Among clinically relevant microorganisms, bacterial cells are prokaryotic, whereas cells of parasites and fungi are eukaryotic, as are those of plants and all higher animals. Viruses are acellular and depend on host cells for survival.
A notable characteristic of eukaryotic cells, such as those of parasites and fungi, is the presence of membrane-enclosed organelles that have specific cellular functions. Examples of these organelles and their respective functions include:
Additionally, eukaryotic cells have an infrastructure, or cytoskeleton, that provides support for the different organelles.
Prokaryotic cells, such as those of bacteria, do not contain organelles. All functions take place in the cytoplasm or cytoplasmic membrane of the cell. Prokaryotic and eukaryotic cell types also differ considerably at the macromolecular level regarding protein synthesis machinery, chromosomal organization, and gene expression. One notable structure present only in bacterial cells that is absent among eukaryotes is a cell wall composed of peptidoglycan. As is mentioned many times over in this text, this structure alone has immeasurable impact on the practice of diagnostic bacteriology and the management of bacterial diseases.
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