General Characteristics of Viruses

General Characteristics of  most viruses demonstrate the 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 of the cases; viral particles are able to pass through the filter membranes, retaining the majority of bacterial cells.
• viruses demonstrate highly intensive genetic variability; 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.