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Chapter 15 Carbohydrates

Chapter 15 Carbohydrates. 15.2 Fischer Projections of Monosaccharides. Fischer Projections. A Fischer projection is used to represent carbohydrates places the most oxidized group at the top shows chiral carbons as the intersection of vertical and horizontal lines. D and L Notations.

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Chapter 15 Carbohydrates

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  1. Chapter 15 Carbohydrates 15.2Fischer Projectionsof Monosaccharides

  2. Fischer Projections A Fischer projection • is used to represent carbohydrates • places the most oxidized group at the top • shows chiral carbons as the intersection of vertical and horizontal lines

  3. D and L Notations In a Fischer projection, the —OH group on the • chiral carbon farthest from the carbonyl group determines an L or D isomer • left is assigned the letter L for the L-isomer • right is assigned the letter Dfor the D-isomer

  4. Examples of D and L Isomers of Monosaccharides

  5. Learning Check Identify each as the D or L isomer. A. B. C. __-Ribose __-Threose __-Fructose

  6. Solution Identify each as the D or L isomer. A. B. C. L-Ribose L-Threose D-Fructose

  7. D-Glucose D-Glucose is • found in fruits, corn syrup, and honey • an aldohexose with the formula C6H12O6 • known as blood sugar in the body • the monosaccharide in polymers of starch, cellulose, and glycogen

  8. Blood Glucose Level In the human body, • glucose has a normal blood level of 70–90 mg/dL • a glucose tolerance test measures blood glucose for several hours after ingesting glucose

  9. D-Fructose D-Fructose • is a ketohexose with the formula C6H12O6 • is the sweetest carbohydrate • is found in fruit juices and honey • is converted to glucose in the body

  10. D-Galactose D-Galactoseis • an aldohexose with the formula C6H12O6 • not found free in nature • obtained from lactose, a disaccharide • a similar structure to glucose except for the —OH on C4

  11. Learning Check Draw the Fischer projection of D-fructose.

  12. Solution Draw the Fischer projection of D-fructose.

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