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Chapter 12 Carbohydrates

Chemistry 20. Chapter 12 Carbohydrates. Carbohydrates. Produced by photosynthesis in plants. The major source of energy from our diet. Composed of the elements C, H, and O. C n (H 2 O) n. Photosynthesis. 6CO 2 + 6H 2 O + energy C 6 H 12 O 6 + 6O 2. Respiration. glucose.

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Chapter 12 Carbohydrates

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  1. Chemistry 20 Chapter 12 Carbohydrates

  2. Carbohydrates • Produced by photosynthesis in plants. • The major source of energy from our diet. • Composed of the elements C, H, and O. Cn(H2O)n Photosynthesis 6CO2 + 6H2O + energy C6H12O6 + 6O2 Respiration glucose

  3. Carbohydrates • The most abundant organic compounds in the plant world. • 3/4 of the weight of plants. • 1% of the weight of animals and humans (they do not store). • 65% of the foods in our diet.

  4. Carbohydrates H+ or enzyme 1. Monosaccharide + H2O no hydrolysis H+ or enzyme 2. Disaccharide + H2O two monosaccharide units + H+ or enzyme 3. Polysaccharide + many H2O many monosaccharide units

  5. Monosaccharides A carbohydrate that cannot be split or hydrolyzed into smaller carbohydrates. • Monosaccharides are carbohydrates with: • 3-9 carbon atoms • A carbonyl group (aldehyde or ketone) • Several hydroxyl groups Cn(H2O)n CnH2nOn ║ C ─ H │ H─ C ─ OH │ H─ C ─ OH │ CH2OH O

  6. Monosaccharides - Aldose O ║ C ─ H aldose │ H─ C ─ OH │ H─ C ─ OH │ CH2OH an aldotetrose (Erythose) • Aldose is monosaccharide: • With an aldehyde group and many hydroxyl (-OH) groups. • triose (3C atoms) • tetrose (4C atoms) • pentose (5 C atoms) • hexose (6 C atoms) • “Aldo-” + suffix

  7. Monosaccharides - Ketose CH2OH │ C = O ketose │ H─ C ─ OH │ H─ C ─ OH │ H─ C ─ OH │ CH2OH a ketohexose (Fructose) • Ketose is monosaccharide: • With a ketone group and many hydroxyl (-OH) groups. • triose (3C atoms) • tetrose (4C atoms) • pentose (5 C atoms) • hexose (6 C atoms) • “Keto-” + suffix

  8. Some important Monosaccharides • Glucose • (C6H12O6, aldohexose) – blood sugar • Is found in fruits, vegetables, • corn syrup, and honey. • Is found in disaccharides such as sucrose, lactose, and maltose. • Makes up polysaccharides such as starch, cellulose, and glycogen.

  9. Some important Monosaccharides • Fructose • (C6H12O6, ketohexose), • Is the sweetest of the carbohydrates. • Is found in fruit juices and honey (fruit sugar). • In bloodstream, it is converted to its isomer, glucose. • Is bonded to glucose in sucrose (a disaccharide known as table sugar).

  10. Some important Monosaccharides • Galactose • (C6H12O6, aldohexose), • Has a similar structure to glucose except for the –OH on Carbon 4. • Cannot find in the free form in nature. • Exist in the cellular membranes of the brain and nervous system. • Combines with glucose in lactose (a disaccharide and a sugar in milk).

  11. Disease - Galactosemia Galactosemia missing the enzyme that convert galactose to glucose. Accumulation of galactose in the blood and tissues. Mental retardation and cataract Solution: removing the galactose from food: no milk.

  12. C H O Convert to Fischer Projection C H O H O H H C O H C H O H C H O H 2 2 Fischer Projections • - Horizontal lines represent bonds projecting forward from the stereocenter. • - Vertical lines represent bonds projecting to the rear. • - Only the stereocenter is in the plane. 3D 2D

  13. Fischer Projections 1. Carbon with four different groups bonded to it. 2. The chiral carbon furthest from the carbonyl group (-CHO). H HO L - glucose D - glucose More common in the nature

  14. Amino Sugars • - Amino sugars contain an -NH2 group in place of an -OH group. • - Only three amino sugars are common in nature: • D-glucosamine, D-mannosamine, and D-galactosamine.

  15. Cyclic Structure – Haworth Structure • - Aldehydes and ketones react with alcohols to form hemiacetals. • - Cyclic hemiacetals form readily when the hydroxyl and carbonyl groups • are part of the same molecule.

  16. Cyclic Structure – Haworth Structure 1 1 Anomeric carbon 1 1 1 Alpha (α) Beta () More stable form Anomers

  17. Cyclic Structure – Haworth Structure  1 1  -Glucose-Glucose 1 1 -Galactose-Galactose

  18. CH2OH OH HOCH2 HOCH2 2 2 HO HO H H H OH H CH2OH OH H OH H -fructose-fructose Cyclic Structure – Haworth Structure Anomeric carbon

  19. Cyclic Structure – Haworth Structure  1 1  -Glucose-Glucose Humans have -amylase (an enzyme) and they can digest starch products such as pasta (contain-glucose) Humans do not have β-amylase (an enzyme) and they cannot digest cellulose such as wood or paper (containβ-glucose)

  20. Chair Conformation -D-Glucose (Haworth projection) -D-Glucose (Chair conformation)

  21. -D-glucose Open-chain form α-D-glucose Mutarotation Change in specific rotation that accompanies the equilibration of αand  anomers in aqueous solution. 36% 64% < 0.02%

  22. Physical properties of Monosaccharides • Colorless • Crystalline solids • Soluble in water (H-bond because of OH groups) • Insoluble in nonpolar solvents

  23. Chemical properties of Monosaccharides • Formation of Glycosides (acetals) • Oxidation • Reduction

  24. - Exist almost exclusively in cyclic hemiacetal forms. - They react with an alcohol to give acetals. - Acetals are stable in water and bases but they are hydrolyzed in acids. -D-Glucose Methyl α-D-Glucoside Methyl -D-Glucoside Formation of Glycosides (acetals)

  25. OH Oxidation + Cu2O(s) + 2Cu2+ (Brike red) Benedict’s Reagent (blue) D - glucose D – gluconic acid Oxidation of Monosaccharides Aldonic acids Reducing sugars: reduce another substance.

  26. Oxidation of Monosaccharides O H CH2OH C Rearrangement (Tautomerism) C = O H C OH D-fructose (ketose) D-glucose (aldose)

  27. Enzyme D-glucuronic acid (a uronic acid) D-glucose Oxidation of Monosaccharides primary alcohol at C-6 of a hexose is oxidized to uronic acid by an enzyme (catalyst). Exist in connective tissue Detoxifies foreign phenols and alcohols

  28. CH2OH H2 D - glucose D – Sorbitol (D – glucitol) Reduction of Monosaccharides Alditols Transition metals Sugars alcohols: sweetners in many sugar-free (diet drinks & sugarless gum). Problem: diarrhea and cataract

  29. Disaccharides • A disaccharide: • Consists of two monosaccharides linked by a glycosidic bond(when one –OH group reacts with another –OH group). • Glucose + glucose maltose + H2O • Glucose + galactose lactose + H2O • Glucose + fructose sucrose + H2O

  30. Disaccharides • Maltose: • Is a disaccharide of two glucose molecules. • Has a α -1,4-glycosidic bond (between two α-glucoses). • Is obtained from the breakdown of starches. • Is used in cereals and candies. • Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize).  -1,4-glycosidic bond  + 1 1 4 4 α-glucose α-glucose - maltose

  31. Disaccharides • Lactose: • Is a disaccharide of galactose and glucose. • Has a β -1,4-glycosidicbond (between β-galactoseandα-gulcose). • Is found in milk and milk products (almost no sweet). • Is a reducing sugar(carbon 1 can open to give a free aldehyde to oxidize).  -lactose

  32. Disaccharides • Sucrose: • Is found in table sugar (obtained from sugar cane and sugar beets). • Consists of glucose and fructose. • Has an α,β-1,2-glycosidic bond(between α-glucose and -fructose). • Is not a reducing sugar(carbon 1 cannot open to give a free aldehyde • to oxidize).

  33. Polysaccharides • Polymers of many monosaccharides units. • Amylose (20%) • Starch • Amylopectin (80%) • Glycogen(animal starch in muscle and liver. It is • hydrolyzed in our cells and provides energy ). • Cellulose(plant and wood structures). (starch that stores glucose in plants such as rice, potatoes, beans, and wheat - energy storage).

  34. Polysaccharides • Amylose: • Is a polysaccharide of α-glucose in a • continuous (unbranched) chain (helical or coil • form). • Has α-1,4-glycosidic bonds between the • α-glucose units (250 to 4000 units). α-1,4-glycosidic bond

  35. Polysaccharides • Amylopectin: • Is a polysaccharide of glucose units in branched chains. • Has α-1,4-glycosidic bonds between the α-glucose units. • Has α-1,6 bonds to branches of glucose units. • (at about every 25 glucose units, there is a branch). • Glycogen has same structure (more highly branched-every 10-15 units).

  36. Polysaccharides Amlose, Amylopectin (starch) H+ or amylase (enzyme in saliva) Digestion process Dextrins (6-8 glucose units) H+ or amylase (enzyme in saliva) Maltose (2 glucose units) H+ or maltase (enzyme) Many α-D-glucose units

  37. Respiration C6H12O6 + 6O2 6CO2 + 6H2O + energy glucose Fermentation Yeast C6H12O6 2C2H5OH + CO2 + energy Ethanol

  38. Polysaccharides • Cellulose: • Is a polysaccharide of glucose units in unbranched chains with ß-1,4-glycosidic bonds (2200 glucose units). • Has rigid structure (H-bond) and insoluble in water. • Is the major structural material of wood & plants (cotton: 100%). • Cannot be digested by humans because of the • ß-1,4-glycosidic bonds (needs a special enzyme).

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