormones and antibodies. • 2- In lysosomes • 3- attached to the cell membrane (The membrane bound glycoproteins) participate in: – a- cell surface recognition (by other cells, hormones, viruses) – b- Cell surface antigenicity (as blood gp antigens)
  70. 70. Proteoglycans Glycoprotein Carbohydrate components Glycosaminoglycans - Repeating disaccharide unit - Linear (unbranched) - long - Contain uronic acids (glucuronic and iduronic - N- acetyl hexosamine - Contain hexoses as galactose (in keratin sulphate) - contain sulphate - No pentoses - No deoxy sugar Oligosaccharides - No repeating units - Branched - short - contain sialic acid derivatives (NANA) - N- acetyl hexasamine - Contain hexoses as galactose and mannose - No sulphate - Contain pentose -Contain deoxy sugar as L-fucose
  71. 71. 2- Tissue distribution and functions Structural - Cartilage - Bone - Tendons - Cell membrane - Cornea Functional and structural - mucines - Blood groups antigens - some hormones - enzymes - Immunoglobulins and receptors
  72. 72. AcidNeuraminic-Acetyl–NANA=N - Neuraminic Acid=sialic acid = mannosamine + pyruvic acid = amino sugar acid - NANA found in glycoproteins.
  73. 73. Fucose-L galactose-L–deoxy-= 6 =Methyl pentose Found in glycoprotein
  74. 74. THE END! Thank You