Question

Which of the following statement options accurately describes the structural carbohydrate linkages present inside a standard molecule of Sucrose?

• A. It contains a standard C-1 to C-4 glycosidic bridge linking two identical \(\alpha\)-D-glucose rings together.
• B. It features a glycosidic linkage connecting the C-1 carbon of an \(\alpha\)-D-glucose unit to the C-2 carbon of a \(\beta\)-D-fructose unit.
• C. It consists of a C-1 to C-4 linkage binding a \(\beta\)-D-galactose ring directly onto a neighboring glucose molecule.
• D. It is formed by a continuous chain of \(\beta\)-D-glucose blocks linked entirely via C-1 to C-6 branch channels.

Hint:

Important disaccharides and their linkages:

• Sucrose \(=\) Glucose + Fructose \(\rightarrow \alpha(1 \rightarrow 2)\beta\)
• Maltose \(=\) Glucose + Glucose \(\rightarrow \alpha(1 \rightarrow 4)\)
• Lactose \(=\) Galactose + Glucose \(\rightarrow \beta(1 \rightarrow 4)\)

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Sucrose is a disaccharide, commonly known as table sugar.
Disaccharides are formed when two monosaccharides are joined by a glycosidic linkage through a condensation (dehydration) reaction.
The structural description of a disaccharide requires identifying the specific monomers and the exact carbon atoms participating in the bond.
A key characteristic of sucrose is that it is a non-reducing sugar, which tells us that the anomeric carbons of both monosaccharides are involved in the bond formation.
Step 2: Detailed Explanation:
1. Monomeric Units: Sucrose is composed of one molecule of \(\alpha\)-D-glucose and one molecule of \(\beta\)-D-fructose.
2. Linkage Specifics:
- In \(\alpha\)-D-glucose, the anomeric carbon is C-1.
- In \(\beta\)-D-fructose, the anomeric carbon is C-2.
- The glycosidic bond connects the C-1 of the glucose unit to the C-2 of the fructose unit.
- Specifically, it is an \(\alpha(1 \rightarrow 2)\beta\) glycosidic linkage.
3. Consequences of the Structure: Because the reactive functional groups (the aldehyde group of glucose and the ketone group of fructose) are sequestered within the glycosidic bond, sucrose cannot undergo mutarotation and does not react with Tollen's or Fehling's reagents.
4. Comparison with Other Options:
- Option (A) describes Maltose, which is two glucose units linked via \(\alpha\)-1,4.
- Option (C) describes Lactose, which is galactose and glucose linked via \(\beta\)-1,4.
- Option (D) describes the branching structure found in polysaccharides like Glycogen or Amylopectin.
Step 3: Final Answer:
The statement in option (B) correctly identifies the monomers (glucose and fructose) and the carbons (C-1 and C-2) involved in the sucrose structure.
Thus, (B) is the correct answer.