Microbiology Chapter 13
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.
bacteriophage cycle
1. attachment 2. entry 3. synthesis 4. assembly 5. release
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.
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
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.
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.
Describe 3 different ways that viral nucleic acid can enter a host cell.
Direct penetration, membrane fusion, endocytosis
neoplastic cells
Tumor (abnormal function, unregulated growth "steals nutrients from other tissues")
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.
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.
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.
virion
a complete viral article, including a nucleic acid and a capsid, outside of a cell
Describe lysogeny.
a dormant viral infection of bacteria in which the genetic material of a virus combines with that of a host bacterium
capsid
a protein coat surrounding the nucleic acid core of a virion
virion
a virus outside of a cell, consisting of a proteinaceous capsid surrounding a nucleic acid core
bacteriophage
a virus that infects a bacterial cell
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
A virus that is specific for a bacterial host is called a a. phage b. prion c. virion d. viroid
a. phage
Another name for a complete virus is a. virion b. viroid c. prion d. capsid
a. virion
prophage
an inactive bacteriophage, which is inserted into the host's chromosome
latency
animal virus remains inactive in a cell as part of a chromosome or in the cytosol
retrovirus
any +ssRNA virus that uses the enzyme reserve transcriptase carried within its capsid to transcribe DNA from its RNA (ex-HIV)
5 stages of the replication cycle of a virus
attachment, entry, synthesis, assembly, release
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
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
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
plaques on the bacterial lawn
clear areas on a agar plate where bacteria has been infected with phages lyse
negative-strand RNA
complementary to mRNA, genome must be transcribed by viral RNA polymerase to produce viral RNA
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
continuous cell cultures
derived from cancer cells, last longer than diploid cell cutures
2 types of cell cultures on which viruses can be grown
diploid cell cultures and continuous cell cultures
spongiform encephalopathies
disease caused by prion aggregates that cause nervous degradation. known as Creutzfeld-Jacobs Disease, Mad Cow, Scrapie
ssRNA virus
has positive-strand RNA which can be directly translated by ribosomes to synthesize protein
dsDNA virus
in a virus, acts like cellular DNA in transcription and replication
provirus
inactive virus in an animal cell
prions
infectious protein particles that lack nucleic acids and replicate by coverting similar, normal proteins into new prions, cause diseases such as spongiform encephalopathies
How are viruses cultured in a lab? Why?
inside mature organisms or embryonated chicken eggs, because viruses cannot metabolize or replicate alone
common characteristics of viruses, viroids, and prions
lack cell structure cannot metabolize, grow or self-produce cannot respond to the environment
diploid cell cuture
last 100 generations
tumor
mass of neoplastic cells
benign tumor
mass of tumor cells that remains in one place and is not generally harmful
envelope
membrane surrounding the viral capsid
uncoating
process by which the capsid is removed after the virion enters the cell
capsomeres
protein subunits of capsids that surround viruses
Viruses depend on _________________.
random contact with a specific host cell type for replication
positive-strand RNA
same polarity as MRNA so genome RNA can be translated in cytoplasm by host cell ribosomes
viroids
small circular pieces of RNA with no capsid that infect and cause disease in plants
capsid
the coating of protein surrounding the nucleic acid of a virus
uncoating
the removal of a viral capsid within a host cell
provirus
the viral DNA which inserts into a host cell's chromosome
virus
tiny infectious agent with nucleic acid surrounded by capsomeres
lyse
to burst
How are viruses classified?
type of nucleic acid, presense of an envelope, shape, size
neoplasia
uncontrolled cell reproduction in a multicellular animal
bacteriophage
virus that infects and usually destroys bacterial cells
phages
viruses that infect bacteria
oncogenic virus
viruses that lead to cancer by permanently altering its genetic material
