The cell wall component because of which class cynophyceae has been renamed as cyanobacteria is:

Question

Accepted Answer

The correct option is 4: Murein

The correct option is **Murein** because it is the defining molecular component that necessitated the reclassification of the group formerly known as Cyanophyceae. The term Murein is, in fact, an older synonym for **Peptidoglycan**, which is the rigid, characteristic structural polymer found exclusively in the cell walls of true Bacteria (Eubacteria). Historically, the group was called Cyanophyceae (Blue-green algae) and was classified alongside eukaryotic algae due to their photosynthetic pigment (chlorophyll *a*) and aquatic habitat. However, detailed ultrastructural studies revealed that these organisms lacked a membrane-bound nucleus and other organelles, confirming their prokaryotic cellular organization. The definitive, undeniable proof of their prokaryotic nature—and thus their bacterial identity—was the presence of a cell wall chemically composed of this Murein (Peptidoglycan), compelling taxonomists to rename the group to **Cyanobacteria** to accurately reflect their true phylogeny. This fundamental difference in cell wall chemistry provides a clear, biological distinction from all eukaryotic algae.

The incorrect option is 1: Gelatin

Gelatin is an animal-derived protein product formed from collagen and is not a structural component of the cell wall in any known plant, algae, or bacterium. While Gelatin is used as a solidification agent in certain microbiological media (nutrient agar), it is an external substance and does not contribute to the inherent chemical composition of the Cyanophyceae cell wall. Therefore, the presence or absence of gelatin in the organism's structure or environment has no bearing on its classification as a bacterium or an alga. Gelatin's primary biological role is structural in animal connective tissue, placing it entirely outside the context of microbial cell walls and reclassification debates.

The incorrect option is 2: Pectin

Pectin is a complex polysaccharide that serves as a major structural component in the middle lamella and primary cell walls of terrestrial plants and many groups of eukaryotic algae. Its primary function is to provide strength and act as a cementing agent between adjacent cells. If the cell walls of Cyanophyceae had been found to contain Pectin, this discovery would have actually supported their continued classification as a form of eukaryotic alga. The classification change was driven by the realization that their cell wall was *not* like that of plants or algae, and thus, Pectin is the wrong chemical marker for their bacterial identity.

The incorrect option is 3: Pseudopeptidoglycan

Pseudopeptidoglycan, also known as pseudomurein, is the main cell wall material found in certain species of **Archaea**, a domain of life distinct from Bacteria and Eukarya. Although it structurally and functionally resembles bacterial Peptidoglycan, it differs significantly in its chemical make-up; for instance, it contains $N$-acetyltalosaminuronic acid instead of $N$-acetylmuramic acid and has $\beta$-1,3 glycosidic bonds instead of $\beta$-1,4 bonds. While Cyanobacteria are indeed prokaryotes, they belong to the domain Bacteria, not Archaea. Therefore, the presence of Pseudopeptidoglycan would classify them as Archaea, which is incorrect, confirming that Murein (Peptidoglycan) is the correct defining component.