5.6. carbohydrate


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5.6. carbohydrate

  1. 1. Carbohydrates
  2. 2. CARBOHYDRATES  polyhydroxy aldehydes and ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones. Most abundant class of biological molecules on Earth  Originally produced through CO fixation during 2 photosynthesis  Empirical formula = (CH O) 2 n 
  3. 3. ROLES OF CARBOHYDRATES Energy storage (glycogen,starch)  Structural components (cellulose,chitin)  Cellular recognition  Carbohydrate derivatives include DNA, RNA, cofactors, glycoproteins, glycolipids 
  4. 4. CARBOHYDRATES CLASSIFICATION    Monosaccharides (simple sugars) cannot be broken down into simpler sugars under mild conditions Oligosaccharides = "a few" - usually 2 to 10 monosaccharides. It is further divided into disaccharides or trisaccharides. Polysaccharides are polymers of the simple sugars with high molecular weight. It is of two types, Homopolysaccharides and heteropolysaccharides
  5. 5. CLASSIFICATION OF MONOSACCHARIDES  (1) (2) Monosaccharides are classified according to: The number of carbon atoms present in the molecules. whether they contain an aldehyde or keto group. Monosaccharides Aldoses (-HC=O) Ketoses (-C=O) Trioses (C3H6O3) Dihydroxyacetone Glyceraldehyde Tetroses (C4H8O4) Erythrose Erythrulose Pentoses (C5H10O5) Ribose Ribulose Hexoses (C6H12O6) Glucose Fructose
  6. 6. MONOSACCHARIDES O H C CH2OH H C* OH HO C* H H C* OH CH2OH D-ribose C O HO C* H H C* OH CH2OH D-ribulose
  7. 7. MONOSACCHARIDES ARE CHIRAL Aldoses with 3C or more and ketoses with 4C or more are chiral  The number of chiral carbons present in a ketose is always one less than the number found in the same length aldose  Number of possible steroisomers = 2n (n = the number of chiral carbons)  O H C CH2OH H C* OH HO C* H H C* H C* C O HO C* H OH H C* OH OH H C* OH CH2OH CH2OH D-glucose D-fructose
  8. 8. STEREOCHEMISTRY Enantiomers O H O C O H C HO C* H H C* OH HO C* HO C* Epimers Diastereomers O H C C C* OH HO C* H H C* OH HO C* H HO C* H HO C* H H C* OH H C* OH HO H H C* OH H C* OH H CH2OH L-glucose D-glucose O H C H CH2OH O H H C H C* OH HO C* H H HO C* H HO C* H C* H H C* OH H C* OH C* OH H C* OH H C* OH CH2OH CH2OH D-mannose D-galactose CH2OH D-glucose •Enantiomers = mirror images •Pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images are diastereomers •Epimers = Two sugars that differ in configuration at only one chiral center CH2OH D-mannose
  9. 9. D VS L DESIGNATION D & L designations are based on the configuration about the single asymmetric C in glyceraldehyde. The lower representations are Fischer Projections. CHO CHO H C OH HO L-glyceraldehyde CHO H C OH CH2OH D-glyceraldehyde H CH2OH CH2OH D-glyceraldehyde C CHO HO C H CH2OH L-glyceraldehyde
  10. 10. SUGAR NOMENCLATURE For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group. Most naturally occurring sugars are D isomers. O H C H – C – OH HO – C – H H – C – OH H – C – OH CH2OH D-glucose O H C HO – C – H H – C – OH HO – C – H HO – C – H CH2OH L-glucose
  11. 11. KETOSES INTRODUCES ADDITIONAL CHIRAL CENTER Aldose sugars (glucose) can cyclize to form a cyclic hemiacetal H H  An aldehyde can react NEW CHIRAL ALDEHYDE O O CARBON with an alcohol to form C H C* R H R O a hemiacetal. R  1 1 ALCOHOL 2 O H R2 HEMIACETAL Ketose sugars (fructose) can cyclize to form a cyclic hemiketal H H  A ketone can react with KETONE O O C R C* R an alcohol to form R R O a hemiketal R  NEW CHIRAL CARBON 1 1 ALCOHOL 2 O H R2 HEMIKETAL
  12. 12. Pentoses and hexoses can cyclize as the ketone or aldehyde reacts with a distal OH. Glucose forms an intra-molecular hemiacetal, as the C1 aldehyde & C5 OH react, to form a 6-member pyranose ring, named after pyran. 1 H HO H H 2 3 4 5 6 CHO C OH C H C OH (linear form) C OH D-glucose CH2OH 6 CH2OH 6 CH2OH 5 H 4 OH O H OH 3 H H H 1 2 OH α-D-glucose OH 5 H 4 OH O H OH 3 H OH H 1 2 OH β-D-glucose These representations of the cyclic sugars are called Haworth projections. H
  13. 13. HAWORTH PROJECTIONS O H C1 H C2 OH HO C3 H H C4 OH H C5 -OH up = beta -OH down = alpha OH CH2OH 6 5 4 1 3 2 Anomeric carbon (most oxidized) For all non-anomeric carbons, -OH groups point down in Haworth projections if pointing right in Fischer projections
  14. 14. Fructose forms either  a 6-member pyranose ring, by reaction of the C2 keto group with the OH on C6, or  a 5-member furanose ring, by reaction of the C2 keto group with the OH on C5.
  15. 15. MONOSACCHARIDES CAN CYCLIZE TO FORM PYRANOSE / FURANOSE FORMS α = 64% β = 36% α = 21.5% β = 58.5% α = 13.5% β = 6.5%
  16. 16. REDUCING SUGARS When in the uncyclized form, monosaccharides act as reducing agents.  Free carbonyl group from aldoses or ketoses can reduce Cu2+ and Ag+ ions to insoluble products 
  19. 19. CHO COOH H C OH HO C H OH H C OH OH H C OH H C OH HO C H H C H C CH2OH D-gluconic acid COOH D-glucuronic acid sugar acid - the aldehyde at C1, or OH at C6, is oxidized to a carboxylic acid; e.g., gluconic acid, glucuronic acid.
  20. 20. SUGAR DERIVATIVES CH2OH CH2OH H O H OH H H OH OH H H NH2 α-D-glucosamine O H OH H H O OH OH H N C CH3 H α-D-N-acetylglucosamine amino sugar - an amino group substitutes for a hydroxyl. An example is glucosamine. The amino group may be acetylated, as in N-acetylglucosamine.
  21. 21. AMINO SUGARS
  22. 22. MONOSACCHARIDE STRUCTURES YOU NEED TO KNOW      Glucose Fructose Ribulose Glyceraldehyde Dihydroxyacetone
  23. 23. GLYCOSIDIC BONDS The anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, splitting out water to form a glycosidic bond: R-OH + HO-R'  R-O-R' + H2O
  24. 24. GLYCOSID IC LINKAGE CH2OH CH2OH hemiacetal O O OH OH OH OH OH OH alcohol OH Hydrolysis H2O H2O Condensation CH2OH O CH2OH acetal OH O OH OH O OH OH OH glycosidic linkage OH
  25. 25. DIASACCHARIDES 6 CH2OH 6 CH2OH 5 H O H OH 4 OH 3 H H 2 OH H H 1 4 5 H OH O maltose O 3 H (α-D-glucosyl-(1->4)-α-D-glucopyranose) H 1 H 2 OH OH
  26. 26. DIASACCHARIDES 6 CH2OH 5 H O H OH 4 OH 3 H  6 CH2OH H 2 OH 5 H O 1 4 H cellobiose O H OH H 2 3 H OH (β-D-glucosyl-(1->4)-β-D-glucopyranose) OH 1 H
  27. 27. DISACCHARIDES sucrose lactose CH2OH CH2OH H O H OH CH2OH H OH O CH2OH O H OH CH2OH H OH O OH H H H H OH H (α-D-glucosyl-(1->2)-β-D-fructofuranose) H O H H O OH OH OH OH H H (β-D-galactosyl-(1->4)-β-Dglucopyranose) OH
  28. 28. POLYSACCHARIDES(GLYCANS):  Linear or Branched polymers STARCH(Glucosan or Glucan)  Plants store glucose as amylose or amylopectin, glucose polymers collectively called starch.  CH2OH H O H OH H 1 OH H OH H H O 6CH OH 2 5 O H 4 OH H 3 H 1 H H O O H OH CH2OH CH2OH CH2OH H H H O O H OH H 2 OH H OH amylose H OH H H O O H OH H H OH H OH
  29. 29. Polysaccharides: Glucose storage in polymeric form minimizes osmotic effects. Amylose is a glucose polymer with α(1→4) linkages. The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end.
  30. 30. CH2OH CH2OH O H H OH H H H CH2OH H OH H H OH H H OH CH2OH O H OH O OH O OH H H OH H H O O H OH H H OH H H O 4 amylopectin H 1 O 6 CH2 5 H OH 3 H CH2OH O H 2 OH H H 1 O CH2OH O H 4 OH H H OH H H O O H OH H H OH H OH Amylopectin is a glucose polymer with mainly α(1→4) linkages, but it also has branches formed by α(1→6) linkages. Branches are generally longer than shown above. The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur.
  31. 31. CH2OH H CH2OH O H OH H H H CH2OH H OH H H OH H H OH CH2OH O H OH O OH O OH H H OH H H O O H OH H H OH H H O 4 glycogen H 1 O 6 CH2 5 H OH 3 H CH2OH O H 2 OH H H 1 O CH2OH O H 4 OH H H OH H H O O H OH H H OH H OH Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin. But glycogen has more α(1→6) branches. The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise. The ability to rapidly mobilize glucose is more essential to animals than to plants.
  32. 32. CH2OH O H H OH H OH H 1 O H H OH 6CH OH 2 5 O H 4 OH 3 H H H 1 2 OH O O H OH CH2OH CH2OH CH2OH H H O O H OH H OH cellulose O H O H OH H OH OH H H H H H H H OH Cellulose, a major constituent of plant cell walls, consists of long linear chains of glucose with β(1→4) linkages. Every other glucose is flipped over, due to β linkages.
  33. 33. CH2OH H O H OH H OH H 1 O H H OH 6CH OH 2 5 O H 4 OH 3 H H H 1 2 OH O O H OH CH2OH CH2OH CH2OH H H O O H OH H OH cellulose O H O H OH H OH OH H H H H H H H OH Multisubunit Cellulose Synthase complexes in the plasma membrane spin out from the cell surface microfibrils consisting of 36 parallel, interacting cellulose chains. These microfibrils are very strong. The role of cellulose is to impart strength and rigidity to plant cell walls, which can withstand high hydrostatic pressure gradients. Osmotic swelling is prevented. Explore and compare structures of amylose & cellulose using Chime.
  34. 34. CH2OH D-glucuronate 6COO H 4 6 H − 5 H OH 3 H 2 OH H 4 O H 5 1 H OH O 3 H O H 2 1 O H NHCOCH3 N-acetyl-D-glucosamine hyaluronate Glycosaminoglycans (mucopolysaccharides) are linear polymers of repeating disaccharides. The constituent monosaccharides tend to be modified, with acidic groups, amino groups, sulfated hydroxyl and amino groups, etc. Glycosaminoglycans tend to be negatively charged, because of the prevalence of acidic groups.
  35. 35. CH2OH D-glucuronate 6 H − 6COO H 4 5 H OH 3 H 2 OH H 4 O H 5 1 H OH O 3 H O H 2 1 O H NHCOCH3 N-acetyl-D-glucosamine hyaluronate Hyaluronate (hyaluronan) is a glycosaminoglycan with a repeating disaccharide consisting of 2 glucose derivatives, glucuronate (glucuronic acid) & N-acetylglucosamine. The glycosidic linkages are β(1→3) & β(1→4).
  36. 36. N-sulfo-glucosamine-6-sulfate iduronate-2-sulfate CH2OSO3− H H COO− OH O H O H O H OH H H H H OSO3− O H NHSO3− heparin or heparan sulfate - examples of residues Heparan sulfate is initially synthesized on a membrane-embedded core protein as a polymer of alternating N-acetylglucosamine and glucuronate residues. Later, in segments of the polymer, glucuronate residues may be converted to the sulfated sugar iduronic acid, while N-acetylglucosamine residues may be deacetylated and/or sulfated.
  37. 37. PDB 1RID Heparin, a soluble glycosaminoglycan found in granules of mast cells, has a structure similar to that of heparan sulfates, but is more highly sulfated. When released into the blood, it inhibits clot formation by interacting with the protein antithrombin. Heparin has an extended helical conformation. heparin: (IDS-SGN)5 C  O  N  S Heparin shown has 10 residues, alternating IDS (iduronate-2-sulfate) & SGN (N-sulfo-glucosamine-6sulfate).
  38. 38. Oligosaccharides that are covalently attached to proteins or to membrane lipids may be linear or branched chains. O-linked oligosaccharide chains of glycoproteins vary in complexity. They link to a protein via a glycosidic bond between a sugar residue & a serine or threonine OH.  O-linked oligosaccharides have roles in recognition, interaction, and enzyme regulation.
  39. 39. CH2OH H O O H OH HN C HN CH2 C H H OH H HN C CH3 O N-acetylglucosamine Initial sugar in N-linked glycoprotein oligosaccharide Asn CH O HN HC R C X O HN HC R C Ser or Thr O N-linked oligosaccharides of glycoproteins tend to be complex and branched. First N-acetylglucosamine is linked to a protein via the side-chain N of an asparagine residue in a particular 3-amino acid sequence.
  40. 40. MULTIPLE CHOICE QUESTION          1. Ribose is differ from Deoxyribose in A. C1 B. C2 C. C3 D. C4 2. All are aldose except A. Glucose B. Galactose C. Mannose D. Fructose 3. The glycosaminoglycan that serves as anticoagulant A. Heparin B. Hyaluronic acid C. Chondroitin Sulfate D. Keratin sulfate 4. Which polysaccharide is composed of b-Glycosidic bonds A. Amylose B. Amylopectin C. Cellulose D. Glycogen 5. Number of asymmetric carbon atom in glucose is: A. One B. Two C. Three D. Four
  41. 41. MULTIPLE CHOICE QUESTION  6. A homopolysaccharide made up of fructose is: A. Glycogen B. Starch C. Cellulose D. Inulin  7. Cyclization of the open chain form of glucose produces A. Hemiacetal B. Anhydride C. Lactone D. Aldehyde  8.Which of the following is an example of a storage polysaccharide made by animals? A. Cellulose B. Glycogen C. Collagen D. Starch.  9. Cellulose, a b(1->4)-linked glucose polysaccharide, differs from starch in that starch is a  A. b(1->6)-linked manose polysaccharide B. b(1->6)-linked glucose polysaccharide. C. an a(1->6)-linked glucose polysaccharide. D. an a(1->4)-linked glucose polysaccharide. E. an a(1->4)-linked mannose polysaccharide.