Question

Which of the following statement is incorrect :

• A. Amylose is water soluble fraction of starch
• B. Amylopectin is water-insoluble fraction of starch
• C. $\alpha$- D Glucose units are present in amylose and amylopectin.
• D. Amylose is water-insoluble fraction of starch

Hint:

To remember starch fractions:
- Amylose = One line (Linear), Soluble (in hot water), $\alpha(1\rightarrow4)$ links only.
- Amylopectin = Packed with branches (Branched), Insoluble, both $\alpha(1\rightarrow4)$ and $\alpha(1\rightarrow6)$ links.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Starch is a major plant storage polysaccharide made up of two distinct polymer fractions: amylose and amylopectin.
Both fractions are composed entirely of D-glucose monomers but differ in their branching patterns, size, and solubility.

Step 3: Detailed Explanation:
Let us analyze each statement to identify the incorrect one:
Statement (A): "Amylose is water soluble fraction of starch"
This statement is correct.
Amylose is a linear polymer of $\alpha$-D-glucose units joined by $\alpha(1\rightarrow4)$ glycosidic bonds.
It makes up about $15 - 20\%$ of starch and is soluble in hot water.
Statement (B): "Amylopectin is water-insoluble fraction of starch"
This statement is correct.
Amylopectin is a highly branched polymer of $\alpha$-D-glucose units.
It contains $\alpha(1\rightarrow4)$ linear linkages and $\alpha(1\rightarrow6)$ branching points.
It makes up about $80 - 85\%$ of starch and is insoluble in water.
Statement (C): "$\alpha$- D Glucose units are present in amylose and amylopectin."
This statement is correct.
Both amylose and amylopectin are homopolysaccharides composed entirely of $\alpha$-D-glucose monomers.
Statement (D): "Amylose is water-insoluble fraction of starch"
This statement is incorrect.
As explained in Statement (A), amylose is the water-soluble fraction of starch, not the water-insoluble fraction.

Step 4: Final Answer:
The incorrect statement is "Amylose is water-insoluble fraction of starch."
Therefore, the correct option is (D).