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Chapter 12 Carbohydrates

Chapter 12 Carbohydrates. Carbohydrates. Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone , or a substance that gives these compounds on hydrolysis. Monosaccharide : a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.

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Chapter 12 Carbohydrates

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  1. Chapter 12 Carbohydrates

  2. Carbohydrates • Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis. • Monosaccharide:a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate. • Monosaccharides have the general formula CnH2nOn, where n varies from 3 to 8. • Aldose: a monosaccharide containing an aldehyde group. • Ketose: a monosaccharide containing a ketone group.

  3. Monosaccharides • Monosaccharides are classified by their number of carbon atoms.

  4. Example: aldo (from aldehyde) pent (from 5 carbons) ose (family name) ALDOPENTOSE

  5. Example • keto (from ketone) • hex (from 6 carbons) • ose (family name) KETOHEXOSE

  6. CHIRALITY

  7. Chiral- compounds or objects that can not be superimposed on their mirror image. Object is different from its mirror image • Achiral (nonchiral)- compounds or objects that can be superimposed on their mirror image. Object is the same as its mirror image

  8. CHIRAL MOLECULES

  9. A chiral carbon is one that has four different groups attached to it. • A carbon with four different groups bonded to it is called a stereocenter.

  10. EXAMPLES

  11. Enantiomers- Isomers where the • molecule and its mirror image are different. • They always occur in pairs

  12. Two Stereocenters • For a molecule with nstereocenters, the maximum number of possible stereoisomers is 2n. • We have already verified that, for a molecule with one stereocenter, 21 = 2 stereoisomers (one pair of enantiomers) are possible. • For a molecule with two stereocenters, a maximum of 22 = 4 stereoisomers (two pair of enantiomers) are possible. • For a molecule with three stereocenters, a maximum of 23 = 8 stereoisomers (four pairs of enantiomers) are possible.

  13. Stereoisomers • example: Mark all stereocenters in each molecule and tell how many stereoisomers are possible for each.

  14. Chirality in Biomolecules • how an enzyme distinguishes between a molecule and its enantiomer.

  15. The S enantiomer of naproxen is the active pain reliever, but its Renantiomer is a liver toxin!

  16. Carvone * *

  17. Thalidomide * *

  18. Fructose

  19. Monosaccharides • Fischer projection:a two dimensional representation for showing the configuration of tetrahedral stereocenters. • Horizontal lines represent bonds projecting forward from the stereocenter. • Vertical lines represent bonds projecting to the rear. • Only the stereocenter is in the plane.

  20. Fischer Projections

  21. D-Glucose forms these cyclic hemiacetals.

  22. Haworth Projections Monosaccharides with 5 or more carbons exist as rings → → Haworth projection ALDOSE

  23. → → Haworth projection Fischer projection KETOSE

  24. Important Monosaccharides • Glucose • Aldohexose • Most nutritionally important monosaccharide • Sometimes called dextrose or blood sugar

  25. Galactose • A component of lactose (milk sugar) • Aldohexose

  26. Fructose • Ketohexose • Sometimes called fruit sugar • Component of sucrose

  27. Disaccharides • Two monosaccharide units linked together Glycosidic Linkage (1→4) Glucose Glucose Maltose

  28. Important Disaccharides • Maltose • Glucose + Glucose • Malt sugar • Found in fermenting grains

  29. Lactose • Glucose + Galactose • Milk sugar

  30. Lactose Intolerance • Enzyme Lactase low or absent • Lactose fermented in the intestine • Nausea, cramps, bloating, gas, and diarrhea

  31. Sucrose • Fructose + Glucose (1→2) • Found in many plants (especially sugar cane, sugar beets) • Table sugar glucose fructose

  32. Polysaccharides • More than 10 monosaccharides linked together Glycosidic linkage

  33. Starch • Polymer of 30 to 1000 glucose units • Storage form of glucose in plants • Cereal grains (wheat, rice, corn, oats, barley) as well as tubers such as potatoes are rich in starch

  34. Glycogen • Polymer of glucose units • Storage form of glucose in animals • Can have up to 600,000 glucose units • Mainly in liver and muscles • (1→4 and 1→6 links)

  35. Cellulose • Polymer of glucose units • Found in plant cell walls • Linear polymer but has  (14)glycosidic linkages. • Not easily digested, a constituent of dietary fiber.

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