Prokaryotic cell systems

Host system Prokaryotes Eukaryotes Cell- free systems... 

From the very earliest times these anaerobic prokaryote cells had assembled fundamental organic chemicals as outlined in Table 4.4, but as we have stressed in Chapters 3 and 4, to be viable, each cell type had to have also certain inorganic systems in place and had developed features such as... 

Genotoxic Effects. No studies were located regarding the genotoxic effects of hexachloroethane in humans after inhalation, oral, or dermal exposure. In vitro studies of hexachloroethane using microbial, fungal, and rodent cell assays are summarized in Table 2-4. Tests of prokaryotic cell systems failed to detect gene mutation (Haworth et al. 1983 Roldan-Arjona et al. 1991 Simmon and Kauhanen 1978 ... 

The Producing System. The questions of particular concern here are the nature of the system used to manufacture the desired substance, and the precision with which it is controlled. If the system consists of prokaryotic cells, then how well-defined is their provenance and how is their consistency demonstrated If mammalian cells are employed, their lineage must be considered. In both instances, it is important to ensure that extraneous virus, infections, DNA and less well-defined factors such as slow viruses are excluded by the origins and history of the producer strain, or because the physical (e.g., filtration) or chemical (pH, solvents, affinity separation) nature of the production process can be relied upon to exclude passage of an infectious agent. 

Although all tetracyclines have a similar mechanism of action, they have different chemical structures and are produced by different species of Streptomyces. In addition, structural analogues of these compounds have been synthesized to improve pharmacokinetic properties and antimicrobial activity. While several biological processes in the bacterial cells are modified by the tetracyclines, their primary mode of action is inhibition of protein synthesis. Tetracyclines bind to the SOS ribosome and thereby prevent the binding of aminoacyl transfer RNA (tRNA) to the A site (acceptor site) on the 50S ri-bosomal unit. The tetracyclines affect both eukaryotic and prokaryotic cells but are selectively toxic for bacteria, because they readily penetrate microbial membranes and accumulate in the cytoplasm through an energy-dependent tetracycline transport system that is absent from mammalian cells. 

In eukaryotic systems, challenges intrinsic to NMR (e.g., low sensitivity or proper discrimination between target and background signals) become even more pronounced. Interesting applications of NMR to eukaryotic systems are developing that study important cellular features like posttranslational protein modification or directed transport that are not observed in prokaryotic cells (150). 

The control of cellular proliferation and differentiation in response to external stimuli is achieved by signal transduction pathways, which are regulated in part by the co-ordinated action of protein kinases and phosphatases. In eukaryotic cells the protein kinases involved fall primarily into two classes, those that phosphorylate tyrosine residues and those that are specific for serine and threonine residues. Prokaryotic cells also rely on protein phosphorylation cascades for regulation of cellular activities, but the kinases involved are primarily histidine kinases, which are part of the sensing domain of two-component regulatory systems. These histidine kinases and their associated response regulators are involved in a range of adaptive responses by bacteria. 

Table I shows the distribution of silica in biological systems. In direct contrast to the abundance of siliceous structures observed in lower plants and animals, no silicified structures have been observed in bacteria. Why this should be so is not clear however, because siliceous structures in unicellular organisms require the synthesis of special membrane-bound compartments, the lower structural organization of prokaryotic cells may be an important factor inhibiting the formation and organization of silica in these organisms.

Eukaryotic systems. In eukaryotic cells and organisms, reporter genes similar to those used for prokaryotic cells can be utilized, although for some genes optimized, mutated versions have been developed. 

The second system was discovered in prokaryotic cells a few years ago [22]. It is the recently characterized non-heme iron superoxide reductase (SOR) that catalyzes the reduction of 02 into H2O2 by an intracellular reductant ... 

The codon AUG has two functions. It corresponds to the amino acid methionine when AUG occurs within a coding sequence in the mRNA, i.e., within a polypeptide chain. It also serves as a signal to initiate polypeptide synthesis—with methionine for eukaryotic cells but with N-formylmethionine for prokaryotic cells. How the protein-synthesizing system distinguishes an initiating AUG from an internal AUG is discussed below. The codon GUG also has both functions, but it is only rarely used in initiation. Once initiation has occurred at an AUG codon, the reading frame is established and the subsequent codons are translated in order. 

Q.2.3 Are the sub-systems described in Question 2.2 the same for the prokaryotic cells and for the eukaryotic cells ... 

---