Monomer Configuration Differences in Polysaccharides

Steps:

• Cellulose monomer is β-D-glucose; homogalacturonan monomer is α-D-galacturonic acid.
• Both share OH configurations at C2 and C3, but differ at C1 (anomeric carbon) and C4.
• At C1, glucose has β-OH (equatorial in chair form); galacturonic acid has α-OH (axial).
• At C4, glucose has equatorial OH; galacturonic acid (galactose-derived) has axial OH.

Why A is correct:

• Glycosidic bonds form via C1 (α vs. β linkage) and involve C4 (gluco vs. galacto stereochemistry), directly altering OH arrangements at these carbons per standard carbohydrate nomenclature.

Why the others are wrong:

• B: C3 OH is identically configured (equatorial) in both D-glucose and D-galacturonic acid.
• C: C3 OH configuration matches between monomers; no difference.
• D: C1 anomeric OH also differs (β vs. α), not just C4.

Final answer: A