Effects of viruses on Host cells

Question 1

cytopathic effect

Answer 1

the visible or morphologic change(s) induced in a host cell by a virus that may result in host cell damage and or death

Question 2

inclusion bodies

Answer 2

a morphologic change in cells infected by some viruses

Question 3

mechanisms of cell damage include:

Answer 3

• 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

Question 4

noncytocidal viruses

Answer 4

infect cells and actively produce infectious viral particles without causing immediate host cell death

Question 5

cell transformation

Answer 5

the changing of a normal cell into a cancer cell

Question 6

proto-oncogenes

Answer 6

• are genes whose protein products function in the signal transduction pathways that control normal cell growth, division, and differentiation

Question 7

proto-oncogene products include:

Answer 7

• growth factor proteins
• growth factor receptors
• intracellular signal transducers
• activation of nuclear transcription

Question 8

cellular oncogenes

Answer 8

• are genes whose products can transform normal cells

- abnormally expressed or mutated forms of the corresponding proto-oncogenes induced by carcinogens

Question 9

tumor suppressor genes

Answer 9

encode proteins that normally act to inhibit cell proliferation by holding the cell cycle at the G1 phase

Question 10

Rb protein

Answer 10

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

Question 11

phosphorylated state

Answer 11

promotes DNA replication

Question 12

unphosphorylated state

Answer 12

inhibits DNA synthesis

Question 13

p53

Answer 13

mediates cell cycle arrest and is required for apoptosis induced by DNA damage

Question 14

permissive cell

Answer 14

• productive infection, in which the virus completes its replication cycle, resulting in cell lysis
• not likely to cause cancer

Question 15

nonpermissive cell

Answer 15

• nonproductive infection, in which the virus transforms the cell without completing replication cycle
• likely to cause cancer

Question 16

DNA oncoproteins

Answer 16

bind to Rb and p53 proteins, inactivating them and so permitting the cell to replicate its DNA and divide

Question 17

acute transforming viruses

Answer 17

they possess v- onc genes that are derived from host cell proto-oncogenes

Question 18

chronic transforming retroviruses

Answer 18

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

Question 19

some characteristics of transformed cells

Answer 19

• 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

Question 20

Mutation

Answer 20

• a heritable change in the nucleotide sequence of the genome of an organism
• most frequent cause of genetic change in viruses

Question 21

lethal

Answer 21

the mutated virus is unable to replicate

Question 22

escape mutants

Answer 22

mutations affecting antigenic determinants of viron surface proteins, affect sensitivity of progeny to neutralizing antibody

Question 23

conditional-lethal mutants

Answer 23

results from mutations that so affect a virus that it cannot undergo certain conditions( nonpermissive), but can replicate under other.

Question 24

temperature -sensitive mutants

Answer 24

grow at low temperature (permissive) but not high temperature( nonpermissive)`

Question 25

Defective interfering mutants

Answer 25

a virus that lacks one or more functional genes for viral replication to a deletion mutation

Question 26

dual infection

Answer 26

if the viruses are dissimilar, they may replicate within the same cell as efficiently as in single infections

Question 27

genetic interactions

Answer 27

these are interactions involving the genomes of the parental virions. Resulting progeny are genetically different from either parent

Question 28

genetic recombination

Answer 28

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

Question 29

genetic reasourtment

Answer 29

this is the exchange of complete RNA molecules between genetically related viruses with segmented genomes

Question 30

non genetic interactions

Answer 30

the products of the genes that interact rather than the genome. Progeny produced are similar to the parents

Question 31

phenotypic mixing or masking

Answer 31

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

Question 32

phenotypic mixing

Answer 32

capsids composed of proteins encoded by both genomes

Question 33

phenotypic masking or transcapsidation

Answer 33

capsids specified entirely by the other genome

Question 34

viral interference

Answer 34

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