Question

Arrange the following structural layers of Gram negative bacterial cell from outside towards inside
A. Outer membrane
B. Peptidoglycan
C. Capsule
D. Cytoplasmic membrane
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. A, C, D, B
• C. C, A, B, D
• D. C, D, B, A

Hint:

Gram-negative bacteria are distinguished by their outer membrane, which contains lipid A (endotoxin). This membrane sits above a thin peptidoglycan layer, with both layers enclosed by an optional capsule.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The cell envelope of a Gram-negative bacterium is a complex, multi-layered structure.
Identifying the spatial arrangement of these layers from the external environment to the cytoplasm is fundamental to understanding bacterial physiology, staining characteristics, and pathogenesis.
Detailed Explanation:
Let us trace the layers of a encapsulated Gram-negative bacterial cell starting from the outermost boundary and moving inward:
1. Capsule (C): The outermost glycocalyx layer. It is typically composed of polysaccharides and serves as a protective barrier against phagocytosis and desiccation.
2. Outer membrane (A): Positioned immediately beneath the capsule. It is an asymmetric lipid bilayer containing lipopolysaccharide (LPS) in the outer leaflet, phospholipids in the inner leaflet, and structural proteins like porins.
3. Peptidoglycan layer (B): A thin, single-layered mesh of glycan chains cross-linked by peptides, located within the aqueous periplasmic space beneath the outer membrane.
4. Cytoplasmic membrane (D): The innermost layer, consisting of a symmetric phospholipid bilayer containing transport proteins. It directly encloses the bacterial cytoplasm.
Therefore, the sequence from outside to inside is Capsule (C) $\rightarrow$ Outer membrane (A) $\rightarrow$ Peptidoglycan (B) $\rightarrow$ Cytoplasmic membrane (D).

Step 2: Final Answer:
This sequence corresponds to the order C, A, B, D, which is Option (C).