Peptidoglycan chemistry: the N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) sugars in bacterial walls are covalently linked by which glycosidic bond?

Introduction / Context:
Peptidoglycan’s strength derives from both its glycosidic linkages and peptide cross-bridges. Knowing the specific bond between NAG and NAM explains the action of lysozyme and certain antibiotics on bacterial cell walls.

Given Data / Assumptions:

• Sugars involved: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
• We must choose the correct glycosidic linkage connecting them in the backbone.

Concept / Approach:
In peptidoglycan, NAG and NAM residues are joined by β-1,4-glycosidic bonds. This linkage is specifically cleaved by lysozyme, which hydrolyzes the β-1,4 bond and compromises wall integrity, leading to osmotic lysis in susceptible bacteria.

Step-by-Step Solution:

Verification / Alternative check:
Biochemistry references consistently depict the NAG–NAM linkage as β-1,4, analogous to cellulose’s β-1,4 (though different monomers) and unlike starch’s α linkages.

Why Other Options Are Wrong:

• α-1,4 / α-1,6: typical for starch/glycogen branches, not peptidoglycan.
• β-1,6: not the canonical linkage in the NAG–NAM backbone.

Common Pitfalls:
Mixing carbohydrate linkages from eukaryotic storage polysaccharides with bacterial wall polysaccharides.

Final Answer:
β- 1,4-glycosidic bond