Which of the disaccharides maltose, cellobiose, lactose, and sucrose has each of the following structural or reaction characteristics

/ Exams & Certification / By
  1. Which of the disaccharides maltose, cellobiose, lactose, and sucrose has each of the following structural or reaction characteristics? There may be more than one correct answer for a given characteristic. a. Two different monosaccharide units are present. b. Hydrolysis produces only monosaccharides. c. Its glycosidic linkage is a “head-to-head” linkage. d. It is not a reducing sugar.
  2. Draw the structural formulas for the products formed when the following disaccharide is hydrolyzed.
  1. Draw the Haworth projection formula for both anomers of D-idose, a monosaccharide whose Fischer projection formula is

The Correct Answer and Explanation is :

Let’s break this down step by step.

2. Disaccharide Characteristics

a. Two different monosaccharide units are present:

  • Maltose: Composed of two glucose units.
  • Cellobiose: Composed of two glucose units (though linked differently from maltose).
  • Lactose: Composed of one glucose and one galactose unit.
  • Sucrose: Composed of one glucose and one fructose unit.
  • Answer: Lactose and sucrose have two different monosaccharide units.

b. Hydrolysis produces only monosaccharides:

  • Maltose: Hydrolysis produces two glucose units.
  • Cellobiose: Hydrolysis produces two glucose units.
  • Lactose: Hydrolysis produces one glucose and one galactose unit.
  • Sucrose: Hydrolysis produces one glucose and one fructose unit.
  • Answer: All disaccharides hydrolyze into monosaccharides.

c. Its glycosidic linkage is a “head-to-head” linkage:

  • Maltose: The glycosidic bond is between the anomeric carbon of one glucose and the hydroxyl group of the second glucose (not a head-to-head linkage).
  • Cellobiose: The glycosidic bond is a β-1,4 linkage, also not head-to-head.
  • Lactose: The glycosidic bond is β-1,4 between glucose and galactose.
  • Sucrose: The glycosidic bond is α-1,2 between glucose and fructose, which is a “head-to-head” linkage.
  • Answer: Sucrose has a head-to-head linkage.

d. It is not a reducing sugar:

  • Maltose: Reducing sugar.
  • Cellobiose: Reducing sugar.
  • Lactose: Reducing sugar.
  • Sucrose: Not a reducing sugar because both anomeric carbons are involved in the glycosidic linkage.
  • Answer: Sucrose is not a reducing sugar.

1. Hydrolysis of a Disaccharide

To visualize the products of hydrolyzing the disaccharide shown in the provided image (which appears to be sucrose), the hydrolysis breaks it into glucose and fructose.

For the hydrolysis of sucrose (C₁₂H₂₂O₁₁), the products would be:

  • Glucose (C₆H₁₂O₆)
  • Fructose (C₆H₁₂O₆)

2. Haworth Projections of D-Idose

The Fischer projection formula for D-idose is given as:

HOCH2-CHOH-CHOH-CHOH-CHOH-CHO

To convert this into the Haworth projection, we first recognize that D-idose is an aldose, so it will form a pyranose ring (6-membered ring) upon cyclization.

  • Alpha-anomer: The hydroxyl group on the anomeric carbon (C1) is on the opposite side of the CH2OH group.
  • Beta-anomer: The hydroxyl group on the anomeric carbon (C1) is on the same side as the CH2OH group.

Now, I will generate the Haworth projection formulas for both anomers of D-idose.

Let me generate the images for you.

Here are the Haworth projection formulas for both anomers of D-idose, showing the alpha and beta configurations. You can see the differences in the positioning of the hydroxyl group at the anomeric carbon. Let me know if you need further explanations or additional images!

Related Posts

Scroll to Top