Permeability cell respiration

These gas- and water-impermeable cell layers protect the plant from desiccation, but they also hamper the uptake of carbon dioxide necessary for photosynthesis and oxygen necessary for respiration. Specialized tissues have evolved to allow passive (lenticels) and active (guard cells) modification of the permeability of the external cuticle to gas exchange. 

Mechanism of Action An electrolyte that is essential for the function and integrity of the nervous, muscular, and skeletal systems. Calcium plays an important role in normal cardiac and renal function, respiration, blood coagulation, and cell membrane and capillary permeability. It helps regulate the release and storage of neurotransmitters and hormones, and it neutralizes or reduces gastric acid (increase pH). Calcium acetate combines with dietary phosphate to form insoluble calcium phosphate. Therapeutic Effect Replaces calcium in deficiency states controls hyperphosphatemia in end-stage renal disease. 

In eukaryotic cells, electron transport and oxidative phosphorylation occur in mitochondria. Mitochondria have both an outer membrane and an inner membrane with extensive infoldings called cristae (fig. 14.2). The inner membrane separates the internal matrix space from the intermembrane space between the inner and outer membranes. The outer membrane has only a few known enzymatic activities and is permeable to molecules with molecular weights up to about 5,000. By contrast, the inner membrane is impermeable to most ions and polar molecules, and its proteins include the enzymes that catalyze oxygen consumption and formation of ATP. The role of mitochondria in 02 uptake, or respiration, was demonstrated in 1913 by Otto Warburg but was not fully confirmed until 1948, when Eugene Kennedy and Albert Lehninger showed that mitochondria carry out the reactions of the TCA cycle, the transport of electrons to 02, and the formation of ATP. 

Lehninger, A.L., 1974, Role of phosphate and other proton-donating anions in respiration-coupled transport of Ca2+ by mitochondria, Proc. Natl. Acad. Sci. USA 71, pp. 1520-1524 Lehninger, A.L., Carafoli, E., and Rossi, C. S., 1967, Energy-linked ion movements in mitochondrial systems, Adv. Enzymol. Relat. Areas. Mol. Biol. 29, pp. 259-320 Lemasters, J.J., Nieminen, A. L., Qian, T., Trost, L., Elmore, S. P., Nishimura, Y., Crowe, R. A., Cascio, W. E., Bradham, C. A., Brenner, D. A., and Herman, B., 1998, The mitochondrial permeability transition in cell death A common mechanism in necrosis, apoptosis and autophagy, Biochim. Biophys. Acta 1366, pp. 177-196... 

Copper is an essential element. Copper plays a significant role in several physiological processes - photosynthesis, respiration, carbohydrate distribution, nitrogen reduction and fixation, protein metabolism, and cell wall metabolism. Many plant metalloenzymes contain copper. It also influences water permeability of xylem vessels and thus controls water relationships. It is mainly complexed with organic compounds of low molecular weight and with proteins (Henze and Umland, 1987). Kabata-Pendias and Pendias (1984) have compiled data on the Cu concentrations in... 

Phenolic acids are known to alter photosynthetic and respiration rates, cause stomatal closure, reduce chlorophyll content, modify the flow of carbon into various metabolic pools, and alter nutrient uptake in affected tissue (61-73). A common denominator for these multiple effects appears to be the action of phenolic compounds on membranes. They are soluble in membranes, and cause a reduction in ion accumulation in cells (71-73). Several phenolic acids cause membrane depolarization, especially at low pH, increasing membrane permeability to ions (72,73). This action undoubtedly impairs the proton gradient and ATP-driven ion transport. Logically, the effects phenolic acids have on membranes could disturb the water balance and mineral nutrition of seedlings, and research in my laboratory has established such a relationship. 

The potential toxicity of OH-PCBs was first investigated in the 1970s. Hydroxylated metabolites were reported having higher potencies for cell toxicity than their parent PCBs [64,193]. Phenolic PCB metabolites were also found to affect mitochondrial respiration and the permeability of the inner membrane. The nature of the effect depended on the structure and pKa of the phenolic metabolite [110,194]. Low binding potencies toward the aryl hydrocarbon receptor (AhR), and low induction capacity of ethoxyresorufin-O-deethylase (EROD), respectively, have been reported for phenolic PCB metabolites of non-ortho CB-77 and mono-ortho CB-105 [34, 195]. Dihydroxylated PCBs may be oxidized to quinones that in turn may react with macromolecules to form adducts, and cause oxidative stress leading to cell death [116]. 

The transfer of the information described in the preceding sections of this chapter to the in vivo situation is a matter where opinions are sharply divided, even if more than 20 years have elapsed since the discovery by Vasington and Murphy [4]. One key problem, naturally, is the impossibility of reproducing the composition and the conditions of the cytosol in in vitro experiments. The above mentioned effect of Mg on the rate of Ca influx into mitochondria is but one striking example of the difficulties inherent to the extrapolation to the in situ conditions. Of interest in this respect are recent experiments [124,125] in which methods have been devised to estimate simultaneously the membrane potential across the plasma membrane and the mitochondria of nerve endings in situ. The conclusion of this work has been that the concentration of free Ca in the cytosol correlates directly to the membrane potential across the mitochondrial membrane, and is maintained at a steady-state level below 1 jaM. Simulation of the in situ conditions has also been the aim of studies [126] in which isolated liver endoplasmic reticulum has been added to media in which isolated liver mitochondria were made to take up Ca, or in which liver cells have been treated with digitonin to abolish the permeability barrier of the plasma membrane. It was found that respiring mitochondria lower the external Ca " concentration to about 0.5 /iM. The addition of endoplasmic reticulum vesicles produces a further decrease of the external Ca " to about 0.2 jaM. Thus, mitochondria... 

The essential element, hypoperfusion of vital organs, is present whatever the cause, whether pump failure (myocardial infarction), maldistribution of blood (septic shock) or loss of total intravascular volume (bleeding or increased permeability of vessels damaged by bacterial cell products, bums or anoxia). Fimction of vital organs, brain (consciousness, respiration) and kidney (urine formation) are clinical indicators of adequacy of perfusion of these organs. 

Aerobic respiration, a process by which cells use 02 to generate energy, takes place in mitochondria. Each mitochondrion is bounded by two membranes. The smooth outer membrane is permeable to most molecules with masses less than 10,000 D. The inner membrane, which is impermeable to ions and a variety of organic molecules, projects inward into folds that are called cristae. Embedded in this membrane are structures called respiratory assemblies that are responsible for the synthesis of ATP. 

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