Carbohydrate building blocks: β-D-glucose is the repeating monomer in which natural polymer?

Introduction / Context:
Polysaccharides are formed by linking monosaccharides in specific configurations. The stereochemistry (alpha vs beta) of glycosidic bonds dictates structure and properties of the polymer.

Given Data / Assumptions:

• Cellulose consists of β-D-glucose units.
• Starch and glycogen comprise α-D-glucose units.
• Proteins are polymers of amino acids, not sugars.

Concept / Approach:
Cellulose features β(1→4) glycosidic linkages between glucose units, forming linear chains that hydrogen-bond into strong microfibrils. Starch uses α-linkages (amylose: α(1→4), amylopectin: α(1→4) with α(1→6) branches), leading to different digestibility and crystallinity.

Step-by-Step Solution:
Identify the stereochemistry: β-glucose implies cellulose.Exclude α-linked polysaccharides (starch, glycogen).Exclude proteins (amino acid polymers).

Verification / Alternative check:
Cellulose's β-linkages render it indigestible to humans without cellulase enzymes, unlike starch.

Why Other Options Are Wrong:
Starch/glycogen: α-glucose polymers.Protein: peptide backbone, not carbohydrate.

Common Pitfalls:
Confusing α and β linkages; assuming all glucose polymers behave similarly.

Final Answer:
Cellulose