Carbohydrates—Identify the Non-Disaccharide From the list below, select the carbohydrate that is NOT a disaccharide (i.e., it is of a different class such as a polysaccharide).

Difficulty: Easy

Correct Answer: Amylose

Explanation:


Introduction / Context:
Disaccharides are sugars composed of two monosaccharide units (e.g., glucose + glucose for maltose; glucose + galactose for lactose). In contrast, polysaccharides consist of many monosaccharides linked together and serve structural or storage roles. This item asks you to identify the entry that is not a disaccharide.


Given Data / Assumptions:

  • Cellobiose and maltose are glucose-disaccharides (differing in glycosidic linkage).
  • Lactose is a galactose-glucose disaccharide.
  • Amylose is a linear polysaccharide component of starch.


Concept / Approach:
Classify each sugar by its degree of polymerization. Amylose contains long chains of α-1→4-linked glucose units (n ≫ 2), making it a polysaccharide, not a disaccharide. The others listed are classical disaccharides used in laboratory and nutritional contexts.


Step-by-Step Solution:

Recognize cellobiose (β-1→4 glucose-glucose), lactose (β-1→4 galactose-glucose), maltose (α-1→4 glucose-glucose) as disaccharides.Recall amylose as the linear fraction of starch (polysaccharide), not a di-unit sugar.Select amylose as the non-disaccharide.


Verification / Alternative check:
Chemical assays and enzymatic digestion patterns (e.g., amylase on starch) corroborate amylose’s polymeric nature beyond two units.


Why Other Options Are Wrong:

  • Cellobiose, lactose, maltose: each consists of exactly two monosaccharides.
  • “None of these”: incorrect because amylose is demonstrably not a disaccharide.


Common Pitfalls:
Confusing amylose with “amylose unit” or with maltose due to similar names; they differ fundamentally in size and structure.


Final Answer:
Amylose

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