Cellular organelle

Ion Channels. The excitable cell maintains an asymmetric distribution across both the plasma membrane, defining the extracellular and intracellular environments, as well as the intracellular membranes which define the cellular organelles. This maintained a symmetric distribution of ions serves two principal objectives. It contributes to the generation and maintenance of a potential gradient and the subsequent generation of electrical currents following appropriate stimulation. Moreover, it permits the ions themselves to serve as cellular messengers to link membrane excitation and cellular... 

Fourier Transform Infra Red Spectroscopy, Arrhenius plots of rate vs. temperature of a membrane-linked phenomenon) that biological membranes from nonhibemat-ing or cold acclimated animals show a phase transition around 12 °C to 17 °C. Thus, at useful cold storage temperatures, it is expected that the plasma membrane and membranes of the cellular organelles will be mostly in a gel or solid state. 

To correlate embryonic arrests with the metabolic pathways, and especially to understand why cellular organelles first undergo chemical damages, biological investigations include evaluation of DNA, RNA, protein, glucose, lipid, and adenosine-5 -triphosphate (ATP) contents, whose fractions are extracted and isolated by modified Schneider methods. In particular,... 

Sub-cellular fractionation of five strains reveal the same numbers of bands. The distribution of PG activity in sub-cellular organelles was broadly similar in these five strains. PG activity was detected in low-density vesicles, vacuoles and ER fractions in samples harvested during the early exponential phase of growth. However, PG levels were always lower (at least 1.5 fold) than those found in wild type. Cells of the mutants harvested during stationary phase of growth showed that 84% of total intracellular PG activity was located in the vesicle fraction. No intracellular PG activity was found in stationary phase wild type cells. 

This process of gene transfer, called lateral gene transfer (LGT), does not seem to have stopped at the borders of cellular organelles and nucleus, either. LGT may explain incongruous patterns of inheritance for some... 

Lipid peroxidation is probably the most studied oxidative process in biological systems. At present, Medline cites about 30,000 publications on lipid peroxidation, but the total number of studies must be much more because Medline does not include publications before 1970. Most of the earlier studies are in vitro studies, in which lipid peroxidation is carried out in lipid suspensions, cellular organelles (mitochondria and microsomes), or cells and initiated by simple chemical free radical-produced systems (the Fenton reaction, ferrous ions + ascorbate, carbon tetrachloride, etc). In these in vitro experiments reaction products (mainly, malon-dialdehyde (MDA), lipid hydroperoxides, and diene conjugates) were analyzed by physicochemical methods (optical spectroscopy and later on, HPLC and EPR spectroscopies). These studies gave the important information concerning the mechanism of lipid peroxidation, the structures of reaction products, etc. 

Table 3.13 Density gradient ultracentrifugation of sub-cellular organelles Organelle Density (p)...

Biocatalysts Enzymes Microbial, plant, animal cells Sub-cellular organelles... 

Many methods for the fractionation of cellular organelles have been described and it is probably not possible to have a method that is equally effective at preserving each individual component. For each type of cell and organelles the most appropriate method must be selected and evaluated. 

These marker enzymes are assumed to be associated with only one of the cellular organelles and hence their relative concentrations in each fraction will give some indication of the degree of cross-contamination in the preparations. There is considerable debate about the validity of this assumption and more precise information may be gained from specialist texts. 

What are the enzymes associated with sub-cellular organelles known as ... 

Recently, we also documented that PS oxidation during oxidant-induced apoptosis occurred within the plasma membrane, the largest source of oxidized PS compared to other cellular organells (Kawai et al, 2000). 

The structure of an alphavirus particle is simpler than that of all known cellular organelles, but it is built according to the same principles. This is because the viral genome is small and the virus must use for its construction those cellular components normally engaged in the biogenesis of host cell membranes. This means that studies of viral replication can be exploited to study cellular functions at the molecular level. Naturally viral infections also perturb cellular physiology, but there is usually enough time early in infection for studies to be carried out before cellular malfunction becomes a source of error. 

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