Lipopolysaccharide (LPS) is a molecule located in the outer leaflet of the outer membrane of gram-negative bacteria. During infections involving these bacteria, LPS functions as an endotoxin, contributing to severe symptoms such as fever, hemorrhaging, and septic shock. Structurally, each LPS molecule is composed of Lipid A, a core polysaccharide, and an O side chain.

Lipopolysaccharide (LPS)

Murein lipoprotein is a structural molecule that attaches the outer membrane to the peptidoglycan layer within the complex cell envelope of gram-negative bacteria.

Murein Lipoprotein

In gram-negative bacteria, the outer membrane is a distinct second lipid bilayer situated exterior to the thin peptidoglycan layer of the cell envelope. This membrane is firmly anchored to the underlying peptidoglycan by murein lipoprotein. A key feature of its outer leaflet is the presence of lipopolysaccharide (LPS), a complex molecule comprising an O antigen, core polysaccharide, and lipid A with attached fatty acid tails, which acts as an endotoxin during bacterial infections.

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Gram-negative cells possess a cell envelope with a significantly thinner layer of peptidoglycan—no more than about $${}4$$ nm thick—compared to gram-positive cells. Their overall cell envelope structure is highly complex, featuring a periplasmic space and an outer membrane located external to the peptidoglycan layer.

Gram Negative Cell Walls

Al-mohanna, Moshtaq & H., quine. (2016). MORPHOLOGY AND CLASSIFICATION OF BACTERIA. 

Morphology and Classification of Bacteria

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

The periplasmic space in gram-negative cells is the region located between the peptidoglycan cell wall and the plasma membrane. It is occupied by a gel-like matrix, adding to the structural complexity of the gram-negative cell envelope.

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