Teichoic acid
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Teichoic acids are polymers of glycerol or ribitol linked via phosphodiester bonds. These acids can be found in the cell wall of gram-positive bacteria and appear to extend to the surface of the peptidoglycan layer. Teichoic acids are not found in the gram-negative bacteria. They can be either covalently bonded to N-acetylmuramic acid of the peptidoglycan layer or linked to the plasma membrane lipids found in the cytoplasmic membrane. The combined units comprised of teichoic acids and lipids are referred to as lipoteichoic acids. Teichoic acids are negatively charged and therefore contribute to the negative charge of the gram-positive cell wall. They may also provide structural support for the cell wall.