Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

20. Carbohydrates

Disaccharides

GOB Chemistry

20. Carbohydrates

Disaccharides

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3:22 minutes

Problem 61

Textbook Question

Lactose and maltose are reducing disaccharides, but sucrose is a nonreducing disaccharide. Explain.

Verified step by step guidance

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.

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.

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

Carbohydrates are abbreviated using a three-letter abbreviation followed by their glycosidic bond type. For example, maltose and sucrose can be written respectively as

Provide the structure for the O-type blood carbohydrate set given the following abbreviation:

L-Fucα (1→2) Galß(1→4)GlcNAc

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Multiple Choice

Which disaccharide forms a 1,1-glycosidic linkage?

What is the identity of the disaccharide below?

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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

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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Textbook Question

Are the α and β forms of the disaccharide lactose enantiomers of each other? Why or why not?

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Textbook Question

Indicate whether each disaccharide in Problem 13.41 is a reducing sugar or not.

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Textbook Question

Identify the disaccharide that fits each of the following descriptions: