nd its trademark dumbbell shaped capsid. (B) Compared to the ~200 nanometer length of
smallpox, the ~30 nanometer non-enveloped poliovirus is
... [Show More] significantly smaller. (C)
Paramyxovirus, the causative agent of measles/mumps contains a single-stranded, linear
(albeit twisted and clumped) genome compared to the eight RNA segments of the
orthomyxovirus (flu) show in (D).
The smallpox virus (variola virus) is enveloped, about 200 nm long, and has a
distinct dumbbell-shaped viral capsid (Figure 6.1A)
The poliovirus is non-enveloped and only about 30 nm in diameter (Figure
6.1B)
Although electron microscopes images are capable of resolving the
differences in the shape of the virus, looks can be deceiving.
Paramyxoviruses and orthomyxoviruses are both enveloped, spherical, and
about 100-150 nm in diameter, but they vary drastically in composition and
function (Figure 6.1C and D)
Paramyxoviruses, the causative agent of measles and mumps, contain a
single-stranded linear genome and fuse with the host cell membrane to
initiate entry and viral replication
In contrast, orthomyxoviruses, the causative agent of the flu, contain eight
segments of RNA and enter the host cell via endocytosis
Figure 6.2 Generalized Viral Life Cycle. The virus must first attach to the host cell (1)
and quickly penetrate and enter the cell (2). The capsid disintegrates (uncoating), as it
enters the cytoplasmic space (3). The viral genome then undergoes transcription/translation
to produce new viral proteins (4) as well as duplicates its entire genome (5). New viruses are
then assembled (6) and released (7).
Figure 6.3 Bacteriophage. (A) The structural elements of a bacteriophage are shown. An
icosahedral head group is separated from the tail region by the collar, while the base plate
(fixed at the end of the tail) and tail fibers are located at the conclusion of the helical sheath.
(B) Viral DNA is injected into the host cell. [Show Less]