Bacteria, cell membrane nucleic acid content

The abnormal deposits found in the brains of CJD victims consist of an abnormal isoform of PrP. Prion protein is normally found in cells. Detailed structural studies show that normal cellular PrP (PrP ) is a soluble protein whose conformation is rich in a-helices with very little P-sheet. The PrP protein extracted from the brains of CJD victims (i.e., PrP ) is identical in primary amino acid sequence to the normal PrP (PrP ). However, PrP has a much greater content of P-sheet conformation with little a-helical structure. Thus PrP is neurotoxic because of its three-dimensional structure. When the prion protein is predominantly in an a-helical conformation it is nontoxic when the prion protein is predominantly in a P-sheet conformation, it kills neurons. The prion protein is thus made neurotoxic not by its amino acid composition but by its conformation. This concept is both fascinating and terrifying. Prion diseases are transmissible thus prions are infectious agents. However, prions are not like bacteria or viruses, or other infectious microbes—they are simply protein molecules. Prions are not microbes with cell membranes and nucleic acids they are not living things. Indeed, prions are not even infectious molecules, they are infectious molecular shapes. 

Since bacteria make up 60 to 90% of the intestinal contents, they cannot in principle be toxic. Pathogenicity and toxicity may be caused by certain cell substances, e.g. lipopolysaccharides which vary from strain to strain. Therefore, conclusions concerning the suitability of bacteria for human nutrition can only be drawn from an extensive program involving many bacterial strains which have been grown as monocultures without contamination. Furthermore, other cell fractions, such as proteins, cell walls, cytoplasmic membranes, pure storage materials, and nucleic acids must also be tested. 

A membrane in a cell wall fulfills a number of functions. It acts as a barrier to prevent the contents of a cell from dispersing and also to exclude external agents such as viruses. The membrane, however, does not have a purely passive role. It also enables the transport of ions and chemicals such as proteins, sugars and nucleic acids into and out of the cell via the membrane proteins. Membranes are important not only as the external cell wall, but also within the cell of eukaryotes (plants and animals, but not most bacteria) where they subdivide the cell into compartments with different functions. 

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