Question

Peptidoglycan (mucopeptide) is found in walls of
A. Only gram +ve bacteria
B. Both gram +ve and –ve bacteria
C. Gram +ve, -ve bacteria and fungi
D. Bacteria and green algae

Answer 1

Hint: Peptidoglycan is a polymer of sugar and amino acids. Its synthesis can be targeted by antibiotics. It is not present in humans that is why humans are not killed by antibiotics. It is a major component of their existence.

Complete answer: The term peptidoglycan was derived from the peptides and sugars that make a molecule. Peptidoglycan is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The special amino acids found in this layer are Diaminopimelic acid and D- alanine.
It serves as a structural role in the cell walls of bacteria, giving structural strength and counteracting the osmotic pressure of the cytoplasm.
As biology is incomplete without exceptions, here Archaebacteria and mycoplasma lack the peptidoglycan.
Peptidoglycan forms 90% of the dry weight of gram-positive bacteria but only 10% of the gram-negative bacteria. Thus, peptidoglycan is a distinguishing feature of the gram-positive bacteria.

So the answer is option B: Both gram +ve and –ve bacteria.

Note: The mucopeptide is insoluble. It is also called murein. It is present in almost all the bacterial cell walls. But its percentage is higher in the cell wall of gram-positive bacteria than in the cell walls of the gram-negative bacteria. Gram-positive bacteria have a thick layer of peptidoglycan.
The cell wall of green algae is made up of glycoproteins and polysaccharides such as carrageenan.
The cell wall of fungi is made of N-acetylglucosamine polymer Chitin. Whereas viruses do not have a cell wall.