Viral replication cycles

One characteristic viruses share in common with true living organisms is the need to reproduce themselves . As we have seen, all viruses are obligate intracellular parasites, and so in order to replicate, a host cell must be successfully entered. It is the host cell

Table 10.2 Major groupings of viruses based on the Baltimore system

Group I

dsDNA viruses

Group II

ssDNA viruses

Group III

dsRNA viruses

Group IV

(+) sense ssRNA viruses

Group V

( —) sense ssRNA viruses

Group VI

Single-stranded (+) sense RNA with DNA intermediate

Group VII

Double-stranded DNA with RNA intermediate

* Since the processes involved proceed at the molecular rather than the organismal level, it is more appropriate to speak of viral replication than of reproduction.

* Since the processes involved proceed at the molecular rather than the organismal level, it is more appropriate to speak of viral replication than of reproduction.

Virus families always end in '-viridae',subfamiliesin '-virinae' and genera in '-virus'. Such names are italicised and capitalised, whereas this is not done for species. e.g. Order: Monone-gavirales, Family: Para-myxoviridae, Subfamily: Paramyxovirinae, Genus: Morbillivirus, Species: measles virus. For informal usage, we would talk about, for example, 'the picornovirus family', or the 'enterovirus genus'.

An indication of just how complex the taxonomy of viruses can be is given by the fact that in 1999, a paper was published in a leading virologyjour-nal, entitled: 'How to write the name of virus species'!

Assembly M Replication

Figure 10.7 Main stages in a viral replication cycle. The replication cycle of all viruses is based on this generalised pattern

Assembly M Replication

Figure 10.7 Main stages in a viral replication cycle. The replication cycle of all viruses is based on this generalised pattern that provides much of the 'machinery' necessary for viral replication. All viral growth cycles follow the same general sequence of events (Figure 10.7), with some differences from one type to another, determined by viral structure and the nature of the host cell.

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