Cell rupture

Once the cellular materials are separated, those with intracellular proteins need to be ruptured to release their products. Disruption of cellular materials is usually difficult because of the strength of the cell walls and the high osmotic pressure inside. The cell rupture techniques have to be very powerful, but they must be mild enough so that desired components are not damaged. Cells can be ruptured by physical, chemical, or biological methods. 

Physical Methods Physical methods include mechanical disruption by milling, homogenization, or ultrasonication. Typical high-speed bead mills are composed of a grinding chamber filled with glass or steel beads which are agitated with disks or impellers mounted on a motor-driven shaft. The efficiency of cell disruption in a bead mill depends on the concentration of the cells, the amount and size of beads, and the type and rotation speed of the agitator. The optimum wet solid content for the cell suspension for a bead mill is typically somewhere between 30 percent to 60 percent by volume. The amount of beads in the chamber is 70 percent to 90 percent by 

An ultrasonicator generates sound waves above 16 kHz, which causes pressure fluctuations to form oscillating bubbles that implode violently generating shock waves. Cell disruption by an ultrasonicator is effective with most cell suspensions and is widely used in the laboratory. However, it is impractical to be used on a large scale due to its high operating cost. 

Chemical Methods Chemical methods of cell rupture include the treatment of cells with detergents (surfactants), alkalis, organic solvents, or by osmotic shock. The use of chemical methods requires that the product be insensitive to the harsh environment created by the chemicals. After cell disruption, the chemicals must be easily separable or they must be compatible with the products. 

Surfactants disrupt the cell wall by solubilizing the lipids in the wall. Sodium dodecylsulfate (SDS), sodium sulfonate, Triton X-100, and sodium taurocholate are examples of the surfactants often employed in the laboratory. Alkali treatment disrupts the cell walls in a number of ways including the saponification of lipids. Alkali treatment is inexpensive and effective, but it is so harsh that it may denature the protein products. Organic solvents such as toluene can also rupture the cell wall by penetrating the cell wall lipids, swelling the wall. When red blood cells or a number of other animal cells are dumped into pure water, the cells can swell and burst due to the osmotic flow of water into the cells. 

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The biological activity of penicillins and cephalosporins is due to the presence of the strained /3-lactam ring, which reacts with and deactivates the transpeptidase enzyme needed to synthesize and repair bacterial cell walls. With the wall either incomplete or weakened, the bacterial cell ruptures and dies. 

Fig. 19. Variation of exposure time associated with cell rupture and the threshold shear stress for various systems [112]...

Reverse osmosis can be used to purify water, because the liquid passing through the semipermeable membrane is pure solvent. A water purifier that uses reverse osmosis requires semipermeable membranes that do not rapture under the high pressures required for reverse osmosis. Recall that seawater has an osmotic pressure of nearly 28 atm and that red blood cells rupture at 7 atm. Nevertheless, membranes have been developed that make it feasible to purify water using this technique. Reverse osmosis currently supplies pure drinking water to individual households as well as entire municipalities. 

The initial step after cellular uptake of T4 is metabolic transformation to 3,5,3, -tri-iodothyronine (T3) (Fig. 52-8), which interacts with cytosolic and nuclear receptors, as well as with synaptosomal membrane binding sites of unknown function [25], Cytosolic receptors are proteins of 70 kDa that do not appear to undergo translocation to cell nuclei, nor do they appear to be nuclear proteins that have leaked out of cell nuclei during cell rupture nuclear receptors are proteins of 50 70 kDa that have both DNA-and hormone-binding domains [25,26,28],... 

Different factors contribute to the mechanical properties of plant tissue cell turgor, which is one of the most important ones, cell bonding force through middle lamella, cell wall resistance to compression or tensile forces, density of cell packaging, which defines the free spaces with gas or liquid, and some factors, also common to other products, such as sample size and shape, temperature, and strain rate (Vincent, 1994). Depending on the sample properties (mainly turgor and resistance of middle lamella), two failure modes have been described (Pitt, 1992) cell debonding and cell rupture. 

The Florey-Chain team s investigation showed that penicillin interferes with the cell wall of bacteria. Bacteria cells ruptured instead of continuing to grow. In 1938, their animal test, on eight mice given lethal doses of infectious bacteria, showed stunning results. The four mice with penicillin survived, whereas four controls with no medication died. Their first human patient who suffered from infection showed early improvement with penicillin, but died subsequently when the stock of penicillin was exhausted. 

Mealiness in apples results from a breakdown in adhesion between cells so that chewing the apple tissue results in cell separation rather than cell rupture. Eating a mealy apple is therefore associated with the unpleasant sensory perception of a lack of juiciness, loss of crispness and hardness. A number of studies have succeeded in correlating the degree of mealiness with destructive reference tests such as the Magness-Taylor firmness and confined compression juiciness, but clearly there is a need for non-destructive, on-line detection of mealiness in apples. 

Alfalfa Lysis. Whole alfalfa (Medicago sativa) plant tissue was broken and cell rupture was by shear in a rotary device. Juice expression was by a batch type press, as described elsewhere (17), The resulting alfalfa extract was stored, until required, at -20°C. 

Histological examination of the liver reveals extensive cen-trilobular necrosis with loss of characteristic architecture of the hepatic cords. TEM examination indicated that both hepatocytes and hepatic endothelial cells were destroyed. The only alterations noted prior to cell rupture were slight mitocondrial swelling and slight cell swelling. Damaged cells had extensive fragmentation and vesiculation of the membrane (34). 

Hemolysis is the leakage of hemoglobin into liquid such as plasma, and is due to disruption of the erythrocytes. Within the body, hemolysis maybe caused by some diseases or poisons, whereas hemolysis outside the body, as in artificial organs, is caused by physical or chemical factors. If erythrocytes are placed in water, hemolysis will occur as the cells rupture due to the difference in osmotic pressure between water and the intracellular liquid. Hemolysis in artificial organs and their accessories occurs due to a variety of physical factors, including turbulence, shear, and changes of pressure and velocity. It is difficult, however, to obtain any quantitative correlation between the rates of hemolysis and such physical factors. 

Alternatives to grinding include explosive depressurization, which is involved in the Iotech (5) and Masonite (16) processes, ultrasonics (17), osmotic cell rupture, and conventional chemical pulping techniques. Explosive depressurization appears especially promising because of its effectiveness and relatively low energy consumption. 

Cell rupture may not be necessary to achieve effective pretreatment. The effectiveness of irradiation (1) with electrons or gamma rays may be due in part to riddling the cells with holes. Depolymerization of the cell membrane to expose the contents is another noncell-rupture approach. 

Foam structures consist of at least two phases, a plastic matrix and gaseous voids or bubbles. A closed-cell or open-cell structure is formed, with cellular walls enclosing the gaseous voids. In closed cell foams, the gas cells are completely enclosed by cell walls, while in open-cell foams, the dispersed gas cells are unconfined and are connected by open passages. Plastic can be stabilized against cell rupture by crosslinking (Chapters 1 and 2). 

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