2.1 Concept Check
All microbial cells have certain basic structures in common such as a cytoplasmic membrane, ribosomes and (usually) a cell wall. Two structural categories of cells are recognized: the prokaryote and the eukaryote. Viruses are not cells but depend on cells for their replicative functions.
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2.2 Concept Check
Genes govern the properties of cells, and a cell's complement of genes is referred to as its genome. DNA is arranged in cells to form chromosomes. In prokaryotes there is usually a single circular chromosome, while in eukaryotes, several linear chromosomes exist.
2.3 Concept Check
Ribosomal RNA sequencing has revolutionized microbiology and has yielded an evolutionary framework for the prokaryotes. The three domains of life are the Bacteria, the Archae, and the Eukarya have evolutionary roots in the Bacteria and has yielded new tools for microbial ecology and diagnostics.
2.4 Concept Check
Sources of energy and carbon are needed by all cells. The terms chemoorganotroph, chemolithotroph, and phototroph refer to cells that use organic chemicals, inorganic chemicals, or light, respectively, as their source of energy. Autotrophic organisms use CO2 as their carbon source. Many prokaryotes thrive under environmental conditions that humans would call extreme.
2.5 Concept Check
Several lineages are present in the domains Bacteria and Archae, and an enormous diversity of cell morphologies and physiologies are represented there. Retrieval and analysis of ribosomal RNA genes from cells in natural samples have shown that many phylogenetically distinct but as yet uncultured prokaryotes exist in nature.
2.6 Concept Check
Microbial eukaryotes are a diverse group that includes algae, protozoa, fungi, and slime molds. Some algae and fungi have developed mutualistic associations called lichens.