Effects of viruses on Host cells Flashcards
cytopathic effect
the visible or morphologic change(s) induced in a host cell by a virus that may result in host cell damage and or death
inclusion bodies
a morphologic change in cells infected by some viruses
mechanisms of cell damage include:
- inhibition of host cell DNA replication
- selective inhibition of cellular mRNA production
- inhibition of cellular mRNA export
- shut down of host cell protein synthesis
- lysosomes release enzymes
- change in cell shape
- apoptosis
- lysis
noncytocidal viruses
infect cells and actively produce infectious viral particles without causing immediate host cell death
cell transformation
the changing of a normal cell into a cancer cell
proto-oncogenes
- are genes whose protein products function in the signal transduction pathways that control normal cell growth, division, and differentiation
proto-oncogene products include:
- growth factor proteins
- growth factor receptors
- intracellular signal transducers
- activation of nuclear transcription
cellular oncogenes
- are genes whose products can transform normal cells
- abnormally expressed or mutated forms of the corresponding proto-oncogenes induced by carcinogens
tumor suppressor genes
encode proteins that normally act to inhibit cell proliferation by holding the cell cycle at the G1 phase
Rb protein
inhibits the entry of cells into S phase by binding strongly to certain gene regulatory proteins, preventing them from acting in the nucleus to promote DNA replication
phosphorylated state
promotes DNA replication
unphosphorylated state
inhibits DNA synthesis
p53
mediates cell cycle arrest and is required for apoptosis induced by DNA damage
permissive cell
- productive infection, in which the virus completes its replication cycle, resulting in cell lysis
- not likely to cause cancer
nonpermissive cell
- nonproductive infection, in which the virus transforms the cell without completing replication cycle
- likely to cause cancer
DNA oncoproteins
bind to Rb and p53 proteins, inactivating them and so permitting the cell to replicate its DNA and divide
acute transforming viruses
they possess v- onc genes that are derived from host cell proto-oncogenes
chronic transforming retroviruses
cell transformation may resultt from insertion of retroviral promoter and enhancer elements at sites close to or even within proto-oncogenes, resulting in enhanced expression of the proto-oncogenes
some characteristics of transformed cells
- altered cell morphology and chromosomal abnormalities
- loss of contact inhibition
- piling up of cells to form a “focus” in monolayer cell culture
- tumor associated antigens
Mutation
- a heritable change in the nucleotide sequence of the genome of an organism
- most frequent cause of genetic change in viruses
lethal
the mutated virus is unable to replicate
escape mutants
mutations affecting antigenic determinants of viron surface proteins, affect sensitivity of progeny to neutralizing antibody
conditional-lethal mutants
results from mutations that so affect a virus that it cannot undergo certain conditions( nonpermissive), but can replicate under other.
temperature -sensitive mutants
grow at low temperature (permissive) but not high temperature( nonpermissive)`
Defective interfering mutants
a virus that lacks one or more functional genes for viral replication to a deletion mutation
dual infection
if the viruses are dissimilar, they may replicate within the same cell as efficiently as in single infections
genetic interactions
these are interactions involving the genomes of the parental virions. Resulting progeny are genetically different from either parent
genetic recombination
involves breaking of the nucleic acid strands, and parts of the genome of one parent is joined to part of the genome of the second parent
genetic reasourtment
this is the exchange of complete RNA molecules between genetically related viruses with segmented genomes
non genetic interactions
the products of the genes that interact rather than the genome. Progeny produced are similar to the parents
phenotypic mixing or masking
when two closely related viruses infect the same cell, the two types of progeny genomes may become encapsidated not only by their own capsids but also by hybrid capsids
phenotypic mixing
capsids composed of proteins encoded by both genomes
phenotypic masking or transcapsidation
capsids specified entirely by the other genome
viral interference
occurs when the multiplication of a super infecting virus in cell culture or in the host is inhibited because of the presence of an initially infecting virus
