Eukaryotic cells, specific enzyme production

The best known functions of the ER require a high membrane surface and/or a separate, specific microenvironment within the organelle. Although many enzymes hosted by the ER use its membranous structure only as a scaffold, others are compartmentalized within the ER i.e., their active site is localized in the lumen. The activity of these enzymes usually is dependent on the special composition of the luminal compartment. The enzymes often receive their substrates and cofactors from or release their products to the cytosol therefore, the transport of these compounds across the ER membrane is indispensable. This article focuses on this latter group of the ER enzymes, the functioning of which makes the ER a separate metabolic compartment of the eukaryotic cell. 

Among the replicative differences between eukaryotic cells (of the viral host) and the pathogenic virions is that the latter need virus-dependent proteinases to produce the mature infectious virus. That is, HIV protease is an essential enzyme utilized by the virus to process proteins in order to reproduce itself. Retroviruses (and RNA viruses) produce the structural and enzymic proteins as large multidomain polyproteins. The specific cleavage of these various domains into the final products is a posttranslational event. These end-products enable the virion to develop into the actual infectious agent (Kransslich and Wimmer, 1988). 

Energy production in mitochondria and the mechanisms behind cell division are very similar in all eukaryotic organisms. Furthermore, some inhibitors of enzymes have so little specificity that many different enzymes in a great variety of organisms may be targets. Many of the pesticides with such general modes of action have considerable historic interest. Not all of them are simple in structure, and many are used for purposes other than combating pests. 

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