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109 Cards in this Set

  • Front
  • Back
What size are poxviruses?
250 nm

about the same size as chlamydiae and mycoplasmas in size (poxviruses are about as big as these smallest bacteria)
What size are parvoviruses?
20 nm

about the same diameter as DNA
100 nm is equal to how many um?

Viruses can't reproduce on its own. They must go in humans or some other host. In other words, viruses are ___
obligate intracellular parasites
Who discovered viruses in the early 1800's by looking at plant sap of tobacco?
Dmitri Ivanowsky
What are the 3 different shapes viruses come in?
What viruses fit under the category "helical viruses"?
Tobacco mosaic virus
Rabies virus
Measles virus
What viruses fit under the category "Icosahedral viruses"?
herpes simplex virus
polio virus
What viruses fit under the category "complex viruses"?
smallpox virus
influenza virus
All viruses consist of two basic components: a core of nucleic acid called the _____ and a surrounding coat of protein known as the ___
The genome contains ______; and the nucleic acid occurs in ______
either DNA or RNA, but not both

double-stranded or single-stranded form
ssDNA or ssRNA
dsDNA or dsRNA
The capsid is a surrounding ______ coat and it protects the genome
The capsid is subdivided into individual protein subunits called _____

The number of capsomeres is characteristic for a particular virus.
What are three things are important about the capsid?
1) characteristic # of capsomeres
2) gives shape to virus
3) protects genome
The capsid plus the genome is called the ____
Many viruses are surrounded by a _____ and _____ membrane known as an envelope
lipid and protein
Many viruses are surrounded by a lipid and protein membrane known as an ____
In some viruses, the envelope contains functional projections known as ____
Spikes contain ____ for attachment
No envelope, no ___
A completely assembled and infectious virus outside its host cell is known as a ___
A T4 bacteriophage is a complex virion with a head and a tail, but no ___
The best known process of replication in E. coli is that carried on by bacteriophages of the T-even group (T for "type"). Bacteriophages ___, ___, and ___ are in this group
T2, T4, T6
burst size
How many new phages are made at the conclusion of the replication process. (50 to 200 new phages emerge from the host cell)

(bacteriophage = virus)
What are the five stages of bacteriophage replication?
1) Attachment
2) Penetration
3) Biosynthesis
4) Maturation
5) Release
What happens during attachment?
The bacteriophage's tail or viral capsid attaches to its host cell (bacterium) at a complementary receptor site.
What happens during penetration?
The capsid remains outside the cell, while the viral genome enters the cell's cytoplasm.

(viral DNA injected intracellularly, capsid extracellular)
What happens during biosynthesis?
The viral genome encodes proteins for the synthesis of new viral parts. The cell's nucleic acid degrades
What happens during maturation?
New viruses are assembled from the newly synthesized capsids and genomes, usually in a step-by-step process.
What happens during release?
New viruses are released from the host cell to infect adjacent cells and begin a new cycle of replication.

(host destroyed, new viruses released)
burst time
The time that passes from phage attachment to the release of new viruses.
The method of replication displayed by T-even phages is similar to that in animal viruses, but with some notable exceptions. One example is the attachment phase. Like bacteriophages, animal viruses have attachment sites, but the receptor sites exist on the host _____ rather than the ____.
plasma membrane
cell wall
animal viruses have no tails, so the attachment sites often are the _____ distributed over the surface of the capsid or envelope
Penetration of T-even phages and animal viruses are also different. Phages inject their DNA into the host cell cytoplasm, but animal viruses usually are taken in toto (become one w/host cell) into the cytoplasm. What are the two methods of penetration?
1) spikes interact with host cell membrane
2) entire enveloped virus endocytosed
What happens in the method where spikes interact with the host cell membrane?
envolpe fuses with host cell membrane
What happens in the method where the entire enveloped virus is endocytosed?
envelope is removed in cytoplasm of host cell
The final steps of viral replication may include the acquisition of an envelope. In this step, envelope proteins are synthesized and incorporated into a nuclear or cytoplasmic membrane, or the plasma membrane. Then, the virus pushes through the membrane, forcing a portion of the membrane ahead of it and around it, resulting in an envelope. This process, called ____, need not necessariy kill the cell during the virus's exit. The same cannot be said for unenveloped viruses, however. They leave the cell when the cell membrane ruptures, a process that generally leads to cell death.
viruses with envelopes bud from the cell without ____
lysing host
Non-enveloped viruses rupture the ____
host cell membrane
____ and ____ DNA genomes are made in the host nucleus
Adenovirus and herpesvirus
Some DNA viruses employ a division of labor: DNA genomes are synthesized in the host cell nucleus, and capsid proteins are produced in the ____. The proteins then migrate to the nucleus and join with the nucleic acid molecules for assembly of nucleocapsid. The envelope comes from ____
nuclear membrane
Describe the process of the replication of a DNA Animal Virus that replicates in the host nucleus
1) The host cell membrane fuses with the viral envelope, thereby permitting entry of the nucleocapsid to the cytoplasm

2) The viral capsid is uncoated by cell enqymes, and the DNA of the viral genome enters the cell's nucleus

3) New viral DNA is synthesized in the nucleus resulting in new genomes. Transcription produces mRNAs that are translated on cytoplasmic ribosomes

4) Capsid proteins are synthesized in the cell's cytoplasm

5) Capsid proteins enter the nucleus and combine with viral genomes to form new nucleocapsids

6) The viruses bud through the nuclear envelope, endomembranes (for chickenpox), or plasma membrane to acquire their envelope before the mature virions are released
While adenoviruses and herpesviruses DNA genomes are made in the host nucleus, Other DNA viruses like ____ replicate in the host cytoplasm
The RNA can act as a messenger RNA molecule and immediately begin supplying the codes for protein synthesis. Such a virus is said to have "sense"; it is called a ______, or ____
positive-stranded RNA virus

sense virus

*Genome acts as mRNA, used as template for translation of viral proteins
*get in human host cell, genome is ready made for causing disease
Give an example of a + stranded RNA virus
polio virus
In some RNA viruses, however, the RNA is used as template to synthesize a complementary strand of RNA. The latter then is used as a messenger RNA molecule for protein synthesis. The original RNA strand is said to have "antisense," and the virus is therefore an _______ or a ______. Usually the enzyme RNA polymerase is present in the virus to synthesize the complementary strand.
antisense virus
negative-stranded RNA virus

*Viral-encoded RNA polymerase makes complementary strand of RNA, used as template for translation of viral proteins.
_______ makes complementary strand of RNA, used as template for translation of viral proteins.
Viral-encoded RNA polymerase
Give an example of a negative stranded (antisense) RNA virus
measles virus
Retroviruses carry their own enzyme, called ____
reverse transcriptase
Give an example of two Retroviruses
viral-encoded reverse transcriptase makes _____ from ____
ssDNA from RNA genome

RNA genome ---> reverse transcriptase ----> ssDNA
In the formation of a Provirus, a complementary strand is made to yield ____.

*THe virus penetrates the host cell. After uncoating, reverse transcription of the viral genome catalyzes the synthesis of double-stranded DNA.
Complementary strand made to yield dsDNA. Viral DNA integrates into host cell genome, becomes _____

*The new DNA is transported into the host cell's nucleus and integrated into the nuclear DNA as a provirus.
Viral DNA will incorporate into host cell genome, so can't figure out if it is foreign or not. THerefore, Provirus is immune to ______.
host cell antibodies. Antibodies cannot penetrate cells
A virus is replicated whenever ____
chromosome is copied
In the replication cycles, infection need not result in new viral particles or cell lysis. Rather, the virus may integrate its DNA or its RNA (via DNA) into a chromosome of the cell. When bacteriophages are involved, the phage DNA in the lysogenic state in a bacterial cell is called a prophage; when an animal virus (such as a retrovirus) is involved, the viral DNA is known as a ___
What are the 3 hypotheses for the origins of viruses?
1) Regressive Evolution Hypothesis
2) Cellular Origins Hypothesis
3) Independent Entities Hypothesis
Regressive Evolution Hypothesis
Viruses are degenerate life-forms; that is, they are derived from intracellular parasites that have lost many functions that other organisms possess and have retained only those genes essential for their parasitic way of life.
Cellular origins hypothesis
Viruses are derived from subcellular components and figured out how to replicate autonomously in host cells
Independent Entities Hypothesis
Viruses coevolved with cellular organisms from the self-replicating molecules beilieved to have existed in the primitive prebiotic earth
Why aren't antibiotics effective against viral infections?
1) viruses use host enzymes and machinery
2) Viruses have no cell walls
Viruses rely almost exclusively on the _____ for their replication
host cell's metabolic machinery
Because viruses rely almost exclusively on the host cell's metabolic machinery for their replication, it is difficult to ____
find targets of selective toxicity
What are two things most antiviral drugs do?
1) Disrupt critical stages of the virus life cycle

2) prevent synthesis of virus-specific nucleic acids
Most antiviral drugs disrupt critical stages of the virus life cycle. _____ blocks uncoating of influenza virus
What does amantadine do?
amantadine blocks uncoating of influenza virus. It stops the influenza virus at a step in its life cycle. It needs to uncoat, but can't now!
Amantidine blocks the uncoating of the influenza virus. It prevents/reduces the ____
severity and duration of disease
Most antiviral drugs prevent synthesis of virus-specific nucleic acids. _____ stops herpes infections by disrupting activity of virus-specific nucleic acid synthesis enzymes
What does vidarabine do?
Vidarabine stops herpes infections by disrupting activity of virus-specific nucleic acid synthesis enzymes
What are the four major classes of antiviral drugs?
base analogs
reverse transcriptase inhibitors
neuraminidase inhibitors
protease inhibitors
base analogs look like _____
Once base analogs are incorporated, it stops the _____
synthesis of nucleic acids
What base analog is used to treat genital herpes and chickenpox?
What base analog is used to treat HIV?
Azidothymidine (AZT)
What do reverse transcriptase inhibitors do?
binds and inhibits reverse transcriptase

No reverse transcriptase in our cells, so inhibitors inhibits reverse transcriptase. only targets retroviruses
What two reverse transcriptase inhibitors blocks replication of retroviruses?
What do Neuraminidase inhibitors do?
prevents attachment of influenza virus

Neuraminidase is an enzyme in the spike of the influenza virus. It helps the virus infect cells and, after replication, helps the viruses spread to other cells. The neuraminidase inhibitor drug zanamivir blocks the action of neuraminidase, preventing release of new virions--and thereby limiting disease spread in the body.
Name a neuraminidase inhbitor
What do protease inhibitors do?
These drugs react with protease, the enzyme that trims viral proteins down to working size for the construction of the capsid.

*protease function required for HIV capsid construction
Guve three examples of protease inhibitors
saquinivir, indinavir, and ritonavir looks like _______; therefore, they act as decoys
the peptide bond that is normally attacked by protease

protease (cuts up proteins) ---> protease inhibitors (decoys) --> won't attack capsid protein now. just attack protease inhibitors
What are interferons?
20 proteins produced by body cells in response to viral invasion. They provide protection against viruses.
Interferons stimulates the production of ______ that interfere with viral reproduction in neighboring cells
antiviral proteins
Describe the production and activity of interferon
A) Viral RNA stimulates the host to synthesize interferon while also directing replication of new viruses

B) Interferon is synthesized and released from the cell

C) viruses are released following replication

D) Interferon binds to a neighboring cell

E) Interferon induces the cell to express the genes for antiviral proteins

F) Antiviral proteins (AVPs) are synthesized

G) The antiviral proteins block viral protein synthesis and thus interfere with viral replication
Interferons are normally made by viruses. They can synthesize outside the body and work as ____
chemotherapeutic agents
What are prions?
proteinaceous infectious particles
What do prions cause?
kuru (cannibalism)

mad cow disease (bovine spongiform encephalopathy)
what is mad cow disease also known as?
bovine spongiform encephalopathy
What is the incubation period for prions?
8-12 yrs
Prions cause brain cells to develop ____
spongiform encephalopathies
Who studied the disease in sheep called scrapie?
Stanley Prusiner.
He found a protein in the brain. It wasn't a virus. How could the protein cause disease? PRION!
What don't prions have?
no nucleic acid
How are prions killed?

*no nucleic acid, killed by proteases
What can prions survive?
heat, radiation, and chemicals that viruses cannot
What is the symbol for the normal prion protein?
What does PrPc do?
It binds copper in the brain. Copper is required for superoxide dismutase which protects cells from oxygen free radicals
Copper is required for ______ which protects cells from oxygen free radicals
superoxide dismutase
What is the symbol for the normal prion in the wrong conformation?
PrPSC. Ingested misshapen prion may travel to brain and do what?
change normal prion proteins- cause disease
What is needed for diagnosis and confirmation?
brain biopsy
The nerve cell, ____, wants to get the bad prion (PrPsc). It clumps it together. It can't destroy the prions. prions kill the nerve cell and leaves a space. get spongiform.
The influenza virion belongs to the _____ family of viruses.
The influenza virus is composed of eight _____, each would helically and associated with protein to form a nucleocapsid

*normally single genome. now in influenza. eight different genomes; therefore, a segmented genome. each genome is covered in proteins
_____ surrounds each helix
______ surrounds the core of segments
matrix protein
______ surrounds matrix protein
Projecting from the envelope is a series of spikes that contain ______
H spike stands for ____