General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.1 Chapter 15 Carbohydrates 15.2 Fischer Projections of Monosaccharides

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.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

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.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 D for the D -isomer

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.4 Examples of D and L Isomers of Monosaccharides

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.5 Learning Check Identify each as the D or L isomer. A.B. C. __-Ribose __-Threose __-Fructose

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.6 Solution Identify each as the D or L isomer. A. B. C. L -Ribose L -Threose D -Fructose

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.7 D -Glucose D -Glucose is  found in fruits, corn syrup, and honey  an aldohexose with the formula C 6 H 12 O 6  known as blood sugar in the body  the monosaccharide in polymers of starch, cellulose, and glycogen

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.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

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.9 D -Fructose  is a ketohexose with the formula C 6 H 12 O 6  is the sweetest carbohydrate  is found in fruit juices and honey  is converted to glucose in the body

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.10 D -Galactose D -Galactose is  an aldohexose with the formula C 6 H 12 O 6  not found free in nature  obtained from lactose, a disaccharide  a similar structure to glucose except for the —OH on C4

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.11 Learning Check Draw the Fischer projection of D -fructose.

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.12 Solution Draw the Fischer projection of D -fructose.