Textbook Question
Oxidation of the aldehyde group of ribose yields a carboxylic acid. Draw the structure of ribonic acid.
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Ch.20 Carbohydrates
McMurry8th EditionFundamentals of GOBISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
Chapter 20, Problem 61
Lactose and maltose are reducing disaccharides, but sucrose is a nonreducing disaccharide. Explain.
Verified step by step guidance1
Understand the concept of reducing and nonreducing sugars: Reducing sugars have a free anomeric carbon (a carbon attached to the carbonyl group in the sugar) that can participate in redox reactions. Nonreducing sugars lack a free anomeric carbon because it is involved in a glycosidic bond.
Examine the structure of lactose: Lactose is composed of glucose and galactose linked by a β(1→4) glycosidic bond. The glucose unit in lactose has a free anomeric carbon, making it a reducing sugar.
Examine the structure of maltose: Maltose is composed of two glucose units linked by an α(1→4) glycosidic bond. One of the glucose units has a free anomeric carbon, making maltose a reducing sugar.
Examine the structure of sucrose: Sucrose is composed of glucose and fructose linked by an α(1→2) glycosidic bond. In this bond, the anomeric carbons of both glucose and fructose are involved, leaving no free anomeric carbon. This makes sucrose a nonreducing sugar.
Conclude: Lactose and maltose are reducing disaccharides because they have a free anomeric carbon capable of participating in redox reactions, while sucrose is a nonreducing disaccharide because both anomeric carbons are involved in the glycosidic bond, preventing redox activity.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reducing Disaccharides
Reducing disaccharides, such as lactose and maltose, contain free aldehyde or ketone groups that can donate electrons to other molecules, thus reducing them. This property allows them to participate in redox reactions, which is a key characteristic in biochemical processes. The presence of a hemiacetal or free anomeric carbon in their structure is what enables this reducing capability.
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Nonreducing Disaccharides
Nonreducing disaccharides, like sucrose, do not have a free aldehyde or ketone group available for reduction. In sucrose, the glycosidic bond forms between the anomeric carbons of glucose and fructose, effectively blocking the potential for oxidation. This structural feature means that sucrose cannot act as a reducing agent in biochemical reactions.
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Glycosidic Bond
A glycosidic bond is a type of covalent bond that links monosaccharides together to form disaccharides and polysaccharides. The formation of this bond involves a condensation reaction, where a water molecule is released. The nature of the glycosidic bond, particularly whether it involves an anomeric carbon, determines whether the resulting disaccharide is reducing or nonreducing.
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Related Practice
Textbook Question
Look at the open-chain form of D-mannose and draw the two glycosidic products that you expect to obtain by reacting D-mannose with methanol.
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Textbook Question
Draw a disaccharide of two cyclic mannose molecules attached by an α-1,4 glycosidic linkage. Explain why the glycosidic products in Problem 20.58 are not reducing sugars, but the product in this problem is a reducing sugar.
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Textbook Question
Amylose (a form of starch) and cellulose are both polymers of glucose. What is the main structural difference between them? What roles do these two polymers have in nature?
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Textbook Question
How are amylose and amylopectin similar to each other, and how are they different from each other?
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Textbook Question
Trehalose, a disaccharide found in the blood of insects, has the following structure. What simple sugars would you obtain on hydrolysis of trehalose? (Hint: Rotate one of the rings in your head or redraw it rotated.)
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