Classification, Structure, and Replication of Viruses - AuCoin Flashcards
T/F: viruses can pass through a filter
true
Viruses are obligate (blank)
intracellular parasties
T/F: viruses can make energy and proteins independent of a host cell
false
What are the limitations of the viral genome?
it can be DNA or RNA BUT NOT BOTH
What are the two general viral morphologies?
naked capsid or enveloped
What two processes have optimized viruses to infect humans and other hosts?
mutation and selection
What is a important characteristic of the genes a virus encodes to ensure its survival?
it must code for any process not provided by the host cell and its components MUST SELF ASSEMBLE
What types of cellular components do viruses hijack?
polymerases and transcription factors
structural proteins and enzymes and nucleic acid binding proteins all together form the (blank)
nucleocapsid
A nucleocapside and a glycoprotein and a membrane make a (blank)
enveloped virus
Papilloma virus, adenovirus, and polio viruses are all (blank) viruses
naked capsid viruses
herpesvirus and retrovirus are both (blank) viruses
enveloped viruses
Hepatitis A virus is a (blank) virus, while all other hepatitis viruses are RNA viruses
DNA
What are the means of classifying viruses?
- structure: size, morph, and nucleic acid
- BCH characteristics like structure and mode of rep
- disease (encephalitis)
- means of transmission
- tissue or organ affected
what is viral tropism?
when a virus preferentially targets a specific tissue type
Picornavirus is a example of (blank) naming
structural
Retroviruses is an example of (blank) naming
BCH
adenoviruses and reoviruses are examples of (blank) naming
tropism
Pox, herpes, and hepadna viruses are all (blank) DNA viruses
enveloped
Polyoma, papilloma, adeno, and parvo viruses are all (blank) DNA viruses
enveloped
Parvovirus is special because it is (ds/ss) DNA
ssDNA
+ RNA is equal to (blank)RNA
mRNA
What is the unit of measurement for viruses? How do they compare to the size of staph?
nanometers, 1/4 the size
T/F: larger virions hold larger genomes and are therefore more complex
true
What is a virion?
infectious particle made of nucleic acid genome packaged into a protein coat or membrane
Where are viral proteins packaged within the virion?
in the tegument layer, between the capsid and envelope
What is the size of poxvirus? E. coli? Human cell?
Poxvirus: 0.3um
E. Coli: 6.0um
Human cell: 30-100 um
What is the shape of the nucleocapsid in nake viruses?
icosahedral
What are the two shapes of the nucleocapsid in enveloped viruses?
icosahedral or helcial ribonucelocapsid
What makes up a ribonucleocapsid?
Protein and RNA together
The (blank) on the surface of the capsid envelope mediates the interaction of the virus and target cell
viral attachment protein
Neutralizing Abs bind to (blank) and block infection
viral attachment proteins
T/F: the capsid is a fluid structure
false
Viruses with (capsid/membrane) are resistant to drying, acid, and detergents
capsids
(Naked/enveloped) viruses can be transmitted via fecal oral or via sewage
naked
The viral envelope contains lipids, proteins, and glyco(proteins/lipids)
glycoproteins
Since the envelope is only maintained in aqueous solution, enveloped viruses are only transmitted via (blank)
body fluids
gp120 protein on HIV binding CD4 on Tcells is an example of the (blank) protein
viral attachment protein
An (icosahedral/ribonucelocapsid) is found in most negative strand RNA viruses
helical ribonucleocapsid
T/F: the helical ribonucleocapsid can self assemble
true
Vesicular stomatitis virus nucleocapsid is a good example of the (blank) structure
helical ribonucleocapsid
What two protein subunits make of the ribonucleocapsid?
N and M
The icosahedron of picornavirus, which is simple, is made of 12 (blanks) with five fold symmetry (i.e. a pentamer)
capsomers
Five protomers come together to form one (blank)
capsomer
How does something like herpesvirus create a more complex capsid?
by inserting structurally distinct proteins between the pentamers (capsomers)
what material is hijacked to make the building blocks of the viral envelope
cellular membrane
most (blanks) act as viral attachment proteins that bind to target cells to initiate entry
glycoproteins
VAPs that bind to RBCs are called (blank)
hemagglutinins
What are the spikes on viruses?
glycoproteins
T/F: cellular proteins are often found in viral membranes
false
T/F: the glycoprotein spikes on viruses are usually immunodominant
true
T/F: all negative strand RNA viruses are enveloped
treu
What is interesting about the influenza A genome?
it is segmented -RNA
The (blank) layer is betweent he envelope and nucleocapsid and contains enzymes and other proteins that facilitate viral infection
tegument
what are the processes involved in viral replication?
recognition attachment penetration uncoating delivery of genome to nucleus
Genome replication and macromolecular synth is followed by viral (blank) and release
assembly
(blank) is when extracellular infectious virus is not detected but viral genomes can be detected
latency
latency is a hallmark of what type of infection?
herpesvirus
T/F: viral protein synth and genome replication happen at the same time
true
what determines what cells can be infected by a virus?
binding of the VAP to the cell receptors
T/F: VAPs can be proteins, CHOs, glyocproteins, or glycolipids
true
what is a viral host range?
viruses can enter only the cells that express the right receptor type
What macromolecule are VAPs normally?
glycoproteins
The HA VAP of influenza A binds to the (blank) receptor of a broad range of cell types
sialic acid receptor
What type of macromolecule is HA?
glycoprotein
Most nonenveloped viruses enter the cell via (blank)
receptor mediated endocytosis
T/F: enveloped viruses fuse their membrane with the cell membrane to inject the nucleocapsid into the cytosol
true
at what pH are fusion proteins active?
neutral OR acidic conditions of the endosome following receptor mediated endocytosis
Where are DNA genomes delivered?
nucleus
Where are RNA genomes delivered?
cytoplasm
T/F: both the envelope and the capsid must be removed to begin replication
true
Which DNA virus does not have its DNA moved to the nucleus?
Pox virus
What RNA pol does the virus use to make mRNA?
RNA Pol II
what mods does viral mRNA get?
3’ poly A tail and 5’ methylated cap
T/F: viruses encode the enzymes for transcription RNA dependent RNA Pol
true
What is the function of the poly A tail?
nuclear export and mRNA stability
What is the function of the 5’ 7-methyl-guanosine cap?
binds to the ribosomes
RNA retroviruses and orthomyxovirus like influenza replicate where
in the nucleus!
T/F: replication of viral DNA is semiconservative
true
T/F: replication of viral DNA can be rolling circle or linear
true
Describe dsDNA viral rep?
dsDNA to mRNA to protein
Describe ssDNA viral rep?
ssDNA to dsDNA to mNRA to protein
Describe segmented dsRNA viral rep?
segmented dsRNA makes mRNA from each segment
What is the difference between the requisites at the time of infection between + and -RNA viruses?
-RNA needs to have a synthesized protein RNA dep. RNA pol to initiate its own transcription while +RNA can code for it and the cell’s ribosomes will make it for it
What happens during +RNA viral translation?
one large polyprotein is made and is cleaved by either viral or host enzymes
How are +RNA viruses replicated?
Host ribosome makes all the proteins from +RNA genome. RNA dep. RNA Pol from RNA genome makes -RNA template, from which it makes multiple +RNA genome copies for packaging
T/F: retroviruses are integrated into the host genome
true
T/F: DNA viruses are larger than RNA viruses
true
some complex DNA viruses can encode their own (blank) to regulate expression of viral genes
transcription factors
Viral DNA replication begins at the (blank), where viral replication factors bind, such as DNA dep DNA Pol
Ori
Large DNA viruses encode their own DNA Pol which will make more (blanks) creating mutations
errors
Antiviral nucleotide analogs target what?
viral polymerases
immediate early genes code for:
transcription factors
early genes code for:
protein synthesis and genome replication
late genes code for:
structural proteins; glycoproteins, capsid proteins, and tegument proteins
What two types of genes produce products that go back into the nucleus?
immediate early and early genes
the signal sequence in viral mRNA will signal it to attach to ribosomes located on the (blank0
rER
what types of modifications will the protein made in the rER undergo?
glycosylation and acetylation
What is the fate of the cytoplasmically created structural proteins?
They go back into the nucleus to make the capsid.
Where does the DNA containing naked capsid immediately go after exiting the necleus?
rER
Where does the capsid gain its envelope?
trans golgi
(blank) proteins will bind to the intracellular portion of the glycoprotein coat to link it to the capsid
tegument
Proteins involved in cell take over are expressed in what genes?
IE
DNA dep DNA pol is expressedin what type of genes?
early
T/F: the genome is replicated during the transcription of the late genes
false; BEFORE
What are the two methods that the virus is released from the cell?
exocytosis or cell lysis
RNA viruses must code for what type of Pol?
RNA dep RNA pol
What is unique about RNA dep RNA pol regarding virulence?
they are fast and have a high mutation rate
T/F: viral +RNA ALONE can initiate infection
true
T/F: viral -RNA ALONE can initiate infection
false
except for influenza, RNA viral transcription and replication occurs in the (blank)
cytoplasm
describe the fidelity of RNA dep RNA pol?
LOW FIDELITY
T/F: RNA dep RNA pol has the ability to proofread
false, that’s why its low fidelity
RNA dep RNA pol have a mutation rate of (blank) while DNA dep DNA pol has a mutation rate of (blank)
1:3000 vs 1: billion
rhabdovirus is shaped like a (blank)
bullet
L and NS proteins come together to form (blank)
RNA dep RNA pol
What is the G protein, where is it modified, and how is it modified?
the surface glycoprotein, GLYCOSYLATED (for G) in the rER
Where does the G protein go?
embeds in the plasma membrane to await viral nucelocapsid
Discuss the formation of the envelope-nucleocapsid
matrix protein associates with the intracellular portion of G protein; nucleocapsid assembles and N protein also associates with the M protein intermediate.
what three proteins make up the nucleocapsid?
N, L, and NS
Does host or viral mRNA have translational priority?
viral mRNA
T/F: viral mRNA can block host mRNA egress from nucleus
true, they can also degrade host mRNA
What two amino acid sequence determined actions are necessary fro viral glycoproteins?
insertion into the rER and N-linked glycosylatoin
Addition of sugar molecules to the nitrogen atom of asparagine (N) linked is an example of what type of mod?
N-linked glycosylation
How are protease inhibitors used as antivirals?
they block the cleavage of polyproteins into individual functioning proteins
Are protease inhibitors effective against segmented genomes?
NO, they make one-gene-one-protein style translation, so no polyprotein
T/F: viral membranes contain host proteins since they got their membrane from the plasma membrane
false!
When the concentration of viral proteins is sufficiently high, what three types of protein-(blank) interactions occur>?
protein-nucleic acid
protein-protein
protein-membrane
(blank) only occurs after the association of the nucleocapsid with the intracellular portion of G protein
budding
Where do most RNA viruses bud?
from the plasma membrane
besides the PM, where else can viruses bud from?
ER or the golgi
what are the three methods that a virus can be released from a cell?
cell lysis, exocytosis, or budding from the plasma membrane
Naked capsid viruses take what route of cell exit?
lysis–the membrane is broken so you can’t use it to form an envelope
What is the only step in viral capsid assembly that requires ATP?
insertion of the genome into the capsid
What two proteins can the G protein bind to?
the M protein or directly to the riboproteins on the RNA
T/F: mutated viruses by definition change the phenotype, are more detrimental, and enhance pathogenicity and drug resistance
false; just means that they’re different that wild type
what happens if you have a mutation in an essential gene?
it is lethal to the virus
attenuated mutants cause (more/less) disease
less
New virus STRAINS can be produced by intermolecular exchange (aka blank) between viruses OR VIRUS AND THE HOST
recombination
What is viral reassortment?
when a segmented viral genome shuffles its segments if more than one viral strain is present in the host cell
the ideal host is a (blank) host
naive
100nm is how many angstroms?
10A