Multiple Choice
Which of the following best explains the presence of nontransformed bacteria growing on an LB/ampicillin (LB/amp) plate during a transformation experiment?
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7. Prokaryotic Cell Structures & Functions
Introduction to Bacterial Cell Walls
Multiple Choice
Which of the following statements correctly describes the difference between Lipid A and O antigen in the structure of Gram-negative bacterial cell walls?
A
Lipid A is a polysaccharide, while O antigen is a lipid.
B
Both Lipid A and O antigen are found only in Gram-positive bacteria.
C
O antigen is responsible for toxicity, while Lipid A determines antigenic specificity.
D
Lipid A is the toxic component of lipopolysaccharide, while O antigen is the variable, antigenic polysaccharide portion.
Verified step by step guidance1
Understand the structure of the Gram-negative bacterial outer membrane, which contains lipopolysaccharide (LPS) molecules composed of three main parts: Lipid A, core polysaccharide, and O antigen.
Recognize that Lipid A is a lipid component embedded in the outer membrane and is responsible for the toxic effects (endotoxin activity) of LPS.
Know that the O antigen is a polysaccharide chain extending outward from the core polysaccharide and varies among bacterial strains, providing antigenic specificity.
Distinguish that Lipid A is not a polysaccharide but a lipid, and O antigen is not a lipid but a polysaccharide, which helps clarify the incorrect statements.
Conclude that the correct description is: Lipid A is the toxic component of LPS, while O antigen is the variable polysaccharide portion responsible for antigenic specificity.
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