Eukaryotes coupled

The ability of dyneins to effect mechano-chemical coupling—i.e., motion coupled with a chemical reaction—is also vitally important inside eukaryotic cells, which, as already noted, contain microtubule networks as part of the cytoskele-ton. The mechanisms of intracellular, microtubule-based transport of organelles and vesicles were first elucidated in studies of axons, the long pro-... 

Despite the limited information available, rather clear predictions can be made about the probable structure, location, and energy coupling of the amino acid transporters of Saccharomyces cerevisiae, by comparing them with better known systems in both prokaryotes and eukaryotes. 

Ono Y, Fujibuchi W, Suwa M. Automatic gene collection system for genome-scale overview of G-protein coupled receptors in eukaryotes. Gene 2005 364 63-73. 

For the internalisation of metals, many examples exist for which transport may be coupled to an energy-dependent process, of which only a few are described here. For example, the well-studied (e.g. [276]) Na+/K+ channel transports 3Na+ out and 2K+ in for each ATP molecule that is hydrolysed [242]. Mg2+ influx (but likely not efflux) is highly regulated in eukaryotes [277]. ATPases have been implicated in certain cases of Fe [278] or Zn [90] uptake by phytoplankton. Finally, although Cd internalisation by a polychaete appeared to be energy independent, accumulation was increased rather than decreased in the presence of ATPase inhibitors, suggesting that the efflux system might depend upon ATP synthesis [279]. 

The next process is similar in both eukaryotes and prokaryotes, and involves the translation of mRNA molecules into polypeptides. This procedure involves many enzymes and two further types of RNA transfer RNA (tRNA) and ribosomal RNA (rRNA). There is a specific tRNA for each of the amino acids. These molecules are involved in the transportation and coupling of amino acids into the resulting... 

Eukaryotic ABC transport system Phosphotransferase system (PTS) Ion-coupled transport system Signal Transduction Two-component system Bacterial chemotaxis MAPK signaling pathway Second messenger signaling pathway Ligand-Receptor Interaction G-protein-coupled receptors Ion-channel-linked receptors Cytokine receptors Molecular Assembly Ribosome assembly Flagellar assembly Enzyme assembly... 

Technically, in vitro transcription is achieved from standard expression plasmids typically carrying SP6 or T7 promoters using marketed kits. Translation into the polypeptide may be either coupled directly to the transcription (in vitro TnT) or require isolation of the RNA. Again, a large number of suitable prokaryotic and eukaryotic cell extracts as well as complementation factors are freely available. 

Cytochrome bci is a multicomponent enzyme found in the inner mitochron-drial membrane of eukaryotes and in the plasma membrane of bacteria. The cytochrome bci complex functions as the middle component of the mitochondrial respiratory chain, coupling electron transfer between ubiquinone/ ubiquinol (see Figure 7.27) and cytochrome c. 

Cytochrome c and ubiquinol oxidases are part of an enzyme superfamily coupling oxidation of ferrocytochrome c (in eukaryotes) and ubiquinol (in prokaryotes) to the 4 e /4 reduction of molecular oxygen to H2O. After this introduction, we will concentrate on the cytochrome c oxidase enzyme. The two enzymes, cytochrome c oxidase (CcO) and ubiquinol oxidase, are usually defined by two criteria (1) The largest protein subunit (subunit I) possesses a high degree of primary sequence similarity across many species (2) members possess a unique bimetallic center composed of a high-spin Fe(II)/(III) heme in close proximity to a copper ion. Cytochrome c oxidase (CcO) is the terminal... 

More recently, we have extended this study of strand asymmetries in intron sequences to evolutionarily distant eukaryotes [37]. When appropriately examined, all genomes present transcription-coupled excess of T over A ( TA > 0) in the coding strand. In contrast, GC skew is found positive in... 

M. Touchon, A. Arneodo, Y. d Aubenton-Carafa, and C. Thermes, Transcription-coupled and splicing-coupled strand asymmetries in eukaryotic genomes. Nucl. Acids Res. 32, 4969-4978... 

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