Peptidoglycan abundance: Approximately what fraction of the dry weight of the cell wall does peptidoglycan account for in many Gram-positive bacteria?

Introduction / Context:
Peptidoglycan is the rigid polymer that gives bacterial cells shape and osmotic protection. Gram-positive bacteria characteristically have thick peptidoglycan layers, whereas Gram-negative bacteria have thinner layers between membranes. Estimating the proportion of peptidoglycan highlights envelope differences relevant to staining and antibiotic action.

Given Data / Assumptions:

• We focus on Gram-positive cell walls, not entire cells.
• Typical values in many Gram-positives are high relative to Gram-negatives.
• The question asks for an approximate fraction by dry weight of the wall.

Concept / Approach:

In Gram-positive bacteria, peptidoglycan can constitute the majority of the cell wall mass, often exceeding 50% of the dry weight and in some species reaching much higher values. This abundance correlates with strong retention of crystal violet during the Gram stain and susceptibility to antibiotics targeting peptidoglycan synthesis (e.g., beta-lactams, glycopeptides).

Step-by-Step Solution:

Verification / Alternative check:

Biochemical analyses of purified walls show high peptidoglycan content along with teichoic acids. In contrast, Gram-negatives have additional outer-membrane constituents such as LPS that reduce the relative peptidoglycan proportion.

Why Other Options Are Wrong:

About 10% or 20% is too low for many Gram-positive walls.

The oddly specific 11% + 0.22% is not a standard value and is inconsistent with typical references.

Common Pitfalls:

Confusing percentage of the whole cell with percentage of the isolated wall; assuming uniformity across all species rather than recognizing typical ranges used in teaching.

Final Answer:

50% or more