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