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Carbohydrates

Carbohydrates. Types of Carbohydrates Classification of Monosaccharides D and L Notations from Fischer Projections Structures of Some Important Monosaccharides. Carbohydrates. Carbohydrates are: A major source of energy from our diet. Composed of the elements C, H and O.

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Carbohydrates

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  1. Carbohydrates • Types of Carbohydrates • Classification of Monosaccharides • D and L Notations from Fischer Projections • Structures of Some Important Monosaccharides

  2. 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”. • Produced by photosynthesis in plants.

  3. Photosynthesis and Respiration • Photosynthesis in plants requires CO2, H2O, and energy from the sun and produces carbohydrates, such as glucose [C6H12O6 = C(H2O)6]. • In respiration, glucose is oxidized in living cells to produce CO2, H2O, and energy.

  4. Types of Carbohydrates • Monosaccharides are the simplest carbohydrates. • Disaccharides consist of two monosaccharides. • Polysaccharides contain many monosaccharides.

  5. Most of the names of carbohydrates end in -ose Glucose-What plants make Maltose- used in making beer (disaccharide) Fructose– found in fruit (monosaccharide) Sucrose- Table sugar (disaccharide) Lactose – In milk (disaccharide)

  6. Classification of Monosaccharides • Aldoses are monosaccharides with analdehydegroup and many hydroxyl (-OH) groups. • Ketoses are monosaccharides with a ketonegroup and many hydroxyl (-OH) groups. Aldose Aldose Ketose

  7. Monosaccharides • Monosaccharides are also classified according to the number of carbon atoms. • A triose has three carbons; a tetrose has four carbons; a pentose has five carbons; and a hexose has six carbons. Triose Tetrose Hexose

  8. 2 | 1—C—3 | 4 2 | 3—C—1 | 4 The two simplest sugars Note Numerous Chiral Carbons

  9. Fischer Projection Haworth Projection • a common way of representing the cyclicstructureofmonosaccharides with a simple three-dimensional perspective. • was named after the English chemist SirWalter N. Haworth. a two-dimensionalrepresentation of thethree-dimensionalstructure of organic molecules. usually used to represent the molecular structures of monosaccharides and amino acids. devised byHermann Emil Fischerin 1891.

  10. Fischer Projections • Is used to represent carbohydrates. • Places the most oxidized group at the top. • Uses horizontal lines for bonds that come forward. • Uses vertical lines for bonds that go back.

  11. D and L Notations • By convention, the letter L is assigned to the structure with the —OH on the left. • The letter D is assigned to the structure with —OH on the right.

  12. D and L Monosaccharides • The —OH on the chiral atom farthest from the carbonyl group is used to assign the D or L configuration. • The D form is usually the isomer found in nature.

  13. D-Glucose • Found in fruits, corn syrup, and honey. • An aldohexose with the formula C6H12O6 • Known as blood sugar in the body.

  14. Blood Glucose Level • In the body, glucose has a normal concentration of 80-110 mg/dL. • In a glucose tolerance test, blood glucose is measured for several hours after ingesting glucose.

  15. D-Fructose • Is a ketohexose with formula of C6H12O6. • Is the sweetest carbohydrate. • Is found in fruit, juices and honey. • Converts to glucose in the body.

  16. D-Galactose • Is not found free in nature. • Is obtained from lactose, a disaccharide. • Is important in cellular membranes.

  17. Cyclic Structures • Monosaccharides with 5-6 carbon atoms form cyclic structures • The hydroxyl group on C-5 reacts with the aldehyde group or ketone group

  18. Sugars Prefer To Be Cyclic

  19. Haworth Structure for D-Isomers The cyclic structure of a D-isomer has the final CH2OH group located above the ring.

  20. Numbered carbons C 6' C O 5' C C 4' 1' C C 3' 2'

  21. Haworth Structure for D-Glucose • The new –OH on C1 has two possibilites: down for anomer, up for  anomer • Isomers that differ only in their configuration about the new asymmetric carbon are called anomers, the carbonyl carbon is called anomeric carbon. • α-anomer • β-anomer

  22. Cyclic Haworth Structures • Stable cyclic hemiacetals form when the C=O group and the • -OH are part of the same molecule. • For hexoses, the hydroxyl group on C-5 reacts with the aldehyde group or ketone group. • The cyclic structure of a D-isomer has the last CH2OH group located above the ring.

  23. Formation of Cyclic Glucose • The Haworth structure can be written from the • Fischer Projection. • The –OH group on the left (C3) is drawn up. • The –OH groups on the right (C2, C4) are drawn down.

  24. Haworth Structure for D-Glucose   -D-Glucose -D-Glucose

  25. Glucose Anomers

  26. cis = b trans = a on right = D CONVERTING TO HAWORTH PROJECTIONS D-(+)-glucose -CH2OH up = D D O W N U P 1 6 BOTH ANOMERS OF A D-SUGAR (D-glucose) 2 5 3 4 1 4 3 2 5 6 HAWORTH PROJECTIONS FISCHER PROJECTION

  27. Mutarotation • A small amount of open chain is in equilibrium with the cyclic forms. • The most stable form of glucose is β-D-glucose. -D-glucose D-glucose (open) β-D-glucose (36%) (trace) (64%)

  28. -D-Glucose • In nature, open chain forms are rare. • All 5 forms coexist with the pyranose forms occurring 99% of the time, furanose about 0.5% each and a trace of open chain and are “anomers”and differ in configuration at the new chiral center formed in the cycle

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