Bacterial cell walls are mainly composed of?

UPPSC-2021

Applied Microbiology & Infection control

Easy

Appeared in: UPPSC-2021

Explanation

The bacterial cell wall is primarily composed of peptidoglycan (also known as murein), a polymer exclusive to bacteria.
Peptidoglycan provides structural rigidity and shape to the bacterial cell, protecting it from osmotic pressure and lysis.
It consists of repeating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by short peptide chains.
The thickness of the peptidoglycan layer is a key feature used to differentiate between Gram-positive (thick layer) and Gram-negative (thin layer) bacteria.

Option B: Lipoproteins are present, especially in Gram-negative bacteria, where they anchor the outer membrane to the peptidoglycan. However, they are not the main structural component responsible for the wall's rigidity.
Option C: Polysaccharides form the bacterial capsule or slime layer, which is external to the cell wall. They are also part of the lipopolysaccharide (LPS) in Gram-negative bacteria but do not provide the primary structural framework like peptidoglycan.
Option D: Triglycerides are lipids used for energy storage and are not structural components of the bacterial cell wall.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Composition of bacterial cell wall as background academic context rather than a clinical decision trigger.
Understanding the composition of the bacterial cell wall is crucial for antibiotic therapy. Many common antibiotics, such as penicillin and cephalosporins (β-lactams), specifically target and inhibit the synthesis of peptidoglycan, leading to bacterial cell death.
The difference in cell wall structure is the basis for the Gram stain, a fundamental diagnostic test in microbiology. The test's outcome (Gram-positive or Gram-negative) guides the initial choice of antibiotics for treating an infection.
What if? - If a bacterium, like Mycoplasma, naturally lacks a cell wall, antibiotics that target peptidoglycan synthesis (e.g., penicillin) will be completely ineffective. In such cases, alternative antibiotics that target other cellular processes, like protein synthesis (e.g., macrolides or tetracyclines), must be used.

How to Approach the Question

First, identify the core question: What is the main building block of a bacterial cell wall?
This is a factual recall question from microbiology. Access your knowledge about bacterial anatomy.
Evaluate each option. Consider the primary function of each molecule in a bacterial cell.
Peptidoglycan is uniquely associated with the bacterial cell wall's structure and strength.
Eliminate the other options by recalling their roles: Lipoproteins are anchors, polysaccharides are for capsules, and triglycerides are for energy storage.
Confirm that peptidoglycan is the most accurate and primary component among the choices.

Concept Tested & Keywords

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E6 Microbiology Essentials Sastry 4e Part 1 pp. 37-39, 36-38

E6 Microbiology Applied AnjuDhir 3e Part 1 p. 62-64