Transcript RNA

Animal Viruses
• Because viruses are lifeless partials, their spread
depends on other agents.
• A(
) is an intermediate host that transfers a
pathogen or parasite to another organism
• Classified as (
) or (
) viruses, (
) or (
)stranded
• Many have envelopes with glycoproteins that are
specific for receptors.
• The glycoproteins are made by the ER and added to
the host cell’s membrane which envelopes the
emerging viruses.
Fig. 19-7
Capsid and viral genome
enter the cell
Capsid
RNA
HOST CELL
Envelope (with
glycoproteins)
Viral genome (RNA)
Template
mRNA
Capsid
proteins
ER
Glycoproteins
Copy of
genome (RNA)
New virus
Table 19-1a
Table 19-1b
RNA Viruses
• The broadest variety of RNA genomes is
found in viruses that infect animals
• (
) use (
) to copy their
RNA genome into DNA (HIV is ex.)
• The viral DNA that is integrated into the
host genome is called a (
)
• Unlike a prophage, a provirus remains a
permanent resident of the host cell
Fig. 19-8a
Glycoprotein
Viral envelope
Capsid
Reverse
transcriptase
RNA (two
identical
strands)
HOST CELL
HIV
Reverse
transcriptase
Viral RNA
RNA-DNA
hybrid
DNA
NUCLEUS
Provirus
Chromosomal
DNA
RNA genome
for the
next viral
generation
New virus
mRNA
Fig. 19-8b
HIV
Membrane of
white blood cell
0.25 µm
HIV entering a cell
New HIV leaving a cell
Viral diseases in animals
• Symptoms caused by
- toxins
- body’s defense mechanisms
• (
) – weakened or derivatives of
viral particles capable of causing an
immune response
• (
) not effective
• Some antiviral medications interfere
with viral (
) synthesis
Where do new viruses come
from?
•(
) of existing viruses
• The dissemination of an existing
virus to a more widespread
population
• Or spread between species
•(
) – general outbreak of a
disease
•(
) – global epidemic
Fig. 19-9
(a) The 1918 flu pandemic
0.5 µm
(b) Influenza A
H5N1 virus
(c) Vaccinating ducks
Plant viruses
• More than 2,000 types of viral diseases of
plants are known and cause spots on
leaves and fruits, stunted growth, and
damaged flowers or roots
• Most plant viruses have an RNA genome
• Plant viral disease can spread by vertical
transmission from parent plant or by
horizontal transmission from an external
source.
Fig. 19-10
Viroids and Prions: The Simplest
Infectious Agents
• (
) are circular RNA molecules that infect
plants and disrupt their growth
• (
) are slow-acting, virtually indestructible
infectious misfolded proteins that cause brain
diseases in mammals
• Prions propagate by converting normal
proteins into the prion version
• Scrapie in sheep, mad cow disease, and
Creutzfeldt-Jakob disease in humans are all
caused by prions
Viroids in Plants
Fig. 19-11
Misfolding of proteins to form prions
Prion
Normal
protein
Original
prion
New
prion
Aggregates
of prions
Scrapie in sheep