Porins and LPS

Porins
* the phospholipids that compose the outer membrane give it the same semi-permeable characteristics as the Cytoplasmic membrane.
* to transport medium-sized or charged molecules across, the molecules move through a porin, a water-filled channel or pore.
* Porins are chemically selective - transport only one group of molecules, or may be specific for one molecule.
* for antibiotics to be effective against a bacterium, it must pass through the outer membrane, using through a porin.
* bacteria can develop resistance to the antibiotic by mutating the gene that encodes the porin - the antibiotic is then excluded from passing through the outer membrane.
LPS
* LPS has both lipid and polysaccharide components.
* the “core polysaccharide” contains “KDO” - a highly negatively charged sugar. The outer membrane needs to be stabilized with calcium or magnesium ions.

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