Bacterial cell wall chemistry: Peptidoglycan (murein) is a complex made of which two major types of building blocks?

Introduction / Context:
Peptidoglycan is the hallmark structural polymer of most bacterial cell walls, providing shape and resistance to osmotic lysis. Knowing its chemical composition explains how antibiotics like beta-lactams and glycopeptides work.

Given Data / Assumptions:

• Peptidoglycan contains sugar backbones and peptide cross-bridges.
• Question seeks the two fundamental chemical classes involved.

Concept / Approach:
Peptidoglycan consists of carbohydrate chains of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by short peptides composed of amino acids (often including D-forms). Thus, it is a carbohydrate plus peptide (amino acid) complex—not a full folded protein.

Step-by-Step Solution:
Identify glycans → carbohydrate backbone (NAG–NAM repeats). Identify linkers → short amino acid chains forming cross-bridges. Choose the pair “amino acid and carbohydrate”. Exclude “protein” wording because cross-links are short peptides, not large proteins.

Verification / Alternative check:
Enzymes like transpeptidases create peptide cross-links; lysozyme cleaves the glycosidic bond between NAG and NAM, confirming the glycan-peptide architecture.

Why Other Options Are Wrong:
Options listing “protein” suggest large polypeptides; peptidoglycan uses short peptides; nucleic acids and lipids are unrelated here.

Common Pitfalls:
Equating any peptide with “protein”; overlooking D-amino acids unique to bacterial cell walls.

Final Answer:
Amino acid and carbohydrate.