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Introduction to carbohydrates


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An introduction to carbohydrates and the types of carbohydrates

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Introduction to carbohydrates

  2. 2. BIOMOLECULES OF LIFE Carbohydrates: Life’s Sweet Molecules
  3. 3. Carbohydrates Carbohydrates are • a major source of energy from our diet. • composed of the elements C, H and O. • also called saccharides, which means “sugars.”
  4. 4. Carbohydrates Carbohydrates • are produced by photosynthesis in plants. • such as glucose are synthesized in plants from CO2, H2O, and energy from the sun. • are oxidized in living cells to produce CO2, H2O, and energy.
  5. 5. • Carbohydrates are sugars and provide energy when consumed. • Our bodies break down carbohydrates to extract energy. Carbon dioxide and water are released in the process. • Glucose is the primary carbohydrate our bodies use to produce energy. • Carbohydrates are classified as biomolecules.
  6. 6. • Simple carbohydrates are referred to as simple sugars and are often sweet to the taste. • Consumption of more sugar than is needed for energy results in conversion of these sugars to fat. • Complex carbohydrates include starches and the plant and wood fibers known as cellulose.
  7. 7. Introduction to Carbohydrates, Continued • Carbohydrates are found on the surface of cells where they act as “road signs” allowing molecules to distinguish one cell from another. • ABO blood markers found on red blood cells are made up of carbohydrates. They allow us to distinguish our body’s blood type from a foreign blood type. • Carbohydrates in our body prevent blood clots. They are also found in our genetic material.
  8. 8. • Carbohydrates also can combine with lipids to form glycolipids OR • With proteins to form glycoproteins.
  9. 9. Examples of isomers: 1. Glucose 2. Fructose 3. Galactose 4. Mannose Same chemical formula C6 H12 O6
  10. 10. EPIMERS • EPIMERS are sugars that differ in configuration at ONLY 1 POSITION.
  11. 11. • Examples of epimers : – D-glucose & D-galactose (epimeric at C4) – D-glucose & D-mannose (epimeric at C2) – D-idose & L-glucose (epimeric at C5)
  12. 12. ENANTIOMERS Non-Superimposable COMPLETE mirror image (differ in configuration at EVERY CHIRAL CENTER.
  13. 13. The two members of the pair are designated as D and L forms. In D form the OH group on the asymmetric carbon is on the right. In L form the OH group is on the left side. D-glucose and L-glucose are enantiomers:
  14. 14. Classes of Carbohydrates • Monosaccharides are the simplest carbohydrates. They cannot be broken down to smaller carbohydrates. • Disaccharides consist of two monosaccharide units joined together; they can be split into two monosaccharides. Sucrose, table sugar, can be broken down into glucose and fructose. • Oligosaccharides contain anywhere from three to nine monosaccharide units. ABO blood groups are oligosaccharides.
  15. 15. 20 Classes of Carbohydrates, Continued Polysaccharides are large molecules containing 10 or more monosaccharide units. Carbohydrate units are connected in one continuous chain or the chain can be branched.
  16. 16. Chapter 5 21 © 2011 Pearson Education, Inc. Monosaccharides, Continued Some Important Monosaccharides • Glucose is the most abundant monosaccharide found in nature. • Glucose is also known as dextrose, blood sugar, and grape sugar. • Glucose is broken down in cells to produce energy.
  17. 17. Monosaccharides, Continued • Diabetics have difficulty getting glucose in their cells, which is why they must monitor their blood glucose levels regularly. • Glucose is one of the monosaccharides of sucrose (table sugar) and lactose (milk sugar) as well as the polysaccharides glycogen, starch, and cellulose.
  18. 18. Monosaccharides, Continued • Galactose is found combined with glucose in the disaccharide lactose, which is present in milk and other dairy products. • A single chiral center (carbon 4) in galactose is arranged opposite that of glucose, which makes it a diastereomer of glucose. • Diastereomers that differ by one chiral center are called epimers.
  19. 19. cyclization • Less then 1%of CHO exist in an open chain form. • Predominantly found in ring form. • involving reaction of C-5 OH group with the C-1 aldehyde group or C-2 of keto group.
  20. 20. • Six membered ring structures are called Pyranoses . • five membered ring structures are called Furanoses .
  21. 21. Monosaccharides, Continued • Mannose, a monosaccharide, is found in some fruits and vegetables. • Cranberries contain high amounts of mannose, which has been shown to be effective in urinary tract infections. • Mannose is an epimer of glucose.
  22. 22. Monosaccharides, Continued • Fructose, a ketose, is commonly referred to as fruit sugar or levulose. • Fructose is combined with glucose to give sucrose, or table sugar. • Fructose is the sweetest monosaccharide and is found in fruits, vegetables, and honey. • Fructose is not an epimer of glucose, but it can be broken down for energy in the body.
  23. 23. Oxidation and Reduction Reactions, Continued Monosaccharides and Redox • An aldehyde functional group can undergo oxidation by gaining oxygen or it can undergo reduction by gaining hydrogen. • During oxidation, aldehydes form carboxylic acids, and during reduction, they form alcohols. • In monosaccharides, oxidation produces a sugar acid, and reduction produces a sugar alcohol.
  24. 24. Oxidation and Reduction Reactions, Continued • Benedict’s test is a useful test to determine the presence of an oxidation reaction that occurs with sugars. • Aldose sugars are oxidized by Cu2+ ion, while the Cu2+ ion is reduced to Cu+ ion.
  25. 25. 33 Oxidation and Reduction Reactions, Continued The product of this reaction, copper(I) oxide (Cu2O), is not soluble and forms a brick red precipitate in solution.
  26. 26. Oxidation and Reduction Reactions, Continued • Aldoses are easily oxidized. They serve as reducing agents and are referred to as reducing sugars. • Fructose and other ketoses are also reducing sugars, even though they do not contain an aldehyde group. • The oxidizing agents can cause a rearrangement of the ketose to an aldose.
  27. 27. Oxidation and Reduction Reactions, Continued • Benedict’s test can be used in urine dipsticks to determine the level of glucose in urine. Excess glucose in urine suggests high levels of glucose in blood, which is an indicator of diabetes. • Aldoses or ketoses can be reduced by hydrogen under the correct conditions, producing sugar alcohols. • Sugar alcohols are produced commercially as artificial sweeteners and found in sugar-free foods.
  28. 28. 36 Oxidation and Reduction Reactions, Continued • When glucose levels are high in the blood stream, sorbitol can be produced by an enzyme called aldose reductase. • High levels of sorbitol can contribute to cataracts, which is a clouding of the lens in the eye. • Cataracts are commonly seen in diabetics.
  29. 29. 37 Disaccharides Condensation and Hydrolysis—Forming and Breaking Glycosidic Bonds • The –OH group that is most reactive in a monosaccharide is the one on the anomeric carbon. • When this hydroxyl group reacts with another hydroxyl group on another monosaccharide a glycosidic bond is formed.
  30. 30. Disaccharides, Continued Formation of glycosides is an example of another type of organic reaction. During this reaction, a molecule of water is eliminated as two molecules join.
  31. 31. Disaccharides, Continued • Condensation reaction is a type of reaction that occurs when two molecules are joined and a water molecule is produced. This type of reaction is referred to as a dehydration reaction. • Hydrolysis reaction is the reverse of a condensation reaction. A larger molecule forms two smaller molecules and water is consumed as a reactant.
  32. 32. Disaccharides, Continued Condensation reactions occur between different types of functional groups that contain an –H in a polar bond, like O–H or N–H, and an –OH group that can be removed to form water.
  33. 33. Disaccharides, Continued • In the case of maltose, the glycosidic bond is specified as α(1→4) and is simply stated as alpha-one-four. • If the –OH group had been in the beta configuration when the glycosidic bond was formed, the bond would be in the β(1→4) configuration. The molecule formed would be named cellobiose and would have a different two-dimensional and three-dimensional shape than maltose.
  34. 34. Chapter 5 42 © 2011 Pearson Education, Inc. Disaccharides, Continued
  35. 35. Chapter 5 43 © 2011 Pearson Education, Inc. Disaccharides, Continued Maltose • Maltose is known as malt sugar. • It is formed by the breakdown of starch. • Malted barley, a key ingredient in beer, contains high levels of maltose. • During germination of barley seeds, the starch goes through hydrolysis to form maltose. This process is halted by drying and roasting barley seeds prior to their germination. • One of the anomeric carbons is free, so maltose is a reducing sugar.
  36. 36. Chapter 5 44 © 2011 Pearson Education, Inc. Disaccharides, Continued Maltose, Continued • The glycosidic bond is α(1→4).
  37. 37. Chapter 5 45 © 2011 Pearson Education, Inc. Disaccharides, Continued Lactose • Lactose is known as milk sugar. • It is found in milk and milk products. • An intolerance to lactose can occur in people who inherit or lose the ability to produce the enzyme lactase that hydrolyzes lactose into its monosaccharide units. • The glycosidic bond is (1→4). • One of the anomeric carbons is free, so lactose is a reducing sugar.
  38. 38. Disaccharides, Continued
  39. 39. Disaccharides, Continued Sucrose • Sucrose is known as table sugar. • It is the most abundant disaccharide found in nature. • Sucrose is found in sugar cane and sugar beets. • The glycosidic bond is  (1→2). • Both anomeric carbons of the monosaccharides in sucrose are bonded, therefore, sucrose is not a reducing sugar. It will not react with Benedict’s reagent.
  40. 40. Disaccharides, Continued
  41. 41. Polysaccharides Polysaccharides Polysaccharides are large molecules of monosaccharides that are connected to each other through their anomeric carbons. There are two types of polysaccharides: 1. Storage polysaccharides contain only  -glucose units. Three important ones are starch, glycogen, and amylopectin. 2. Structural polysaccharides contain only -glucose units. Two important ones are cellulose and chitin. Chitin contains a modified -glucose unit.
  42. 42. Polysaccharides • 2 types: – HOMOpolysaccharides (all 1 type of monomer), e.g., glycogen, starch, cellulose, chitin – HETEROpolysaccharides (different types of monomers), e.g., peptidoglycans, glycosaminoglycans
  43. 43. Chapter 5 51 © 2011 Pearson Education, Inc. Polysaccharides, Continued Storage Polysaccharides Amylose and amylopectin—starch • Starch is a mixture of amylose and amylopectin and is found in plant foods. • Amylose makes up 20% of plant starch and is made up of 250–4000 D-glucose units bonded α(1→4) in a continuous chain. • Long chains of amylose tend to coil. • Amylopectin makes up 80% of plant starch and is made up of D-glucose units connected by α(1→4) glycosidic bonds.
  44. 44. Chapter 5 52 © 2011 Pearson Education, Inc. Polysaccharides, Continued Amylose and amylopectin—starch • About every 25 glucose units of amylopectin, a branch of glucose units are connected to the glucose by an α(1→6) glycosidic bond. • During fruit ripening, starch undergoes hydrolysis of the α(1→4) bonds to produce glucose and maltose, which are sweet. • When we consume starch, our digestive system breaks it down into glucose units for use by our bodies.
  45. 45. Chapter 5 53 © 2011 Pearson Education, Inc. Polysaccharides, Continued
  46. 46. Polysaccharides, Continued Glycogen • Glycogen is a storage polysaccharide found in animals. • Glycogen is stored in the liver and muscles. • Its structure is identical to amylopectin, except that α(1→6) branching occurs about every 12 glucose units. • When glucose is needed, glycogen is hydrolyzed in the liver to glucose.
  47. 47. Glycogen Glycogen • is the polysaccharide that stores α-D-glucose in muscle. • is similar to amylopectin, but is more highly branched.
  48. 48. Polysaccharides, Continued Structural Polysaccharides Cellulose • Cellulose contains glucose units bonded (1→4). • This glycosidic bond configuration changes the three-dimensional shape of cellulose compared with that of amylose. • The chain of glucose units is straight. This allows chains to align next to each other to form a strong rigid structure.
  49. 49. 57 Polysaccharides, Continued
  50. 50. Chapter 5 58 © 2011 Pearson Education, Inc. Carbohydrates and Blood ABO Blood Types • ABO blood types refer to carbohydrates on red blood cells. • These chemical markers are oligosaccharides that contain either three or four sugar units. • Sugar units are D-galactose, L-fucose, N-acetylglucosamine, and N-acetylgalactosamine.
  51. 51. Carbohydrates and Blood, Continued Heparin • Heparin is a medically important polysaccharide because it prevents clotting in the bloodstream. • It is a highly ionic polysaccharide of repeating disaccharide units of an oxidized monosaccharide and D-glucosamine. Heparin also contains sulfate groups that are negatively charged. • It belongs to a group of polysaccharides called glycosaminoglycans.
  52. 52. • Functions: – glucose storage (glycogen in animals & bacteria, starch in plants) – structure (cellulose, chitin, peptidoglycans, glycosaminoglycans – information (cell surface oligo- and polysaccharides, on proteins/glycoproteins and on lipids/glycolipids) • osmotic regulation
  53. 53. • Cellulose and chitin – Function: STRUCTURAL, rigidity important – Cellulose: • homopolymer, b(1-> 4) linked glucose residues • cell walls of plants
  54. 54. – Chitin: • homopolymer, b(1-> 4) linked N- acetylglucosamine residues • hard exoskeletons (shells) of arthropods (e.g., insects, lobsters and crabs)