22) How many molecules of water are released during the polymerization of a 20 monomer-long cellulose molecule?
A) 10
B) 19
C) 20
D) 40
The Correct Answer and Explanation is :
Correct Answer: B) 19
Explanation:
Cellulose is a polysaccharide composed of β-glucose monomers linked together by β-1,4-glycosidic bonds. The polymerization of cellulose occurs through a condensation reaction (dehydration synthesis), where each monomer is joined to another via the removal of a water (H₂O) molecule.
Understanding Polymerization and Water Release:
- Number of Monomers and Bonds:
- A 20-monomer-long cellulose molecule consists of 20 glucose units.
- These monomers must be linked together via glycosidic bonds.
- The number of glycosidic bonds required to connect n monomers in a straight chain is always (n – 1).
- Water Molecule Release Calculation:
- Each glycosidic bond formation results in the release of one water molecule.
- Since a 20-monomer cellulose chain has 19 glycosidic bonds (one less than the number of monomers), it will release 19 water molecules.
Common Misconceptions:
- Some might think 20 monomers release 20 water molecules, but this is incorrect because the first monomer does not require a bond to another glucose unit.
- The answer is not 40, because each linkage releases one water molecule, not two.
- The answer is not 10, because the dehydration process occurs for every linkage, and we have 19 linkages.
Thus, the correct answer is B) 19, as 19 water molecules are released when 20 glucose monomers polymerize to form cellulose.