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60 terms

Microbiology Chapter 13

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virus
tiny infectious agent with nucleic acid surrounded by capsomeres
capsomeres
protein subunits of capsids that surround viruses
common characteristics of viruses, viroids, and prions
lack cell structure
cannot metabolize, grow or self-produce
cannot respond to the environment
capsid
the coating of protein surrounding the nucleic acid of a virus
virion
a complete viral article, including a nucleic acid and a capsid, outside of a cell
bacteriophage
a virus that infects a bacterial cell
How are viruses classified?
type of nucleic acid,
presense of an envelope,
shape,
size
5 stages of the replication cycle of a virus
attachment, entry, synthesis, assembly, release
Viruses depend on _________________.
random contact with a specific host cell type for replication
uncoating
process by which the capsid is removed after the virion enters the cell
latency
animal virus remains inactive in a cell as part of a chromosome or in the cytosol
provirus
the viral DNA which inserts into a host cell's chromosome
dsDNA virus
in a virus, acts like cellular DNA in transcription and replication
ssRNA virus
has positive-strand RNA which can be directly translated by ribosomes to synthesize protein
positive-strand RNA
same polarity as MRNA so genome RNA can be translated in cytoplasm by host cell ribosomes
negative-strand RNA
complementary to mRNA, genome must be transcribed by viral RNA polymerase to produce viral RNA
neoplasia
uncontrolled cell reproduction in a multicellular animal
tumor
mass of neoplastic cells
neoplastic cells
Tumor (abnormal function, unregulated growth
"steals nutrients from other tissues")
oncogenic virus
viruses that lead to cancer by permanently altering its genetic material
How are viruses cultured in a lab? Why?
inside mature organisms or embryonated chicken eggs, because viruses cannot metabolize or replicate alone
plaques on the bacterial lawn
clear areas on a agar plate where bacteria has been infected with phages lyse
phages
viruses that infect bacteria
lyse
to burst
plaque assay
Determines the number of viruses in solution. A known volume of solution is added to metabolizing cells, and the infection lyses cells and leads to a clear zone or plaque surrounded by uninfected cells. Each plaque represents one virion.
2 types of cell cultures on which viruses can be grown
diploid cell cultures and
continuous cell cultures
diploid cell cuture
last 100 generations
continuous cell cultures
derived from cancer cells, last longer than diploid cell cutures
viroids
small circular pieces of RNA with no capsid that infect and cause disease in plants
prions
infectious protein particles that lack nucleic acids and replicate by coverting similar, normal proteins into new prions, cause diseases such as spongiform encephalopathies
spongiform encephalopathies
disease caused by prion aggregates that cause nervous degradation. known as Creutzfeld-Jacobs Disease, Mad Cow, Scrapie
Which of the following is not an ancellular agent?
a. viroid
b. virus
c. rickettsia
d. prioin
c. rickettsia
Which of the following statements is true?
a. viruses move toward their cell hosts
b. viruses are capable of metabolism
c. viruses lack a cell membrane
d. viruses grow in response to their environmental conditions
c. viruses lack a cell membrane
A virus that is specific for a bacterial host is called a
a. phage
b. prion
c. virion
d. viroid
a. phage
A naked virus
a. has no membranous envelope
has injected its DNA or RNA into a host cell
is devoid of capsomeres
is one that is unattached to a host cell
a. has no membranous envelope
Which of the following statements is false?
a. viruses may have circular DNA
b. dsRNA is found in bacteria more often than in viruses
c. viral DNA may be linear
d. typically, viruses have DNA or RNA, but not both
b. dsRNA is found in bacteria more often than in viruses
When a eukaryotic cell is infected with an enveloped virus and sheds viruses slowly over time, this infection is
a. called a lytic infection
b. a prophage cycle
c. called a persistent infection
d. caused by a quiescent virus
c. called a persistent infection
Another name for a complete virus is
a. virion
b. viroid
c. prion
d. capsid
a. virion
Which of the following viruses can be latent?
a. HIV
b. chickenpox virus
c. herpesviruses
d. all of the above
d. all of the above
Which of the following is not a criterion for specific family classification of viruses?
a. the type of nucleic acid present
b. envelope structure
c. capside type
d. lipid composition
d. lipid composition
A clear zone of phage infection in a bacterial lawn is
a. a prophage
b. a plaque
c. naked
d. a capsomere
b. a plaque
uncoating
the removal of a viral capsid within a host cell
prophage
an inactive bacteriophage, which is inserted into the host's chromosome
retrovirus
any +ssRNA virus that uses the enzyme reserve transcriptase carried within its capsid to transcribe DNA from its RNA (ex-HIV)
bacteriophage
virus that infects and usually destroys bacterial cells
capsid
a protein coat surrounding the nucleic acid core of a virion
envelope
membrane surrounding the viral capsid
virion
a virus outside of a cell, consisting of a proteinaceous capsid surrounding a nucleic acid core
provirus
inactive virus in an animal cell
benign tumor
mass of tumor cells that remains in one place and is not generally harmful
bacteriophage cycle
1. attachment
2. entry
3. synthesis
4. assembly
5. release
5 phases of a generalized lytic replication cycle
1. Attachment of the virion to the host cell.
2. Entry of the virion into the host cell
3. Synthesis of new nucleic acids and viral proteins by the host cell's enzymes and ribosomes.
4. Assembly of new virions within the host cell.
5. Release of the new virons from the host cell.
Why is it difficult to treat viral infections?
Viruses live inside the body's cells and take control of the cell's metabolsim. They are "protected" from medicines, which usually move through the bloodstream. Antibiotics do not work for viral infections. There are a few antiviral medicines available.
Describe 3 different ways that viral nucleic acid can enter a host cell.
Direct penetration, membrane fusion, endocytosis
Contrast lysis and budding as a means of release of virions from a host cell.
Viruses can be released from the host cell by lysis, a process that kills the cell by bursting its membrane and cell wall if present. Enveloped viruses (e.g., HIV) typically are released from the host cell by budding. During this process the virus acquires its envelope, which is a modified piece of the host's plasma or other, internal membrane.
What is the difference between a virion and a virus particle?
A virion is a virus outside of a cell, Virus particles resemble viruses, but are non-infectious because they do not contain any viral genetic material
How is a provirus like a prophage? How is it different?
A provirus is an inactive virus in an animal cell. A prophage is an inactive bacteriophage which is inserted into a host's chromosome. They are both latent but some proviruses do not become incorporated into the chromosomes of their hosts cells and phages always do. Also some animal viruses like HIV do become part of the host chromosome as a provirus and they are a permanent, physical part of the te host's chromosome, and all descendants of the infected cell will carry the provirus.
Describe lysogeny.
a dormant viral infection of bacteria in which the genetic material of a virus combines with that of a host bacterium
How are viruses specific for their host's cells?
Viruses have proteins on their capsule that bind preferentially to certain receptors on cells. This is why viruses can selective bind certain types of cells. For example, HIV has a protein on its surface that is specific for receptor proteins on immune cells. This is why HIV selectively infects and attacks the immune system.
Compare and contrast diploid cell culture and continuous call culture.
Diploid cell cultures are created from embryonic animal, plant or human cells and last no more than 100 generations. Continuous cell cultures last longer because they are derived from tumor cells and can last indefinitely.