Micro2. Chaps 14
Terms
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- Animal viruses have an _____ or _____ genome that is either double or single stranded.
- DNA or RNA
- Animal viruses are surrounded by a protein coat called a _______.
- Capsid
- The nucleic acid and the capsid are called __________.
- Nucleocapsid
- Some viruses have an ________ which acts as a phospholipid bilayer membrane that was obtained from the cell in which the virus arose.
- Envelope
- Viruses are _________ intracellular ___________.
- Obligate intracellular parasites.
-
Viral genomes vary. Define:
Polioviruses
Herpeviruses
Retroviruses
Influenza viruses -
Poliovirus = ss RNA
Herpevirus = ds DNA
Retrovirus = Diploid ss RNA
Influenza Virus = multiple gene segments of ss RNA - What is the simplist genome and largest genomes of animal viruses?
-
Hantavirus = simplist = 3 genes that encode 4 polypeptides
Pox virus = most complicated = 200 genes - What is the nomenclature rule for viruses?
- Viruses are names for the geographic region in which they are discovered.
- What are the three things that are used to classify viruses?
-
1. Genome structure
2. Virus particle structure
3. Presence or absence of an envelope - Viruses are grouped based on their __________ _________.
- Transmission mechanism
- What are the four groupings of transmission mechanisms?
-
1. Enteric viruses (fecal-oral route)
2. Respiratory viruses (aerosols)
3. Zoonotic agents (biting or resp. route)
4. Sexually-tranmitted - Viruses tend to be species and cell ________.
- Specific
- Step 1 of infection is called __________.
- Attachement
- Attachement is mediated by ____-_______ molecule(s) and viral ______ _______.
-
Cell-surface
spike proteins - HIV gp120 is specific for CD4, which are principally found on ________ ____ cells.
- Helper T cells
- Attachement occurs by _________ interactions.
- Noncovalent
- Some viruses ______ with a cell's plasma membrane. HIV's gp___ interacts with a cellular __________ receptor to induce fusion.
-
Fuse
gp41
chemokine - In both fusion and endocytosis, the ________, containing the nucleic acid and viral enzymes, is ________ into the _________.
-
Capsid
dumped
cytoplasm - Most DNA viruses replicate in the __________, while most RNA viruses replicate in the __________.
-
DNA = Nucleus
RNA = Cytoplasm - Some viruses ________ their dsDNA into the host cell's genome. Some viruses copy their RNA into ______, which is then integrated into the host cell's genome.
-
Integrate
dsDNA - Uncoating is caused by the dissociation of the _______ _______ from the ________ subunits that make up the capsid. This causes the capsid to ___________ and liberates the nucleic acid.
-
Nucleic Acids
Protein subunits
Disintegrate - Some RNA virus genomes act as a mRNA, these are termed:
- plus-strand viruses
- If a virus is not a plus-strand it has a prepackaged, _____-encoded ____-dependant RNA pol and is termed a ______-strand virus.
-
virus-encoded
RNA-dependant
Minus-strand - DNA viruses encode ____ polymerases.
- RNA
- Many viruses have ______cistronic mRNA's.
- Polycistronic
- Step 6 of infection is:
- Maturation
- Maturation of a virus in a cell involves the ________ of polycistronic polypeptides into ________.
-
Cleavage
Subunits - Nucleic acids and capsid proteins spontaneously __________ into ___________.
-
Polymerize
Nucleocapsid - HIV gp____ polypeoptide is cleaved into its gp____ and gp___ mature polypeptides. This step is inhibited by the ____ ________ __________ taken by HIV+ people.
-
gp160 --> gp120 and gp41
HIV protease inhibitors - Step 7 of infection is:
- Release from cells
- Some viruses rely upon _____ ______ for release into the extracellular matrix. This is like a balloon being blown up till it pops.
- Cell lysis
- Other viruses rely upon ________, whereby they exit from the cell, taking some of its membrane. These viruses don't exceed the capacity of the cell.
- Budding
- Budding occurs in one of three places depending on the viral species, these locations are:
- The plasma membrane, the Golgi or the ER
- Step 8 of viral infection is:
- Shedding from the host
- __________ ________ ________ would be an example of a catastrophic shedding event, while a ______ _____ is an example of a minor shedding event.
-
Hemorrhagic fever virus
Common cold virus - Step 9 of infection is:
- Trasmission to other hosts
- Transmission routes usually reflect the ______ of _________ for viruses.
- Site of infection
- List the 3 types of persistant infections:
-
1. Latent
2. Chronic
3. Slow - Hepatitis ___ is the greatest current health risk.
- C
- __________ ________ refers to even if you get vaccinated, if you're exposed heavily, you can still get the virus.
- Vaccine breakthru
- List the 3 mechanisms that account for viruses driving cell proliferation:
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1. Oncogenes stimulate cell proliferation
2. Viral DNA integrates adjacent to genes that drive cell division
3. Some viruses encode growth factors - Epstein-Barr virus encodes the growth factor _______ __________-10 that causes ___ cell proliferation, leading to ________ ___________.
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Viral interleukin-10
B cell
Burkitt's lymphoma - Influenze A viruses have ___ gene segments that encode 10 polypepetides. Segment __ and ___ are prominant in causing outbreaks
-
8
Segments 6 and 4 - Latent infections
-
-Periods of inactivation and activation
-Usually limited pathology
-Herpes viruses - Chronic infections
-
Infectious virus can be detected for years or decades with little discernable pathology but can eventually lead to disease
-Hep B and C viruses - Slow infections
-
-Short period of acute infection followed by apparent disappearance of virus for months or years with pathology ensuing
-HIV - Tumor viruses drive cell ________ so they can have more homes.
- proliferation
- _________ viruses, like influenza, contain multiple genetic elements that encode different genes.
- Segmented
- ________ of a cell with two or more different strains of a virus can lead to the emergence of __________ viruses that have distinct characteristics. This is called ___________.
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Coinfection
Reassortant viruses
Reassortment - The H5N1 influenza virus has subtype __ ____ segment and subtype __ ____ segment.
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5 HA
1 NA - What are the two main methods used to study viruses?
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1. Cultivation of host cells
2. Cell culture - Cultivation of host cells involves __________ chicken eggs that must be _________ to the virus.
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Embryonated
Suseptible - The two main targets in cultivation of host cells are:
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1. Chorioallantoic fluid (CAF)
2. Embryo - Step 2 of infection is:
- Entry into the cell
- Other viruses are internalized by _________.
- endocytosis
-
Step 3 is:
Step 4 is: -
Targeting to the site of replication
Uncoating
(these steps go together) - Step 5 of infection is:
- Nucleic acid replication and protein synthesis
- In a cell culture, cells are grown attached to flasks in a ________, inoculated with the virus and within days, ________(CPE) effect can be seen.
-
Monolayer
Cytopathic effect -
Prions are...
Prions cause... -
-Proteinaceous infectious particles
-spongiform encephalopathies - Prions contain no _______ acids. They are a normal cellular protein that has ________ into a ________ protein.
-
Nucleic
Misfolded
Pathogenic - List 3 diseases caused by prions;
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1. Creutzfeldt-Jakob (from mad cows)
2. Kuru (religious consumption of brains of deceased)
3. Chronic wasting disease (deer, elk, moose)