Q.68 Which part of the lipopolysaccharides has toxic properties that make some bacterial
infections a potentially serious medical problem?
(A) Polysaccharide side–chains (B) Lipid A portion
(C) Repeat carbohydrate units (D) Core region of polysaccharides
The toxic properties in lipopolysaccharides (LPS) that make some bacterial infections serious come from the Lipid A portion. This is the endotoxin component in Gram-negative bacteria’s outer membrane, triggering severe immune responses like septic shock. The correct answer is (B) Lipid A portion.
Option Analysis
Lipopolysaccharides consist of three main parts: Lipid A, core polysaccharide, and O-antigen side chains. Each option relates to these, but only one drives toxicity.
-
(A) Polysaccharide side-chains: These are O-antigen chains providing serological specificity and immune evasion, but they lack toxicity.
-
(B) Lipid A portion: This phosphorylated glucosamine disaccharide with fatty acids anchors LPS and acts as the endotoxin, binding TLR4 to cause inflammation, fever, and shock.
-
(C) Repeat carbohydrate units: These refer to repeating O-antigen oligosaccharides for strain variation, not toxicity.
-
(D) Core region of polysaccharides: The core oligosaccharide (with KDO and heptose) links Lipid A to O-antigen for membrane stability, without toxic effects.
Lipopolysaccharides toxic properties stem from Gram-negative bacteria’s outer membrane, turning infections into medical emergencies via endotoxins. Understanding lipopolysaccharide toxic properties is crucial for CSIR NET Life Sciences, as Lipid A triggers hyperactive immune responses.
LPS Structure Breakdown
LPS comprises Lipid A (toxic anchor), core oligosaccharide (inner linker), and polysaccharide side-chains (O-antigen).
-
Lipid A: Fatty acid-linked glucosamine responsible for endotoxin activity.
-
Core region: Contains KDO sugars for stability, non-toxic.
-
Side-chains: Repeat units for antigenic diversity.
Toxicity Mechanism
Lipid A binds TLR4/CD14, releasing cytokines like TNF-α, leading to fever, inflammation, and septic shock in severe cases. Polysaccharide parts aid immunity but do not cause harm.
Exam Relevance
For CSIR NET, questions test LPS components: Lipid A as the toxic endotoxin, distinguishing it from non-toxic polysaccharide regions. Gram-negative infections highlight its role in pathogenicity.
