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
RNA
Envelope (withglycoproteins)
Capsid and viral genomeenter the cell
HOST CELL
Viral genome (RNA)
Template
mRNA
ER
Glyco-proteins
Capsidproteins 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. 19-8aGlycoprotein
Reversetranscriptase HIV
RNA (twoidenticalstrands)
Capsid
Viral envelope
HOST CELL
Reversetranscriptase
Viral RNA
RNA-DNAhybrid
DNA
NUCLEUS
Provirus
ChromosomalDNA
RNA genomefor thenext viralgeneration
mRNA
New virus
Fig. 19-8b
HIVMembrane ofwhite blood cell
HIV entering a cell
0.25 µm
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
(b) Influenza A H5N1 virus
(c) Vaccinating ducks
0.5 µm
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
Prion
Normalprotein
Originalprion
Newprion
Aggregatesof prions
Misfolding of proteins to form prions
Scrapie in sheep
