General Characteristics of Viruses
General Characteristics of most viruses demonstrate a number of common properties:
- molecular (non-cellular) structure.
- the viral genome represents only the one type of nucleic acid – DNA or RNA that indicates DNA or RNA viruses, respectively; viral nucleic acids can be organized as double-stranded or single-stranded.
- viruses are obligate intracellular parasites capable of propagating solely in the living cells.
- viruses are devoid of molecular structures for protein synthesis; the infected cell provides energy and ribosomal apparatus for successful viral propagation (synthesis of proteins and nucleic acids, viral assembly, etc.)
- viruses are the minute microorganisms, ranging from about 15-20 nm to 400 nm in most cases; viral particles are able to pass through the filter membranes, retaining the majority of bacterial cells.
- viruses demonstrate highly intensive genetic variability; the phylogenesis of viruses is governed by the laws of evolution.
- viruses are ubiquitous in nature; they can multiply in bacteria, algae, fungi, and protozoa as well as in plants and animals.
- viruses are not affected by antibiotics; viral infections are treated by a special class of antiviral drugs.
- The host range for a certain virus may be wide or extremely limited. Usually, viruses can interact only with the cells of a few related species.