taxonomy - viruses Flashcards
viruses are group into families that end in —-
viridea
viruses are given a genus name that end in —
virus
viruses are given a species name usually in —
English
classification is based on: 1) 2) 3) 4) 5)
1) nature of the host –> animal, plant, etc
2) type of disease caused –> e.g. centric, leukaemia, pneumonia
3) life cycle
4) naked or enveloped
5) type of nucleic acids and strandedness
life cycle depends on the —-
genome
the Baltimore classification scheme is based on:
why is it useful?
the type of genome
it is useful because the type of genome will dictate the replication mechanism
name the 2 configurations of the RNA genome
plus configuration and minus configuration
adsorption
attachment of the virus to specific receptors on the surface of the cell
plant viruses are usually introduced onto the host by ——-, or following ——
insect vectors, mechanical damage
penetration
virus genome enter the cell
—- and —– viruses , the complete vision may enter the cell
enveloped , naked
in —- viruses, the envelope may be left outside the cell such that only the —- may enter
enveloped, nucleocapsid
in naked viruses the —- may be left outside
capside
uncoating
removal of the envelope and pr the capsid by host enzymes, sometimes within lysosomes (in eukaryotes)
explain the mechanisms in which penetration may happen
1) naked viruses that have no envelope bind then inject their DNA inside the cell e..g bacteriophage
2) enveloped viruses bind then the 2 envelopes fuse together and that will be destroyed inside the host cell - frees the genome * viral glycoproteins remain in the cytoplasmic membrane
3) animal cells use endocytosis - the enveloped virus bind to the membrane and that will trigger endocytosis: the cell picks up the new thing in a new envelope so now the virus is in 2 membranes. they then get sent to the lysosome which degrade the capsid and the genome is released in the cytoplasm
latent period
eclipse + maturation
eclipse
time necessary for the host cells to replicate the viral genome and to synthesize the viral components
maturation
time needed for the different components to be assembled
release (rise period)
+mechanisms by which it can happen
- visions are detected outside the cell
- lysis: virus encoded proteins damage the cytoplasmic membrane. in bacteria, a virus encoded protein destroys the peptidoglycan layer
- budding: *enveloped viruses
burst size
number of virions released
how does release by budding occur
accumulation of the viral protein in the cytoplasm of the host cell –> the proteins result in a cluster of proteins in the membrane –> the viral capsid will bind there (underneath) and pushed through the membrane –> they fuse –> the virus is eventually released
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most bacteriophages are —, and — ; some may possess envelopes
dsDNA, naked
name the 2 types of bacteriophages
1) virulent phage: infection of host cells always leads to replication resulting in host cell lysis –> lytic pathway e.g. T4
2) temperate phage: have 2 options 1) lytic pathway 2) lysogenic pathway: becomes a prophage –> the genome of the virus will integrate the chromosome of the bacteria –> cell diviosn –> when nutrients are low (stationary phase) –> the virus gets out of the chromosome –> enters the lytic pathway e.g. lambda
T4 adsorption
attaches to the core region of LPS by the tail fibres
what happens after T4 adsorption
the tail sheet contracts, forcing the central core through the outer membrane. then tail lysozyme digest the peptidoglycan layer, forming a small pore. the phage DNA is the injected in to the cytoplasm of the host cell
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infection by temperate phage results in a:
prolonged latent state of infection (lysogeny)
prophage
phage genome within the host cell chromosome
lysogen
bacterium that contains the prophage
explain the mechanisms in which lambda replicates
1) the phage genome is dsDNA and linear with cohesive ends
2) the ends cyclize together forming a circle
3) circle can be inserted into the genome at attgama - the enzyme lambda integrates catalyzes integration of the phage genome at this side
where is lambda integrase encoded
on the phage genome
classify phage MS2
ssDNA, plus strand
SSDNA replication
minus strand must be synthesized fist by RNA replicase –> RNA depended RNA pol
the genome of DNA viruses is usually replicated in the —-
nucleus
the genome of RNA viruses is replicated in the —-
cytoplasm
herpes is a —- virus
DNA
penetration of DNA genome viruses
fusion of the cell’s cytoplasmic membrane with the virus envelope. nucleocapsid is transported to the nucleus where viral DNA is uncoated
transcription/translation of DNA viruses
1) immediate early proteins: like transcription factors and in some cases virus specific RNA pol
2) delayed early proteins: viral specific DNA pol, and other viral proteins necessary for replication
3) late proteins: nucleocapsid
assembly of DNA viruses occurs in the —-, envelope is added via a —– process though the —- membrane of the nucleus. the complete visions are the secreted out of the cell by —— pathways
nucleus, budding, inner, ER Golgi
name some examples of plus strand RNA viruses
coronavirus, poliovirus, hepatitis A
in poliovirus, the plus strand RNA serves as a template for synthesis of ——. what does this do?
a large poly protein, cleaved not proteins –> each smaller subunit has a diff fxn 1) RNA replicase: relocated RNA of the virus first be making a negative strand that will be used to make more positive strand 2) structural proteins 3) proteins that help cleave the poly proteins (proteases)
example of minus strand RNA viruses
measles, rabies, infleunza
ssDNA minus strand replicaiton
the virion needs to have the RNA pol by itself so when it gets injected the minus strand becomes positive and gets replicated based on that
example of dsDNA viruses
rotavirus
what is retrovirus
RNA viruses examples include HIV
- cancer causing viruses include: rous sarcoma virus
- plus strand
- ssRNA
components of retrovirus
1) integrase
2) proteases
3) reverse transcriptase –> RNA dependent DNA pol that RNA –> DNA
how does retrovirus enter the cell
ssRNA –> inserted into the cell –> virus gets inside the genome of the host like temperate bacteriophage –> in order to get instead into the genome it needs to get converted into DNA –> reverse transcription –> dsDNA genome version goes to the nucleus and gets instead –> the host can transcribe the genome into mRNA to make proteins
consequences of viral infection in unicellular organisms
release of virions
consequences of viral infection in multicellular organisms
1) cell death: following by the releases of visions via lysis
2) if release is slow –> budding of the virus through the membrane – doesn’t kill the cells –> called persistent infection: produces viruses slowly e.g. HIV
3) latent infection: the cell is infected same wth the genome but for some reason the virus is not replicated e.g. herpes (infected but not replicated) ** may lead to lysis
4) transformation into tumor cells
5) cell fusion
cell fusion results in —— that have —— —— and are usually —- lived
hybrid cells, chromosomal aberration, short
fusion often occurs in —– viruses
enveloped
cell fusion between the infected cell and another releases —-
nucleocapsids
transformation
a cell that has acquired immortality, characterized by uncontrolled replication.
T/F
both DNA and RNA viruses are known to cause tumours in animals and humans
true
name the 4 different mechanisms by which transformation happens
1) transduction
2) insertion of a strong promoter
3) inactivation of a tumor suppressor gene
4) expression of a viral protein that induces transformation (DNA virus)
- go over each in your notes
