In most bacteria, the cell wall is primarily composed of which macromolecular structure?

• A. Chitin, a polymer of $N_2$-acetylglucosamine
• B. Cellulose, a polymer of ${\beta }_1$$\to$$4_{\mathrm{}}$-linked glucose
• C. A phospholipid bilayer with cholesterol as the main structural component
• D. Peptidoglycan (murein), a polymer of sugars cross-linked by short peptides

Answer: (D)