Lipopolysaccharides

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Lipopolysaccharides (pronunciation: li-po-po-ly-sac-cha-rides) are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, and elicit strong immune responses in animals.

Etymology

The term Lipopolysaccharides is derived from three components: Lipo from Greek lipos meaning fat, poly from Greek polys meaning many, and saccharide from Greek sakcharon meaning sugar. Thus, the term literally means many sugars and fats.

Structure

Lipopolysaccharides are composed of an O-antigen, a core oligosaccharide, and a lipid A. The O-antigen and the core oligosaccharide are both composed of various sugars, while the lipid A is a lipid.

Function

Lipopolysaccharides play a crucial role in the structural integrity of bacteria, and protect the membrane from certain kinds of chemical attack. They also play a key role in the immune response, as they are recognized by the immune system as foreign substances.

Related Terms

  • Endotoxin: Lipopolysaccharides are considered endotoxins, as they are released when the bacteria die and the cell walls disintegrate.
  • Gram-negative bacteria: These bacteria are characterized by their cell walls that contain lipopolysaccharides.
  • Immune response: The body's defensive reaction to invasion by bacteria, other foreign substances, or injury.
  • Lipid: One of the three main types of nutrients. Lipids are fats and oils.
  • Polysaccharide: A carbohydrate that is composed of sugar molecules.

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