Bacteria cell membranes

Polymyxin B Bacillus polymyxa Gram-negative bacteria Cell membrane... 

The extraction procedure used to isolate lipids from biological tissue depends on the class of lipid desired and the nature of the biological source (animal tissue, plant leaf, plant seed, bacteria, cell membranes, etc.). Because lipids are generally less polar than other cell constituents, they may be selectively extracted with the use of organic solvents. Early studies of lipids used ether, acetone, hexane, and other organic solvents for extraction however, these solvents extract only lipids bound in a nonpolar or hydrophobic manner. In the 1950s, Folch s group reported the use of chloroform and methanol (2 1) in... 

Helenius and Simmons (1975) discussed the solubilization of bacteria cell membranes with detergents or surfactants, and Nixdorff (1978) discussed the interaction of lipopolysaccharides with detergents and the possible role in the detergent resistance of the outer membranes of gram-negative bacteria. 

Carbohydrates and saccharides are the fuels for cell metabolism. They also form important extracellular structural elements, such as cellulose (plant cells), and have other specialized functions. Bacteria cell membranes are protected by cell walls of covalently bonded polysaccharide chains. Human cell membranes are coated with other saccharides. Some saccharides form a jellylike substance filling the space between cells. Some polysaccharides may have a negative charge at a pH of 7, but many carbohydrates are not believed to contribute dominantly to the admittivity of tissue. 

The macrolides are bacteriostatic or bactericidal in susceptible bacteria The drugs act by binding to cell membranes and causing changes in protein function. 

Natamycin is a fungicide used to keep cheese from getting moldy. It works by making holes in the cell membranes of fungi, so their insides leak out. It is produced by Streptomyces natalensis bacteria. 

Immunologic abnormahties (eg, transfusion reactions, the presence in plasma of warm and cold antibodies that lyse red blood cells, and unusual sensitivity to complement) also fall in this class, as do toxins released by various infectious agents, such as certain bacteria (eg, Clostridium). Some snakes release venoms that act to lyse the red cell membrane (eg, via the action of phospholipases or proteinases). 

Fig. 9.1 Schematic representation of possible mechanisms of resistance in Gram-negative and Gram-positive bacteria. 1, antibiotic-inactivating enzymes 2, antibiotic efflux proteins 3, alteration or duplication of intracellular targets 4, alteration of the cell membrane reducing antibiotic uptake 5, alterations in porins or lipopolysaccharide reducing antibiotic uptake or binding.

A technique utilizing genetically modified bacteria to report the presence of particular compounds in soil has also been developed (37). These bacteria respond to the presence of specific compounds in their environment by producing ice-nucleation proteins that enter into cell membranes, enabling cells to be detected by means of a droplet freezing assay. The presence of trytophan in 1-10 i molar concentrations has been detected using reporter bacteria in a study examining loss of amino acids from roots of Avena barbata into soil (38). 

Polycationic polymers. These are macromolecules that have electropositive groups attached to the polymer chain or pendant to the chain. These materials are active against a number of bacteria and fungi. However, due to their inherent toxicity to animal species through their destructive interaction with cell membranes they are... 

The primary function of the B lymphocytes is to produce antibodies, which are molecules that identify and lead to the destruction of foreign substances such as bacteria. The B lymphocytes and the antibodies they produce are responsible for humoral immunity. T lymphocytes provide immunity against viruses and cancer cells. These lymphocytes directly attack and destroy their targets by forming holes in the target cell membrane, causing cell lysis. The T lymphocytes are responsible for cell-mediated immunity. 

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