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 Ca or Mg ions.

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