Q.18 The lipopolysaccharides present in bacterial cell wall has lipid A which is connected to
- (A) O-polysaccharide
- (B) core polysaccharide
- (C) both with O-polysaccharide and core polysaccharide
- (D) rhamnose-mannose disaccharide
The lipopolysaccharides present in bacterial cell wall has lipid A connected to both the core polysaccharide and O-polysaccharide (O-antigen). This SEO-optimized article answers the MCQ: The lipopolysaccharides present in bacterial cell wall has lipid A which is connected to (A) O-polysaccharide, (B) core polysaccharide, (C) both O-polysaccharide and core polysaccharide, (D) rhamnose-mannose disaccharide—essential for microbiology and biotechnology students studying Gram-negative cell walls.
Correct Answer: Option (C) Both O-polysaccharide and Core Polysaccharide
Lipid A anchors LPS in the outer membrane via its glucosamine disaccharide phosphorylated at 1 and 4′ positions with six fatty acyl chains. Lipid A connects directly to core polysaccharide (inner/outer KDO-heptose region) which then extends to O-polysaccharide (repeating antigenic units).
Full LPS structure: Lipid A → Core oligosaccharide → O-antigen. Lipid A provides endotoxin activity; core confers serum resistance; O-antigen enables serotype specificity.
Explanation of All Options
LPS architecture follows strict sequential assembly:
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(A) O-polysaccharide: Incorrect. Lipid A doesn’t directly connect to O-antigen; core polysaccharide intervenes.
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(B) Core polysaccharide: Partially correct but incomplete. Lipid A connects to core via KDO (3-deoxy-D-manno-octulosonic acid).
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(C) Both O-polysaccharide and core polysaccharide: Correct. Lipid A → core → O-chain complete structure.
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(D) Rhamnose-mannose disaccharide: Incorrect. No such specific linkage; core sugars vary (KDO, heptose, glucose).
Option Connection to Lipid A Accurate? LPS Region Role (A) O-polysaccharide Indirect (via core) No Surface antigen (B) Core polysaccharide Direct (KDO-linked) Partial Serum resistance (C) Both Complete structure Correct Full LPS function (D) Rhamnose-mannose None specific No Not universal Biotechnology Relevance
LPS extraction (hot phenol-water) and Lipid A detoxification critical for vaccine adjuvants and endotoxin removal in your mammalian cell culture (Q.5). Core-O antigen variation enables phylogenetic typing (Q.17) of fermentation strains (Q.12,15,16).
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