Peptidoglycan facts: identify the incorrect statement Which statement about peptidoglycan (murein) is NOT incorrect, i.e., all listed statements are accurate—choose the option that reflects that truth.

Introduction / Context:
Peptidoglycan is the structural hallmark of most bacterial cell walls and a major antibiotic target. Understanding its composition and architecture is essential for grasping Gram staining, osmotic protection, and mechanisms of action of beta-lactams and glycopeptides.

Given Data / Assumptions:

• Peptidoglycan is a carbohydrate-peptide mesh consisting of repeating disaccharide units cross-linked by short peptides.
• It envelopes the cytoplasmic membrane, forming a sacculus that determines cell shape and resists turgor.
• Some bacteria (e.g., Mycoplasma) lack peptidoglycan; however, most bacteria possess it.

Concept / Approach:

Each of the first three statements accurately describes peptidoglycan. Therefore, the correct choice is that none of the statements are incorrect. Option E is false and deliberately misleading; several major pathogens do contain peptidoglycan (e.g., Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli), and only specific groups lack it (e.g., Mycoplasma, certain Chlamydia stages).

Step-by-Step Solution:

Verification / Alternative check:

Standard bacteriology references describe peptidoglycan as a bag-like macromolecule built from glycan strands cross-linked by peptides, supporting the cell envelope.

Why Other Options Are Wrong:

• Options A, B, C: All accurately describe peptidoglycan and thus are not incorrect.
• Option E: Incorrect because many pathogens do have peptidoglycan; it is not 'completely absent' from them.

Common Pitfalls:

• Overgeneralizing exceptions (e.g., Mycoplasma) to all bacteria.
• Confusing LPS (outer membrane of Gram-negative bacteria) with peptidoglycan.

Final Answer:

None of the above