Viruses Flashcards
found he could transfer plant diseases by rubbing sap extract from diseased to healthy plants.
Conclusion: Disease is caused by small bacteria invisible under a microscope.
1883, Germany
Adolf Mayer
filtered sap from infected tobacco leaves, but sap still caused mosaic disease. o Conclusion: Bacteria small enough to pass thru filter caused the mosaic disease.
1890, Russia
Dimitri Ivanowsky
sap filtered thru bacterium-trapping filter. Filtered sap still caused the disease. Pathogen could replicate within the host.
Conclusion: The pathogen is not a bacterium but a replicating particle; generally credited for the concept of a virus.
1898, Netherlands
Martinus Beijernick
crystallized the infectious particle.
Confirmed the particle as the causative agent now called the Tobacco Mosaic Virus (TMV); viruses examined under EM. Viruses were detected long before they were seen.
1935, USA
Wendell Stanley
are not cells. They are particles. o Opportunist particles (alive when they attach to a living host)
Viruses
is a very small infectious particle consisting of nucleic acid (DNA or RNA) enclosed in a protein coat and, in some cases, a membranous envelope.
Viruses
The protein coat of a virus is called a
capsid
Capsids are built from protein subunits called
capsomeres
CAPSID STRUCTURES
Helical
Icosahedral
Membranous envelopes
Elongates icosahedral head with tail
CAPSID STRUCTURES
rigid rod-shaped capsid with a thousand molecules of single type protein arranged in a helix, as in TMV.
Helical
with 252 identical protein molecules arranged in a polyhedral shape with 20 triangular facets, e.g., Adenoviruses.
Icosahedral
derived from membranes of the host cell (with host’s phospholipids and membrane proteins + viral proteins and glycoproteins) e.g., influenza viruses.
Membranous envelopes
most complex; head encloses the DNA protein tail with fibers attaches to bacterial host; found in viruses that infect bacteria, bacteriophages or phages
Elongates icosahedral head with tail
Viral genomes may consist of either:
Double- or single-stranded DNA (dsDNA, ssDNA)
Double- or single-stranded RNA (dsRNA, ssRNA)
Depending on its type of nucleic acid, a virus is called a
DNA virus or an RNA virus.
The ______ of a virus is either a single linear or circular molecule of the nucleic acid.
genome
Viruses have between three and several thousand genes in their genome.
Bacteria contain 200 to a few thousand genes.
true
no envelope
double stranded dna
Respiratory viruses; tumor- causing viruses
Adenovirus
no envelope
double stranded dna
Warts, cervical cancer
Papillomavirus
no envelope
double stranded dna
Warts, cervical cancer tumors
Polyomavirus
single stranded rna serves as ____ to make a lot of copies of the virus
messenger rna
Single-Stranded RNA (ssRNA)
no envelope
Rhinovirus (common cold); po- liovirus; hepatitis A virus; other intestinal viruses
Picornavirus
envelope
Single-Stranded RNA (ssRNA)
Severe acute respiratory syndrome (SARS)
Coronavirus
envelope
Single-Stranded RNA (ssRNA)
Yellow fever virus; West Nile virus; hepatitis C virus
Flavivirus
envelope
Single-Stranded RNA (ssRNA)
Yellow fever virus; West Nile virus; hepatitis C virus
Togavirus
Serves as Template for mRNA Synthesis
ssRNA
ssRNA
envelope
Measles virus; mumps virus
Paramyxovirus
ssRNA
envelope
Human immunodeficiency virus (HIV/AIDS; see Figure 19.8); RNA tumor viruses (leukemia)
Retrovirus
Virus Taxonomy The ICTV has changed its Code (ICTV 2018) to allow a _____________ classification hierarchy that closely aligns with the Linnaean taxonomic system. This new structure can accommodate the entire spectrum of genetic divergence in the virosphere.
fifteen-rank
Increase in transmissibility or detrimental change in virus epidemiology; or Increase in virulence or change in clinical disease presentation; or Decrease in effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics.
Variants of Concern
is a pathogen’s or microorganism’s ability to cause damage to a host.
virulence
compared to a reference isolate, its genome has mutations with established or suspected phenotypic implications, and has been identified to cause community transmission/ multiple cases/clusters, or has been detected in multiple countries.
Variants of Interest
Viruses replicate only in
host cells
Viruses are ________, which means they can replicate only within a host cell.
obligate intracellular parasites
a limited number of host cells that it can infect, following a lock-and-key fit between the viral surface proteins and the receptor molecules of the host cell.
host range
west Nile virus and equine encephalitis virus can each infect mosquitoes, birds, horses, humans are examples what range
Broad host ranges:
virus can infect only humans, or one species, what range
Narrow host ranges:
the viral DNA that is integrated into the host genome.
Prophage
the viral DNA that is permanently integrated into the host genome.
Provirus
are the best understood of all viruses
phages
Phages have two reproductive mechanisms:
Lytic cycle
Lysogenic cycle
is a phage replicative cycle that culminates in the death of the host cell
produces new phages and lyses (breaks open) the hosts cell wall, releasing the progeny viruses
LYTIC CYCLE
A phage that reproduces only by the lytic cycle is called a
virulent phage
__________ have defenses against phages, including restriction enzymes that recognize and cut up certain phage DNA
Bacteria
replicates the phage genome without destroying the host.
The viral DNA molecule is incorporated into the host cell’s chromosomes.
Every time the host divides, it copies the phage DNA and passes the copies to daughter cells.
LYSOGENIC CYCLE
This integrated viral DNA is known as a
prophage
An ___l can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode
environmental signa
Phages that use both the lytic and lysogenic cycles are called
temperate phages
Viruses do not fit our definition of living organisms Since
viruses can replicate only within cells
viruses are said to evolve from
bits of cellular nucleic acid
Candidates for the source of viral genomes include:
Plasmids
Transposons
small fragments of circular DNA.
Plasmids
class of genetic elements that can “jump” to different locations within a genome. (=jumping genes).
Transposons
Plasmids, transposons, and viruses are all mobile genetic elements.
true
HOW DO VIRUSES CAUSE DISEASES IN ANIMALS?
Damage or kill cells by causing the release of hydrolytic enzymes from lysosomes.
* Cause infected cells to produce toxins that lead to disease symptoms.
Have molecular components such as envelope proteins that are toxic.
TREATMENT AGAINST VIRUSES
Vaccines
Antiviral drugs
Defense frontline
Viral infections cannot be treated by antibiotics.
true
are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen.
can prevent certain viral illnesses.
Vaccines
Antiviral drugs can help to treat, though not cure, viral infections.
true
viruses that suddenly become apparent.
EMERGING VIRUSE
are caused by new strains of influenza virus to which people have little immunity
Flu epidemics
Viral diseases in small, isolated population can emerge and become global.
true
New viral diseases can emerge when viruses spread from animals to humans .
Viral strains that jump species can exchange genetic information with other viruses to which humans have no immunity
(zoonotic)
Most plant viruses have an RNA genome. Many have helical capsid, while others have an icosahedral capsid.
true
Plant viruses spread disease in two major modes:
Horizontal transmission
Vertical transmission
plant virus entering through damaged cell walls
Horizontal transmission
plants inheriting the virus from a parent
Vertical transmission
Smaller and simpler than viruses but as pathogenic as viruses.
VIROIDS AND PRIONS
are circular RNA molecules that infect plant.
Viroids
ex of viroids
Cadang-cadang caused deaths of 10 million coconut trees in the Philippines.
are slow acting (10 yrs incubation) virtually indestructible infectious proteins that cause brain diseases in mammals.
propagate by converting normal proteins into the prion version
Prions
