© 2016 Pearson Education, Inc.General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C.. © 2016 Pearson Education, Inc.General, Organic, and Biological Chemistry: Stru
Trang 1© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Solution
a Ribulose has five carbon atoms (pentose) and is a ketone, which makes it a ketopentose.
b Glucose has six carbon atoms (hexose) and is an aldehyde, which makes it an aldohexose.
Classify each of the following monosaccharides as an aldopentose, ketopentose, aldohexose, or ketohexose:
Sample Problem 15.1 Monosaccharides
Trang 2© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Study Check 15.1
Classify the following monosaccharide, erythrose, as an aldotetrose, ketotetrose, aldopentose, or ketopentose:
Answer
aldotetrose
Sample Problem 15.1 Monosaccharides
Continued
Trang 3© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Solution
Ribulose, which is used in various brands of artificial sweeteners, has the following Fischer projection:
Identify the compound as D- or L-ribulose
Sample Problem 15.2 Fischer Projections for Monosaccharides
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General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Step 1 Number the carbon chain starting at the top of the Fischer projection
Step 2 Locate the chiral carbon farthest from the top of the Fischer projection The chiral carbon farthest from the top is carbon 4
Continued
Sample Problem 15.2 Fischer Projections for Monosaccharides
Trang 5© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Step 3 Identify the position of the —OH group as D- or L- In this Fischer projection, the —OH group is drawn on the right of carbon 4, which makes it D-ribulose
Study Check 15.2
Draw and name the Fischer projection for the mirror image of the ribulose in Sample Problem 15.2
Answer
Continued
Sample Problem 15.2 Fischer Projections for Monosaccharides
Trang 6© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Solution
Step 1 Turn the Fischer projection clockwise by 90°
D-Mannose, a carbohydrate found in immunoglobulins, has the following Fischer projection Draw the Haworth structure for β-d-mannose.
Sample Problem 15.3 Drawing Haworth Structures for Sugars
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General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Step 2 Fold the horizontal carbon chain into a hexagon, rotate the groups on carbon 5, and bond the
O on carbon 5 to carbon 1
Step 3 Draw the new —OH group on carbon 1 above the ring to give the β anomer.
Continued
Sample Problem 15.3 Drawing Haworth Structures for Sugars
Trang 8© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Study Check 15.3
Draw the Haworth structure for α-D-mannose
Answer
Continued
Sample Problem 15.3 Drawing Haworth Structures for Sugars
Trang 9© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Solution
The aldehyde group with an adjacent hydroxyl of D-glucose is easily oxidized by Benedict’s reagent A carbohydrate that reduces Cu2+ to Cu+ is called a reducing sugar
Study Check 15.4
A solution containing a tablet of Benedict’s reagent turns brick red with a urine sample
According to Table 15.1, what might this result indicate?
Why is D-glucose called a reducing sugar?
Sample Problem 15.4 Reducing Sugars
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General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Continued
Sample Problem 15.4 Reducing Sugars
Answer
The brick-red color of the Benedict’s reagent shows a high level of reducing sugar (probably glucose) in the urine, which may indicate type 2 diabetes
Trang 11© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Solution
a. First monosaccharide (left)
Second monosaccharide (right)
b Type of glycosidic bond
c Name of disaccharide
Melibiose is a disaccharide that is 30 times sweeter than sucrose
a. What are the monosaccharide units in melibiose?
b. What type of glycosidic bond links the monosaccharides?
c. Identify the structure as α- or β-melibiose.
Sample Problem 15.5 Glycosidic Bonds in Disaccharides
When the —OH group on carbon 4 is above the plane, it is D-galactose When the —OH group on carbon 1 is below the plane, it is
α-D-galactose
When the —OH group on carbon 4 is below the plane, it is α-D-glucose
The —OH group at carbon 1 of α-D-galactose bonds with the —OH group on carbon 6 of glucose, which makes it an α(1 →
6)-glycosidic bond
The —OH group on carbon 1 of glucose is below the plane, which
α-melibiose.
Trang 12© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Study Check 15.5
Cellobiose is a disaccharide composed of two D-glucose molecules connected by a β(1 → 4)-glycosidic linkage Draw the Haworth structure for β-cellobiose.
Answer
Continued
Sample Problem 15.5 Glycosidic Bonds in Disaccharides
Trang 13© 2016 Pearson Education, Inc.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C Timberlake
Solution
Study Check 15.6
Cellulose and amylose are both unbranched glucose polymers How do they differ?
Answer
Cellulose contains glucose units connected by β(1 → 4)-glycosidic bonds, whereas the glucose units in amylose are connected by α(1 → 4)-glycosidic bonds.
Identify the polysaccharide described by each of the following:
a a polysaccharide that is stored in the liver and muscle tissues
b an unbranched polysaccharide containing β(1 → 4)-glycosidic bonds
c a starch containing α(1 → 4)- and α(1 → 6)-glycosidic bonds
Sample Problem 15.6 tructures of Polysaccharides