Which of the following bacterial structures is composed of peptidoglycan and is responsible for maintaining cell shape and rigidity?

Question

Accepted Answer

B. Cell wall. ## Bacterial Cell Wall Structure

**Key Point:** The cell wall is the rigid outer layer of bacteria that provides structural support and maintains cell shape. It is composed primarily of peptidoglycan (murein), a polymer of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by short peptide chains.

## Composition and Function

| Structure | Composition | Primary Function |
| --- | --- | --- |
| Cell wall | Peptidoglycan + teichoic acids (Gram+) or lipopolysaccharide (Gram−) | Rigidity, shape maintenance, protection |
| Cell membrane | Phospholipid bilayer | Selective permeability, transport |
| Capsule | Polysaccharide or protein | Virulence, protection from desiccation |
| Pili | Protein | Attachment, conjugation |

**High-Yield:** Peptidoglycan is unique to bacteria and is the target of β-lactam antibiotics (penicillins, cephalosporins), which inhibit cross-linking of peptidoglycan strands by binding penicillin-binding proteins (PBPs).

**Clinical Pearl:** The thickness and composition of the cell wall differ between Gram-positive and Gram-negative bacteria:
- **Gram-positive:** Thick peptidoglycan layer (20–80 nm) with teichoic acids
- **Gram-negative:** Thin peptidoglycan layer (5–10 nm) sandwiched between inner and outer membranes

**Mnemonic:** **CWPF** = Cell Wall, Peptidoglycan, Firmness, Fixation (the cell wall gives bacteria their fixed shape and structural integrity).

Answer

A. Pili

Answer

C. Cell membrane

Answer

D. Capsule

Which of the following bacterial structures is composed of peptidoglycan and is responsible for maintaining cell shape and rigidity?

Explanation

Bacterial Cell Wall Structure

Composition and Function

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Structure	Composition	Primary Function
Cell wall	Peptidoglycan + teichoic acids (Gram+) or lipopolysaccharide (Gram−)	Rigidity, shape maintenance, protection
Cell membrane	Phospholipid bilayer	Selective permeability, transport
Capsule	Polysaccharide or protein	Virulence, protection from desiccation
Pili	Protein	Attachment, conjugation