L31, L33- Viruses Flashcards
individual viral components self-assemble into a….
viron
define viron
complete infectious form of virus outside of host cell
describe the possible viral genomes
- RNA, DNA
- ss, ds
- linear, circular, segmented, haploid, diploid
- neg/pos sense
viral genome is surrounded by (1), made of viral protein subunits, which will create (2)
1- capsomere, capsid
2- nucleocapsid
viruses can be covered by an envelope which originates from (1) and functions to (2); it may also have an additional protein cluster layer termed (3)
1- host cell membrane
2- maintains aqueous soln
3- tegument
a viral capsid is made up of one or more (1)s and are held together by (2)
1- capsomeres (subunits)
2- non-covalent, reversible hydrophobic or H-bonds
list the general forms of nucleocapsid morphology
- icosahedral
- helical
- complex (non-symmetrical)
list the various (4) functions of viral capsid proteins
- define tissue/species specific transmission by interaction with host receptors to facilitate host entry
- interact with viral nucleic acids for packing/assembling virus
- assist in viral/host gene regulation
- evade/block host immune system
describe the components / characteristics of an Isohedral Capsid
- few proteins, 5 protomers form a pentamer
- limited amt of nucleic acids packaged inside
- forms independently from genome
- 5-3-2 axes of symmetry
poliovirus has a ____ capsid
icosahedral capsid
describe the components / characteristics of an Helical Capsid
- rod-like filamentous structure
- capsomeres bind to viral genome (in regular fashion)
- often ‘open-ended’, form around genome (cannot form empty)
- contains RNA genomes
- flexible nucleocapsids wound into ball, surrounded by envelope
rhabdovirus is a _____ capsid
helical capsid
bacterophages have a (1) capsids with the following components: (2)
1- complex symmetry
2- Head (nucleic acid, protein), Tail / contractive sheath, Tail fibers and pins, Base/End plate
viral envelope is made of (1) derived from (2) via (3) or (4)
1- lipoprotein
2- host membrane
3- plasma membrane
4- nuclear, ER, or other internal membranes
viral envelopes are poor in (1) but rich in (2)
1- host cell proteins
2- VAP (viral specific glycoproteins - viral attachment protein)
viral envelopes are sensitive to….
organic solvents (EtOH, chloroform, ether), detergents, drying, acid, heat
enveloped viruses are usually transmitted by…
secretions, large droplets, blood / sexual contact
enveloped viruses usually have a _____ shape
spherical or pleomorphic (ability to alter shape)
non-enveloped viruses are sensitive to…
nothing, relatively resistant to inactivation by organic solvents, detergents, drying, acid, heat
non-enveloped viruses are usually transmitted by…
fecal/oral route, fomites, small droplets
non-enveloped viruses are released by infected cell via…
cell lysis
list the viral protein types
- VAP (viral attachement proteins) / peplomers
- viral polymerase
- matrix proteins
- immediate early phase, early phase, late phase proteins
_____ are viral proteins that facilitate host cell entry
VAP (viral attachement proteins) / peplomers
list the functions of viral matrix proteins
(present between nucleocapsid/envelope)
- stabilize organization of viral glycoprotein
- directs viral genome to intracellular sites of viral assembly
- facilitate virus assembly and budding
after the initial infection of a virus into a host cell, the viral particles disappear in the (1) phase which coincides with (2) period, where (3) occurs; (1) is followed by (4) which ends in the release of viruses
1- eclpise
2- latent period
3- viral genome controls host cell protein machinery and directs it to produce viral components
4- maturation
list the stages in viral replication
1) attachment
2) penetration
3) uncoating (release of nucleic acids)
4) macromolecular synthesis
5) posttranslational modifications
6) assembly
7) release (lysis of cell or budding out)
list the steps that occur in the Macromolecular Stage of viral replication
1) EARLY mRNA and protein synthesis: proteins shut off host cells and replicate viral genome (if needed)
2) replication of genome
3) LATE mRNA and protein synthesis: structural proteins
Early proteins function to (1)
Late proteins function to (2)
1- promote viral replication
2- provide structural assistance
what are the 2 possible life cycles of bacteriophages
- Virulent / Lytic phage (kills host following infection)
- Lysogenic / Temperate phage (eventual return to Lytic phage): prophage and integration into host
describe the Lysogenic / Temperate phage
- host is not immediately killed following infection
- phage genome –> prophage / provirus –> integration in host chromosome or as independent replicating entity equal to that of host genome
define viral tropism and its factors
-limitation of virus to single organ / tissue / specialized cell type or a range of any
- VAPs in outer coat (envelope, capsid) target receptors on host cell (susceptibility)
- transcription factors allow expression of viral genes
- Permissivity: cell enzyme pathways to produce viral proteins
list the 2 methods of penetration and uncoating-enveloped viruses
1) fusion
2) Endocytosis and acidification
describe fusion as a penetration and uncoating-enveloped viruses technique
- virus glycoproteins attach to host cell receptors
- envelope-membrane fusion
- capsid enters, is uncoated, released into cytosol
describe endocytosis and acidification as a penetration and uncoating-enveloped viruses technique
- host cell membrane engulfs virus including envelope
- capsid is uncoated
- increased acidity allows viral genome to escape endosome and enter cytoplasm
list the 2 methods of penetration and uncoating non-enveloped viruses
1) direct entry across plasma membrane
2) endocytosis
describe direct entry across plasma membrane as a penetration and uncoating non-enveloped viruses technique
- virus attaches to host cell receptor
- sinks into membrane
- injects genome through pore into the cell
describe endocytosis as a penetration and uncoating non-enveloped viruses technique
- virus is engulfed
- capsule is uncoated
- viral genome leaves endosome into cytoplasm
(T/F) capsid formation always undergoes self-assembly
F- some use chaperones to fold the capsomeres
viral release occurs through a (1) or (2) mechanism
1- exocytosis: capsid uses cell membrane to form envelope laced with viral proteins (more common for enveloped viruses)
2- cell lyses (more common for non-enveloped viruses)
describe the two viral enzymes that work against the Central Dogma of Biology
- RNA dependent DNA polymerase (reverse transcriptase): RNA –> DNA
- RNA dependent RNA polymerase (RNA replicase): neg. sense RNA –> pos. sense RNA
describe the features of viral mRNA
- 5’-5’ N7-methylguanosine triphosphate cap
- poly-A tail (100-200 A residues)
when viruses replicate in the cytoplasm instead, its mRNA can makes it own 5’ cap or….
create 3D RA structure known as Internal RIbosomal Entry Site Element (IRES)
list the 4 ways to produce viral proteins via transcription
- individual mRNA for proteins (continuous genome)
- segmented genome
- one single long polyprotein –> cleaved into individual proteins
- frameshift- change reading frame to transcribe individual mRNA/protein
in viruses that make long polyproteins, they are cleaved via (1) to make individual proteins, which is a key target for (2)
1- proteases
2- viral therapy (protease inhibitors)
(1), aka (2) viruses cannot replicate without a helper virus; (3) is a great example
1- defective
2- satellite
3- Hep D / HDV
describe components of HDV
- ssRNA
- only infects cells infected by HBV (helper virus)
- utilizes HBV surface antigen (HBsAg) for entry into host cell
10-15% of Prion diseases, aka (1), are developed via (2) mutation on chromosome (3), but most are developed via (4)
1- transmissible spongiform encephalopathy
2- Autosomal Dominant
3- chr. 20
4- spontaneous (PrP-c –> PrP-Sc)
____virus requires cells undergoing DNA synthesis to replicate
parvovirus
____virus stimulates cell growth and DNA synthesis
papovavirus
____virus stimulates cell growth, cell makes RNA intermediate, encodes RNA transcriptase
adenovirus
____virus stimulates cell growth, encodes its own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis, establishes latent infection
herpesvirus
____virus encodes its own polymerases and enzymes to provide deoxyribonucleotides for DNA synthesis, replication machinery, and transcription machinery in cytoplasm
poxvirus
this group of viruses has (+) RNA genome reseembling mRNA and is transcribed into polyprotein; (-) RNA template is used for replication
picornaviruses, togaviruses, flaviviruses, caliciviruses, coronaviruses
this group of viruses has (-) RNA genome as template for individual mRNAs and full-length (+) RNA template is required for replication
orthomyoxoviruses, paramyoxviruses, rhabdoviruses, filoviruses, bunyaviruses
____viruses have (+/-) segmented RNA genome as mRNA template; (+) RNA can be encapsulated to generate (+/-) RNA –> more mRNA
reoviruses
____viruses have (+) RNA that is converted into DNA and is integrates into host chromatin and transcribed as cellular genes
retroviruses
briefly define the 7 viral groups via Baltimore Classification
I- dsDNA (+/-)
II- ssDNA (+ or -)
III- dsRNA (+/-)
IV- ssRNA (+)
V- ssRNA (-)
VI- ssRNA (+) Retrovirus (has reverse transcriptase)
VII- partial dsDNA (+/-) Retrovirus
reverse transcriptase is also known as…
RNA dependent DNA polymerase
Group I viruses have (+/-) (ss/ds) (DNA/RNA) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus)
1- both +/- strands 2- ds 3- DNa 4- both 5- nucleus
Immediate early proteins function to (1). Early proteins then function to (2). Finally, Late proteins function to (3).
1- take over cell command
2- target genome replication
3- structural- translocate into nucleus to form capsule
HSV is a group __ virus
Group I (+/-) dsDNA virus
Group II viruses have (+/-) (ss/ds) (DNA/RNA) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus)
1- either +/- 2- ss 3- DNA 4- non-enveloped 5- nucleus
Parvovirus is a group __ virus
Group II ssDNA virus
in Group II viruses ssDNA is converted to dsDNA by (1) and produce virons containing (+/-) sense DNA genome
1- host factors and DNA polymerase
2- either pos./neg. sense
Group III, IV, V viruses all have (DNA/RNA) genomes and utilize (2) for transcription and replication, skipping (3) intermediates
1- RNA genomes
2- RNA-dependent RNA polymerase
3- DNA intermediates
only group (III, IV, V) viruses can be translated by host machinery
Group IV (+) ssRNA viruses (although replication is still through RNA-dependent RNA polymerase)
Group III viruses have (+/-) (ss/ds) (DNA/RNA) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus). Their genome is also termed (6) due to its structure.
1- (+) and (-) 2- ds 3- RNA 4- non-enveloped 5- cytoplasm 6- segmented
Rotavirus is a group __ virus
Group III (+/-) dsRNA virus
Group IV viruses have (+/-) (ss/ds) (DNA/RNA) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus)
1- (+) 2- ss 3- RNA 4- either 5- cytoplasm
Poliovirus is a group __ virus
Group IV (+) ssRNA virus
(+) ssRNA genome has a (1) instead of a cap and is translated into (2)
[Group IV]
1- IRES (Internal RIbosomal Entry Site Element)
2- one single long polypeptide (includes RNA-dep. RNA poly.)
Group V viruses have (+/-) (ss/ds) (DNA/RNA) (non-/segmented) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus)
1- (-) 2- ss 3- RNA 4- either segmented or continuous 5- non-enveloped 6- cytoplasm
Rabes virus is a group __ virus
Group V (-) ssRNA virus
Group VI viruses have (+/-) (ss/ds) (DNA/RNA) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus)
1- (+) 2- ss 3- RNA 4- enveloped 5- nucleus [RETROVIRUSES}
HIV is a group __ virus
Group VI (+) ssRNA retrovirus
what is a provirus
when viral genome is integrated into host genome (8% of human genome is from viral origin- possibly tumorigenic)
Group VII viruses have (+/-) (ss/ds) (DNA/RNA) genomes. They are (non-/enveloped) and replicate in (cytoplasm/nucleus).
1- (+/-) 2- partial ds (partial ss) 3- DNA 4- enveloped 5- nucleus
HBV is a group __ virus
Group VII partial (+/-) dsDNA retrovirus
why can HBV cause chronic hepatic infection that can lead to hepatocellular carcinoma (HCC)
HBV DNA (partial dsDNA retrovirus) integrates into hepatocyte –> which can be tumorigenic in nature
HDV is a group __ virus
Group V (-) ssRNA virus: requires HBV envelop proteins for infection
(T/F) DNA viruses are more stable than RNA viruses
T- RNA virus are more error prone and mutate at a faster rate
what is complementation of viruses
- 2 viruses infect host cell simultaneously
- both have defective functions in different gene locations
- both propagate b/c they can rescue each other’s defective function (complementation)
- combo progeny virus with no defective functions
define Antigenic Drift
usually RNA genomes, evolution due to small incremental changes/mutations to genome (slower than Antigenic Shift)
define Antigenic Shift
usually segemented viruses (notably influenza viruses) exchange RNA segments (reassortment) => highly pathogenic (reassorted) strain virus
describe the two types of phenotypic mixing of viruses
1) Phenotypic Mixing / Transcapisidation: genome of one virus randomly incorporates into capsid from a different or combination of both viruses
2) Pseudotypes: nucleocapsid of virus acquires envelope from another virus type
define viral recombination
recombination of viruses infecting the same host- exchanging segments of DNA/RNA (i.e. HSV-1/2)
