Characteristics of the Pathogenic Prokaryotes
Bacteria share the common characteristic of being prokaryotic (proto = primitive, karyos = nucleus). Prokaryotes, preceding the evolution of eukaryotic cells by two billion years, are single-celled organisms that have developed a diverse array of life forms that dominate our planet (Mathieu and Sonea, 1995). Unlike eukaryotic organisms, prokaryotes lack a defined nucleus. The genetic information of bacteria, approximately a thousand times less than in eukaryotic cells, is contained within a single, covalently closed, double-stranded (ds) DNA molecule, which is not partitioned from the cytoplasm by a nuclear membrane. In addition to chromosomal DNA, bacteria also possess small, self-replicating DNA molecules termed plasmids or prophages. Additional structural and biochemical properties distinguish prokaryotes from eukaryotes (Table 5–1; see Chapter 8). Prokaryotes lack the cytoskeletal elements (microtubules) and membrane-associated organelles (Golgi, mitochondria or chloroplasts, endoplasmic reticulum) which are characteristic of eukaryotic cells (Fig. 5–1). Ribosomes of prokaryotes are of the 7OS type (except Archaeobacteria), whereas eukaryotic cells possess the 8OS type. Bacteria reproduce by binary fission and do not require the spindle formation characteristic of the eukaryotic mitotic cell division. The majority of bacteria possess a rigid cell wall, which is chemically distinct from the cell walls found in certain eukaryotic cells.
KeywordsOuter Membrane Pathogenic Bacterium Negative Bacterium Positive Bacterium Host Insect
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