Question

Mycoplasmas are different from the other prokaryotes by

• A. Presence of chitin in cell walls
• B. Presence of murrain in cell walls
• C. Presence of proteins in cell walls
• D. Absence of cell wall itself

Hint:

Mycoplasmas are prokaryotes that lack a cell wall, which makes them different from other bacteria and allows them to adopt various shapes.

Answer 1

The Correct Option is D

Most prokaryotes are enclosed by a rigid cell wall built from peptidoglycan (murein), which gives them a fixed shape and protects against osmotic stress. Mycoplasmas are unusual among prokaryotes because they lack this cell wall entirely, being bounded only by a cholesterol-containing plasma membrane. This absence of a cell wall is what gives mycoplasmas their pleomorphic (variable) shape and their natural resistance to cell-wall-targeting antibiotics such as penicillin.

Therefore, the correct answer is Absence of cell wall itself.

Answer 2

Another way to confirm this is to think about the practical consequences that follow from each option, and check which consequence actually matches mycoplasma biology.

1. Presence of chitin in cell walls: If this were true, mycoplasmas would have a rigid, fixed shape, but they are instead known for being highly pleomorphic, which argues against a chitin-based wall.
2. Presence of murrain in cell walls: If a peptidoglycan-based wall were present, antibiotics like penicillin that target peptidoglycan synthesis would be effective against mycoplasmas, but mycoplasmas are naturally resistant to these drugs.
3. Presence of proteins in cell walls: This again assumes a cell wall structure exists, which does not match mycoplasma's known resistance to cell-wall-targeting antibiotics or their variable shape.
4. Absence of cell wall itself: This explains both the variable, flexible shape of mycoplasmas and their natural resistance to antibiotics that act on cell wall synthesis, matching known mycoplasma biology.

Since mycoplasmas are pleomorphic and resistant to cell-wall-targeting antibiotics, the underlying reason is the absence of a cell wall altogether.

Therefore, the correct answer is Absence of cell wall itself.