Which of the following statements correctly describes a lipopolysaccharide?

• A. It is found primarily in the cell wall of Gram-positive bacteria.
• B. It is a major component of the outer membrane of Gram-negative bacteria.
• C. It functions as the main energy source for bacterial metabolism.
• D. It consists of a lipid A, a core polysaccharide, and an O antigen.

Answer: (D)

Verified step by step guidance

1. Understand that lipopolysaccharides (LPS) are complex molecules found in bacterial cell envelopes, specifically associated with Gram-negative bacteria.
2. Recall the structural components of LPS: it is composed of three main parts — lipid A, which anchors the molecule in the outer membrane; the core polysaccharide; and the O antigen, which extends outward from the cell.
3. Recognize that LPS is a major component of the outer membrane of Gram-negative bacteria, contributing to the structural integrity and protection of the bacteria.
4. Note that LPS is not found in Gram-positive bacteria, which lack an outer membrane and instead have a thick peptidoglycan layer.
5. Understand that LPS does not serve as an energy source for bacteria; its primary roles are structural and immunological, such as triggering immune responses in hosts.