nucleic acid - viral genes are made up of either
DNA or RNA and the nucleic acid may be either single
stranded (ss) or double stranded (ds)
capsid - protein coat made up of subunits called
capsomeres
Envelope
membrane derived from host cell as the virus
leaves the cell during the process of budding
only certain animal viruses (the ones that are
released from the host cell by budding) have
envelopes, and these viruses require them for virion
integrity
Reproduction - occurs only inside host cells and is
called replication
Attachment - to receptor sites on host cell by
spikes (peplomers)
Penetration - entrance into host cell
Uncoating - removal of capsid(s); frees the viral
genes to be expressed
Biosynthesis - synthesis of viral DNA or RNA and
proteins
Maturation - components assemble to form viral
particles (virions)
Release - virions "emerge" from the host cell by
lysis or "budding"
Importance and Habitat - pathogenic; ubiquitous,
function only inside living cells
Groups of Viruses
Bacterial Viruses (Bacteriophages) - consequences of virus
infection of a bacterial host cell include:
Lytic Infection - bacteriophage replication cycle
Attachment occurs as the virus binds to surface
structures of the host bacterium
Penetration and uncoating (occur
simultaneously) as the viral nucleic acid, but not the
capsid, enters the bacterium
Synthesis leads to the generation of nucleic acid
and protein components of the progeny virions
Assembly of the viral nucleic acid and proteins
to generate the mature virions
Release is caused by viral lytic enzymes
Lysogeny
Bacteriophage DNA integrates into the host
chromosome after penetration/uncoating
No progeny virions are made unless an inducer (UV
light, certain chemicals) triggers release of bacteriophage
DNA from the host chromosome, thus initiating the lytic
replication cycle, generating progeny virions
Animal Viruses - consequences of virus infection of a
animal host cell include:
Lytic infection - viral nucleic acid initiates
destructive replication cycle in which progeny virions are
produced and the host cell is destroyed
Attachment occurs as the virus binds to surface
structures called receptors of the host cell -
spikes (peplomers) on the viral surface
mediate this interaction
Penetration occurs as the virus enters the cell
Enveloped viruses fuse their envelope with the
cytoplasmic membrane of the host cell to enter
Nonenveloped viruses are generally taken into
the host cell by phagocytosis
Uncoating occurs as not the capsid(s) is(are)
removed by host cell digestive enzymes, thus releasing the
viral nucleic acid
Synthesis leads to generation of viral nucleic
acid and protein components using the information coded in
the original viral nucleic acid (this can be complicated,
and the mechanism by which it occurs depends on whether the
nucleic acid is DNA or RNA and whether it is single- or
double-stranded
Assembly of the viral nucleic acid and proteins
to generate the mature virions
Release is caused by viral lytic enzymes, or by
budding in the case of enveloped viruses
Persistent infection &endash; host cell remains
alive and produces progeny virions at a slow rate, but for a
long time
Latent infection &endash; there is a delay between
infection of the host cell and generation of progeny
virions
Transformation &endash; the viral nucleic acid
triggers neoplastic changes in the host cell which
"immortalilze" it and cause uncontrolled growth, which can lead
to tumors (cancer) in the host
benign tumor &endash; noninvasive
malignant tumor - invasive
Plant Viruses - consequences of virus infection of a plant
host cell include:
Similar in most respects to those seen for animal
cells
Penetration is more difficult for plant viruses than
it is for animal viruses because plant cells have cell
walls
