how do viruses replicate
by assembly of subunits in infected cells
What are the steps for viral replication
- attachement
- penetration
- uncoating
- early transcription
- early translation
- replication
- late transcription
- late translation
- assembly
- release
What are the two ways that viruses can kill
causing an overactive immune system (angry macrophages)
inhibiting the immune system
what is the primary example of a virus that kills by causing an over active immune system
influenza
what is the primary example of a virus that kills bu inactivating the immune system
Ebloa (also HIV)
What is the main difference between positive and negative RNA virus replication
a positive strand is just like mRNA so it is immediately translated, negative strand mRNA has have a complementary strand made, then have that one translated
although positive and negative RNA virus replication is different, what is one important similarity
they both create double stranded RNA
why is double stranded RNA so important
it is the signal that induces the synthesis of interferon
can viruses resist interferon action
yes
what is a retrovirus
an RNA virus that goes from RNA to double stranded DNA.
what is needed by a retrovirus, and can be the target of antiviral drugs
RT
What is the main target of antibodies against viruses
antibodies against particles on the viral envelope, this prevents them from binding to the cell
What are the different outcomes of a viral infection for the cell
- Abortive infection
- Latent infection (can become a productive infection)
- productive infection (can lead to cell death or a persistent infection)
- apoptosis
What are the four immune mechanisms that fight viruses and what do they cause
- interferon - blocks infection, kills infected cells
- NK cells - kill infected cells
- B cells/antibody - neutralizes viruses, enhance phagocytosis
- Cytotoxic T-cells - kills infected cells
What are the TLRs that are important to antiviral activity
TLR 3, 7, 8, and 9
What does TLR3 recognize and result in
TLR 3 recognizes DsRNA and produces IFN-beta
what do TLR 7, and 8 recognize and result in
they recognize viral ssRNAand produce IFN-1 alpha
What does TLR 9 recognize and result in
it recognizes unmethylated CpG, and results in IFN-alpha
what type of cell produces the most IFN-alpha
plasmacytoid dendritic cells
what is the sequence of events from TLR recognition to IFN production
- TLR recognition
- signal pathway
- transcription factors
- Interferon production
- Release of interferon
- protection of non-infected cells
What is type 1 interferon
IFN alpha and beta
produced by immune cells and infected cells
what is type 2 interferon
antiviral and defense against intracellular bacteria and parasites
produced by immune cells only
What are the three ways in which interferons work
- they inhibit all translation (type 2 IFN only does this)
- they degrade mRNA and rRNA
- they inhibit transcription, and viral assembly
(type 1 IFN does all three)
What does STAT do?
it causes IFN to be produced
how can viruses evade antiviral defenses
- Influenza NS1 binds to dsRNA
- Ebola prevents dsRNA from inducing IFN release
- Ebola inhibits RNA silencing
- adenovirus blocks STAT1 from functioning
- Vaccinia prevents IFN from attaching
What are the two ways that a virus can initiate apoptosis
extrinsic (death by instruction)
intrinsic (death by stress)
how is apoptosis carried out
activation of caspases, which basically chew everything in the cell up, then they are and ingested by phagocytes
is apoptosis good or bad for the virus inside the cell
it can be both. Some viruses initiate apoptosis, others prevent it so the cell will stay live and produce more virus
What is a latent viral infection
the viral genome is present, but there are no infectious viral particles
What is lysogeny
when a viral genome integrates into the host genome
what is an episomal viral genome
when a viral genome isn’t entered into the host chromosome (like a bacterial plasmid)
which viruses cause chronic inflammation
Hep B and C
which viruses can cause cancer
Hep B and C
what is a viral oncogene
cancer causing genes in sarcoma and leukemia viruses
What is tropism
the increased ability of a virus to replicate in certain cells or tissues
what controls tropism
- viral antireceptor
- viral receptor
- route of infection
- transcription factors
- immune system response
What happens to a host with a viral infection
IL-1 - causes fever, somnolence, anorexia, lowers libido, lowers pain threshold
IFN - causes nausea, vomiting, fever, chills, fatigue, malaise, asthenia, myalgia, leukopenia
TNF-alpha - causes inflammation, cachexia, fever, cell lysis
What are acute viral infections
rapid onset, rapid resolution (virus is cleared)(influenza)
what are chronic viral infection
slow onset, slow resolution, cells die, infection spreads (HBV, HIV)
what are persistent infections
virus stay with the host, infected cells live (retroviruses)
what are latent infections
virus stays with the host, reactivation episodes occur (HSV) start and end as acute infections
What is a subclinical viral infection
an infection with no signs or symptoms, but infectious virus is produced and transmittable
What is a virus
a very small non-cellular parasite of cells.
What are the parts of a virus
a DNA or RNA genome
a Capsid (protein coat)
sometimes an envelope
are there parts of our genome that are retroviral sequences
yes, our genome is about 8% retroviral
What is the newest theory on origin of viruses
that viruses preceded cellular organisms
What is a virion
an infectious virus particle
can viruses sustain themselves and replicate
no, they are obligate intracellular parasites (they can’t produce energy or synthesize ribosomes)
What is a capsid
a protective protein shell for the viral genome, composed of capsomers
what are capsomers
the structural components (bricks) of the capsid, they are made of protomers
what are protomers
the building blocks that make up capsomers
What are the functions of viral proteins
- structural
- protect genome
- attachment to host cell
- fusion with cell membrane
- Enzymes
- primers
- immune interference
how are capsids build
they self-assemble, due to reactions with large free energy that proceed to near completion
are all of the components made by viruses for replication used to make new viruses
no, probably not even close, but enough are that the virus still successfully replicates
what is a virion composed of
it is the infectious virus particle, that is composed of RNA or DNA, proteins, and sometimes an envelope
where is the envelope a virus sometimes has obtained from
from a modified cell membrane
What are the two main structures of capsids
helix and icosahedron
what are the functions of the capsid
- protect the genome from nucleases and other hostile things
- necessary for the infectivity of virions
- in naked viruses it serves as the attachment protein
- it is antigenic and invokes an immune response
how many capsid layers do viruses have? any excpetions
1
yes, reoviridae has 3 capsid layers
what is the helical structure of capsids like
it looks like a stack of washers. it is a long tightly coiled protein
What are the shapes that a capsid with helical symmetry can make
sphere
bullet
Rod
thread
What is the capsid of rhabdovirus (rabies) like
helical capsid
tight envelope
bullet shaped
What is the capsid of the influenza virus like
helical capsid
loose envelope
sphere shaped
What is an icosahedra
a structure with
20 equilateral triangles
30 edges
12 verticies
how many axis of symmetry do icosahedra have
3
5 fold
2 fold
3 fold
what is the minimum number of subunits that can make up a face in an octahedron
3
what is the minimum number of subunits a whole icosahedra can have
60 (3 per face x 20 faces)
how do you get larger icosahedra
by adding more subunits per face, not by making larger subunits
What can you have external to the capsid
an envelope (sometimes you do, sometimes you don’t, that depends on the virus)
Which virus has a brick shaped capsid
poxvirus
What are the 4 different types of viral capsids we study
- naked icosahedral
- envelopped icosahedral
- naked helical
- envelopped helical
what are the 4 different types of viral genomes
- single stranded RNA
- double stranded RNA
- single stranded DNA
- double stranded DNA
what shapes do the viral genomes take
circular or linear
what other modifications can viral genomes have
they can be incomplete double stranded
they can be segmented (more than one piece)
What is a positive strand RNA
one that has the same polarity as mRNA (5’-3’)
what is a negative strand RNA
one that has the opposite polarity as mRNA (3’-5’)
What are the three different types of viral DNA genomes
- double stranded with open ends
- double stranded with closed ends
- single stranded
what are the 4 different types of viral RNA genomes
- single stranded +
- single stranded -
- double stranded
- single stranded, segmented
Which strand, positive or negative, ssRNA needs to bring its own RNA dependent RNA polymerase
the negative strand RNA, this way it can make its own complementary copy
How are viruses classified
- DNA or RNA
- Icosahedral or Helical
- Naked or Envelop
- Double Stranded, Single Stranded
- or -
What are the characteristics of the influenza virus (orthomyxo)
- RNA
- Helical
- Enveloped
- Single Stranded (8 SEGMENTS)
- Negative
What are the characteristics of the paramyxo virus
- RNA
- Helical
- Enveloped
- Single Stranded (non-segmented)
- Negative
What are the characteristics of the Filo (ebola) virus
- RNA
- Helical
- Enveloped
- Single Stranded (non-segmented)
- Negative
What are the characteristics of the Corona virus (sore throats)
- RNA
- Helical
- Enveloped
- Single Strand
- Positive
What are the characteristics of the Picorna virus (common cold)
- RNA
- Icosahedral
- Naked
- Single Stranded
- Positive
What should we remember about helical DNA viruses
there are no helical DNA viruses that affect humans
What are the characteristics of the herpes virus
- DNA
- Icosahedral
- Enveloped
- Double Stranded (linear)
What are the characteristics of the hepadna virus (HEP B)
- DNA
- Icosahedral
- Enveloped
- Double Stranded (circular - gapped)
What are the characteristic of the Adeno (upper respiratory) virus
- DNA
- Icosahedral
- Naked
- Double stranded (linear)
What are the characteristics of the Papilloma virus (HPV)
- DNA
- Icosahedral
- Naked
- Double Stranded (circular)
