Which statement about lipopolysaccharide (LPS) is true?

• A. It is found in Gram-positive bacteria
• B. It is a lipid that stabilizes the outer membrane
• C. It is a nucleic acid
• D. It is unique to Gram-negative bacteria

Answer: (D)

Lipopolysaccharide is a distinctive component of the outer membrane of Gram-negative bacteria. It’s a large molecule made up of three parts: lipid A that anchors the LPS to the membrane, a core polysaccharide, and an O-antigen that sticks outward. Because Gram-negative bacteria have this outer membrane rich in LPS, while Gram-positive bacteria lack that membrane and do not contain LPS, the statement that LPS is unique to Gram-negative bacteria is true. It’s not a nucleic acid, and it isn’t simply a lipid—it's a complex glycolipid with polysaccharide components, so describing it as just a lipid would be an oversimplification.