Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 64

 Many distinct functions of the host cell are required to complete a viral infectious cycle.

 The synthesis of new virus particles (i.e., a productive infection) requires target cells that are both susceptible (i.e., allow virus entry) and permissive (i.e., support virus reproduction).

 Viral nucleic acids must be shielded from harsh environmental conditions in extracellular particles but be readily accessible for replication once inside the cell.

 Viruses may be studied by propagation in cells within a laboratory animal or in cells in culture.

 The plaque assay is the major way to determine the concentration of infectious virus particles in a sample.

 Methods for quantifying and characterizing virus particles evolve rapidly, based on developments in detection, ease, cost, safety, utility in the field, and amenability to large-scale implementation.

 Relationships among viruses can be deduced from phylogenetic trees generated from protein or nucleic acid sequences.

 Viral reproduction is distinct from cellular or bacterial replication: rather than doubling with each cycle, each single cell cycle of viral reproduction is typically characterized by the release of many (often thousands) of progeny virions.

 The multiplicity of infection (MOI) is the number of infectious units added per cell; the probability that any one target cell will become infected based on the MOI can be calculated from the Poisson distribution.

 Global analysis of viral, cell, and host responses to virus infection can implicate particular cellular pathways in viral reproduction and can reveal signatures of virus-induced lethality or immune protection.

Figure 2.1 The viral infectious cycle. The infectious cycle of poliovirus is shown as an example, illustrating the steps common to most viruses: attachment and entry, translation, genome replication, particle assembly, and release. See Appendix, Fig. 22, for explanation of abbreviations. Inset: Lipid components of the plasma membrane. The membrane consists of two layers (leaflets) of phospholipid and glycolipid molecules. Their fatty acid tails converge to form the hydrophobic interior of the bilayer; the polar hydrophilic head groups (shown as balls) line both surfaces.