AuCoin I: Viral Classification Flashcards
Viruses are (blank) agents.
filterable
**can pass through a filter
Viruses are obligate intracellular parasites. What does this mean?
viruses can’t make energy or proteins independently of a host cell
Are viral genomes DNA or RNA?
may be either, but not both
Viruses have a (blank) or an envelope morphology
naked capsid
Are viruses living? What must they do to endure in nature? How do viruses infect humans and other hosts?
no; they must be infectious; mutation and selection
Viruses can enter a cell, but they must be able to use (blank) to produce their components. Viruses must encode any required processes not provided by the cell.
host cell processes
ex: use transcription factors from the host cell
Components of a virion? What can happen to naked capsids?
DNA or RNA
structural proteins
enzymes + nucleic acid binding proteins
these form a nucleocapsid or a naked capsid
nucleocapsids may gain glycoproteins and a membrane and become an ENVELOPED virus
What are some examples of naked capsid viruses or unenveloped viruses?
papilloma virus
adenovirus
poliovirus
What are some examples of enveloped viruses?
herpesvirus
retroviruses
What are some means of classifying viruses?
structure - size, morphology, nucleic acid
biochemical characteristics - structure/mode of replication
disease - what do they cause
means of transmission - arbovirus = spread by insect
tissue or organ
What is an arbovirus?
virus spread by insects
What is a RETROvirus?
synthesized DNA from RNA
Are there more DNA viruses or RNA viruses?
RNA viruses
Can + sense RNA cause infection? Can - sense?
yes - it is like messenger RNA and will infect a host cell; negative sense will not infect a host cell
Viruses are measured in (blank)
nanometers
What is the largest virus that can be seen under a light microscope?
poxviruses
Why are some viruses large vs small?
larger viruses hold larger genomes and are more complex
Describe the structure of a virion. What can be found between the capsid and the envelope?
virion = nucleic acid genome packaged into a protein coat (capsid) or within a larger membrane (envelope); in between the capsid and the envelope, you may find a tegument layer packed with viral proteins
Target cells for viruses have receptor proteins. How do viruses bind to their target?
viral attachment proteins are located on the surface of the capsid or envelope - these mediate the interaction of the virus and target cell
Antibodies that bind viral attachment proteins on the virus and block infection are (blank) antibodies
neutralizing
The capsid is a rigid structure. This makes viruses with naked capsids resitant to (blank)
drying, acid, and detergents
How can naked capsid viruses be transmitted?
fecal oral route or in sewage
What does the viral envelope contain?
lipids, proteins, and glycoproteins
Viral envelops are maintained only in aqueous solutions. So, how are they transmitted?
in body fluids
Capsids can be (blank): self assemble on the RNA gemone and form a (blank)
helical (rod); ribonucleocapsid
Helical capsids are found within what type of viruses?
found within most negative-strand RNA viruses
Capsids can be (blank), which take the form of a sphere that is assembled from symmetrical subunits.
Simple icosahedrons like picornaviruses are made of 12 (blank) each with fivefold symmetry (pentamer)
icosahedrons; capsomers
What are viral envelopes composed of?
lipids, proteins, glycoproteins - formed from cellular membranes
Most (blank) on viruses act as VAPs that bind to target cells to initiate entry. VAPs that bind to red blood cells are (blank)
glycoproteins; hemagglutinins
The glycoproteins on the viral envelop can form (blank) that are usually immunodominant.
spikes
**these cause an immune response
All of the negative strand RNA viruses have this
an envelope
(blank) is situated between the envelope and nucleocapsid - contains enzymes, and other proteins that facilitate viral infection. (Herpesviruses)
tegument layer
Does the host cell assist the virus in replication?
yes; the host cell provides substrates, energy, and some of the machinery necessary for viral replication
What are the phases of viral replication?
- virus recognizes its target cell via VAPs
- it attaches and penetrates the plasma membrane
- it uncoats its genome into the cytoplasm and delivers the genome to the nucleus
- viral genome replicates and transcription occurs to produce necessary proteins
- virus assembles and is released via lysis or like the secretory pathway in vesicles?
Which cells a virus infects are dependent on its VAPs. VAPs are usually specific (blank) of enveloped viruses. Viruses may bind to receptors on cell types of (blank) only
glycoproteins; specific species
The cell that is susceptible to viral binding defines the tissue (blank)
tropisms
The HA of influenza A virus binds to (blank) expressed on many different cells and has a (blank) host range and tissue tropism
sialic acid receptors; broad
How do most nonenveloped viruses enter the host cell?
receptor mediated endocytosis
How do enveloped viruses deliver the nucleocapsid or genome into the cytoplasm of the host cell?
by fusing its membrane
T/F: Fusion proteins may be active at neutral pH or may need acidic conditions of an endosome to fuse
true
Where are most DNA genomes delivered in the host cell? What about RNA genomes?
to the nucleus; RNA genomes remain in the cytoplasm
Most DNA viruses use the cells (blank) and other enzymes to make mRNA; mRNA must acquire what two components?
DNA-dependent hose RNA polymerase II; 3’ poly A tail and 5’ methylated cap
Most RNA viruses replicate and produce (blank) in the cytoplasm. Therefore, the virus must encode the (blank) for transcription
mRNA; enzymes
What types of viruses replicate in the nucleus?
DNA viruses - retroviruses and influenza
Some complex DNA viruses encode their own (blank) to regulate the expression of viral genes. Viral DNA replication begins at the (blank). Viral replication factors bind to this region.
trx factors; origin
Viruses with large DNA can encode their own (blank) which makes room for errors and mutations - these polymerases can be the target of (blank)
DNA polymerase; antiviral nucleotide analogs
Describe the process of DNA viral replication
- attachment and penetration of host cell via fusion
- moves to the nucleus
- immediate early protein synthesis – trx factors
- early protein synthesis and genome replication
- late protein synthesis
- DNA containing naked capsids enter ER, gain mature glycoproteins and become mature enveloped virions
- exocytosis and release of mature virions
RNA virus must encode a (blank). These polymerases are fast and have a high (blank)
RNA-dependent RNA polymerase; mutation rate
The (blank) RNA viral genomes act as mRNA, bind to ribosomes, and direct protein synthesis
Therefore, this (blank) viral RNA alone can initiate infection
RNA-dependent RNA polymerase will produce a (blank) RNA template that can be used to produce more (blank) RNA
+ strand; + strand; - strand; + strand
What is the template for production of + mRNA?
- strand mRNA
**NOT INFECTIOUS
Where does RNA viral transcription and replication occur?
in the cytoplasm, except for influenza viruses
What does the 5’ cap structure of viral mRNA do?
mediates binding of viral mRNA to host ribosomes
(blank) bind to viral mRNA and may produce one large polyprotein which needs to be cleaved by cellular or viral proteases
Viral mRNA is preferentially translated in many cases. Some viruses block cellular mRNA egress from the (blank)
Some viral proteins require post-translational modifications such as (blank)
Viral glycoproteins are synthesized on membrane-bound (blank) and have the amino acid sequences to allow for (i) insertion into the rough endoplasmic reticulum and (ii) N-linked glycosylation
ribosomes; nucleus; phosphorylation and glycosylation; ribosomes
When the concentration of viral structural components is high enough in the cell then protein-protein, protein-nucleic acid, and protein –membrane interactions occur
Viral (blank) occurs after association of the nucleocapsid with the intracellular portion of viral glycoproteins
Most RNA viruses bud from the (blank)
Other viruses acquire their envelope by budding into the (blank)
budding; plasma membrane; Er and golgi
What are some ways viruses can be released?
cell lysis
exocytosis
budding from the plasma membrane
What is the difference in lethal mutations vs attenuated mutations?
attenuated mutations cause less severe disease
In what ways can viruses undergo mutation?
new strains are produced by recombination or segmented genomes can shuffle their segments
Can the + strand viral RNA alone initiate infection? Can the - strand viral RNA initiate infection?
yes; no, not unless the polymerase is present
What provides the template to produce more + strand RNA?
- strand RNA
