Cells, animal classification

Classification of animal viruses Most of the animal viruses which have been studied in any detail have been those which have been amenable to cultivation in cell cultures. As seen, animal viruses are known with either single-stranded or doublestranded DNA or RNA. Some animal viruses are enveloped, others are naked. Size varies greatly, from those large enough to be just visible in the light microscope, to those so tiny that they are hard to see well even in the electron microscope. In the following sections, we will discuss characteristics and manner of multiplication of some of the most important and best-studied animal viruses. 

In the 1990s, ECVAM held a forum to vet and evaluate new alternative assays, and developed a list of compounds for testing (24). The key driver for this activity was the fact that DART studies require large numbers of animals. The primary focus of this activity was embryo-fetal toxicity. The list generated from this forum was tested in three assays (later validated by ECVAM) (1) the micromass assay, (2) the rat WEC assay, and (3) the embryonic stem cell test (25). Compounds on the Brown list were classified as either strong, weak, or non-teratogens. The three assays successfully predicted the compound classification about 80% of the time. However, the embryonic stem cell test later performed poorly on a different group of chemicals with known in vivo activities (26). 

Lipids, relatively nonpolar chemical substances found in plant, bacterial, and animal cells, are among the most ubiquitous of biomolecules. In this experiment, a lipid extract of ground nutmeg will be purified by chromatography on a silica gel column. Analysis of the lipid extract by thin-layer chromatography will provide the classification of the components in the extract. The unknown lipids will be further characterized by saponification and analysis of the fatty acid content by gas chromatography. For an abbreviated experiment, students may be provided samples of natural oils and fats that can be analyzed by saponification and gas chromatography. 

The different operation modes used in microbial fermentations are employed also in animal cell cultivation. Although many different classifications can be adopted, the most general is the one that considers the following operation modes batch, fed-batch, continuous, and perfusion, which is a continuous mode with cell recycle/retention (Castilho and Medronho, 2002). 

Enzyme Preparations used in food processing are derived from animal, plant, or microbial sources (see Classification, below). They may consist of whole cells, parts of cells, or cell-free extracts of the source used, and they may contain one active component or, more commonly, a mixture of several, as well as food-grade diluents, preservatives, antioxidants, and other substances consistent with good manufacturing practices. 

Two types of regulatory approvals exist for medical devices in the United States, 510(k) notification and premarket approval (PMA). The types of tests required for approval depend on the classification of the medical device. 510(k) notification involves marketing a device that is substantially equivalent to a device on the market prior to 1976. All devices introduced after 1976 that are not substantially equivalent to devices on the market before 1976 are automatically classified as Class 3 devices and require PMA (16). For a device fo be considered subsfantially equivalenf to a device on the market before 1976, it must have the same intended use, no new technological characteristics, and have the same performance as one or more devices on the market prior to 1976. In addition, all medical devices must be sterilized either by end-sterilization or by some other acceptable means that can be validated, which means that any test done in cell culture or in an animal model must be conducted on a device that has been validated to be sterile. Sterility validation is conducted on all medical devices as described in the literature (17). 

To arrive at a classification, test results are considered from experiments determining mutagenic and/or genotoxic effects in germ and/or somatic cells of exposed animals. Mutagenic and/or genotoxic effects determined in in vitro tests may also be considered. 

The antimicrobial antibiotics have a selectively toxic action on invading bacteria, by virtue of exploiting differences in cellular characteristics between microorganisms and their human host cells. Major target sites are the bacterial cell wall located outside the cell membrane (animal cells have only a cell membrane). and the bacterial ribosome - the protein-synthesizing organelle within its cell - which is different between bacteria and animal cells. Viruses lack both cell walls and ribosomes and so are resistant to these and other similar antibiotics. A classification of therapeutically used antibiotics can be attempted on the basis of these mechanisms. 

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