Micro Chapter 13
non-enveloped viruses are released when
when the host cell dies
plaques
zones of clearing
The relationship between viruses and their animal hosts can be divided into two major categories
1. acute infections 2. persistent infections
what are three ways that bacteria defend themselves against phages?
1. altering receptor sites 2. restriction modification systems 3. CRISPR system
what are the 5 steps in lytic phage infections?
1. attachment 2. Genome Entry 3. synthesis of phage proteins and genome 4. assembly 5. release
chronic infections
characterized by continuous production of low levels of viral particles
a generalized infection cycloe of animal viruses has 5 steps
1. attachment 2. genome entry 3. synthesis 4. assembly 5. release
two general types of persistent infections
1. chronic 2. latent
in synthesis step, production of viral particles in an infected cell requires two distinct but interrelated events
1. expression of viral genes 2. synthesis of multiple copies of the viral genome
enveloped viruses enter host cell by one of two methods
1. fusion with host membrane 2. endocytosiis
two key characteristics used to classify viruses
1. genome structure 2. hosts they infect
a virus is generally one of three shapes
1. icosahedral 2. helical 3. complex
acute infections
characterized by the sudden onset of symptoms of a relatively short duration
early proteins include 2 things
1. nuclease that degrades the host cells DNA 2. proteins that modify host cells rna polymerase so that it no longer recognizes bacterial promoters.
whats the two functions of the capsid?
1. protect the nucleic acid from enzymes and toxic chemicals of environment 2. carry enzymes required by viruses for infection of host cells
most DNA viruses multiply where
in the nucleus
t/f viruses contani only a single type of nucleic acid--either rna or dna but never both
true
which two enzymes combine and act in restriction modification systems?
1. restriction enzymes- recognize short nuleotide sequences in foregin DNA and cut the DNA molecule at sequences 2. modification enzymes- protects the host cells own DNA from the actions of the restriction enzyme
RNA viruses that have a single strand (+)
viral RNA can immediately bind to host cell ribosomes and be translated to make proteins
virus repolication often depends on _________ ____________ __________ which are potential targets of antiviral drugs
virally encoded enzymes
You have a dam mutant. You want to make a double mutant with dam topA. You decide to use phage transduction approach. Which phages you need to use: T4/P1 or λ?
Lamda phage only attatches in one specific spot, this spot may not be close to either of the sites so T4 is used because it is a generalized phage that could attatch in a few different spots
persistent infections
can continue with or without symptoms for years
protein coat aka
capsid
lytic phage infections
virulent phages exit host at the end of the infection usually by lysing the cell
antigenic shift
when a new subtype of a virus is formed by reassortment between different viruses
What would happen if bacterial viruses are mixed with growing bacterial cells?
-bacteria will be lysed and clear zones will be formed
replication strategy of viruses can be divided into three general categories
1. DNA viruses 2. RNA viruses 3. reverse transcribing viruses
How bacterial cells are hijacked by phage: 1. By making early viral proteins that often are associated with the replication of viral nucleic acid 2. By producing nucleases to destroy host DNA so that no host DNA is transcribed but only phage DNA is transcribed. 3. By using pre-existing bacterial enzymes for phage transcription and translation. 4. All 1 2 3 involved. 5. Only one of them likely because virus is too small to have many functions.
4
Phage have Only one kind of nucleic acid a protective protein coat. Only one type of enzymes. a single shape. a wide host range. a) 1, 2 b) 2 ,3 c) 3, 4 d) 4, 5 e)1, 5
A
The tail fibers on phages are associated with a. attachment. b. penetration. c. transcription of phage DNA. d. assembly of virus. e. lysis of host.
A
A Virus that multiply in a bacterial cell that contains DNA in chromosome and RNA in ribosome can carry in its genome a. Both DNA and RNA, like a bacterial cell that contains DNA in chromosome and RNA in ribosome. b. Only DNA or RNA not both. c. Only DNA and proteins. d. DNA and lipids. e. RNA and polysaccharides.
B
Temperate phages often 1. lyse their host cells. 2. change properties of their hosts. 3. integrate their DNA into the host DNA, 4. kill their host cells on contact. 5. are rare in nature. a) 1, 2 b) 2 ,3 c) 3, 4 d) 4, 5 e)1, 5
B
Viral capsids are composed of a. DNA. b. RNA. c. proteins. d. lipids. e. Polysaccharides.
C
Why viruses of bacteria and plants penetrate their genetic materials into the host whereas viruses of animals enter into the host cells?
Cell wall keeps the whole virus from being able to enter in
Which is wrong regarding prophage? A. Prophage is the phage DNA that is integrated into bacterial chromosome. B. Temperate phages usually do not lyse the cells. C. Lysogen carries prophage. D. Prophage is lysogen. E. All wrong
D
The phage that infect E. coli can not attack Pseudomonas because of 1. Phage specific host receptors 2. Phage specific restriction-modification system. 3. Lysogeny. 4. Mutation. 5. Only 1 and 2 likely.
E
Viruses are a. Obligate intracellular organisms. b. Prokaryotic or eukaryotic parasites. c. One domain of life. d. Able to replicate both inside and outside cells. e. Non-living parasites.
E
Which is wrong regarding M13? A. Its DNA is single stranded. B. It is filamentous and enters a cell via F pilus C. It uses host enzymes to replicate DNA D. It is released without cell lysis E. It also lyses cells as T4 does.
E
An antibiotic is added to a growing culture of E. coli, resulting in death of the cells. If bacteriophage are added, would the phage replicate in the cells?
No replication of phage in dying cells because viruses only replicate in living cells
RNA virus that have single strand (-)
RNA must first be copied into a (+) strand by a replicase before protein synthesis can occur
Why does ultraviolet light of lysogens lead to induction of a temperate phage and cell lysis?
SOS repair system turns on, activates protease that destroys repressor protein responsible for maintaining integration of prophage, then the prophage is excised and phage enters lytic cycle
Why do the transducing virulent T4 phage not lyse the bacterial cells they invade The T4 are temperate. The T4 are prophage. The T4 are mutated. The T4 are defective.
The T4 are defective
each plaque represents
a plaque forming unit initiated by a single phage particle infecting a cell.
most enveloped viruses are released by
budding
titer
concentration of infectious phage particles in the original phage suspension
viroids
consist solely of a small single stranded RNA molecule that forms a closed ring
synthesis of phage proteins step in lytic phage infection
consists of early proteins and late proteins
virion
consists of nucleic acid surrounded by protein coat
The induction of a temperate phage by ultraviolet light results from A. damage to the phage. B. formation of thymine dimmers. C. destruction of excision enzymes. D. destruction of a repressor. E. killing of the host cell.
d
benign
do not invade nearby tissue
All phages must have the ability to have their nucleic acid enter the host cell. kill the host cell. multiply in the absence of living bacteria. lyse the host cell. have their nucleic acid replicate in the host cell. a) 1, 2 b) 2 ,3 c) 3, 4 d) 4, 5 e)1, 5
e
Lysozyme is associated with phage a. penetration. b. release. c. lysis of host d. assembly. e. All a b c .
e
non-enveloped viruses enter the cell in only one way. why?
endocytosis, because they have no lipid envelope and cannot fuse with host membrane to enter the cell
in general, which type of viruses are more susceptible to disinfectants?
enveloped viruses because these chemicals damage the envelope making the viruses non infective
genome entry step in lytic phage infection
follwing attachment, a bacteriophage injects its genome into the cell
what's special about the HIV virus?
has symptoms of both acute and persistent infections
enveloped virsus
have a lipid bilayer outside the capsid that they obtain from the host cell
temperate phages
have the option of either directing lytic infection or lysogenic infection
malignant
have the potential to mestasize
1. altering receptor sites
if a bacterium alters a given receptor that cell becomes resistant to any phage that requires the receptor for attatchment
prion proteins acumulate where?
in neural tissue
assembly stage in lytic phage infection
maturation of the phage takes place
replication of DNA viruses
most DNA viruses replicate in the nucleus of the host cell and use the host cell machinery for DNA synthesis as well as gene expression
what is a result of the fact that a virion must bind to specific receptors?
most viruses can only infect a single species or a single type of tissues
antigenic drift
mutations accumulate in genes encoding key viral surface proteins eventually allowing the virus to not be recognized by immune systems
viruses that do not have an envelope are called
naked viruses
are plants capable of develping specific immunity to rid themselves of invading viruses?
no
nearly all phages are
non enveloped
does budding always destroy the cell?
not always because the membranes can be repaired after the viral particles exit
burst size
number of phage particles released
the entry of ______ can interfere with the cells own control mechanisms leading to tumor formation
oncogenes
prions are composed
only of protein
what's different about penetration between phages and animal viruses?
penetration of virions into animal viruses requires the entire virion being taken into the cell whereas only nucleic acid enters and capsid stays outside in bacterium
release stage in lytic phage infection
phage encoded enzyme lysozyme is produced which digests the host cell wall from within causing the cell to lyse and release the phages
Of two types of virions: Naked and Enveloped; which is wrong? Phage is usually enveloped by animal cell membrane AIDS viruses are often enveloped Phage lambda is naked Phage does not infect humans
phage is usually NOT enveloped by animal cell membrane
attachment step in lytic phage infection
phage particles collide with host by chance and protein on its tail attatches to a receptor on the host cell surface.
all known viroids infect ony
plants
lysogenic infection
when a phage incorporates its DNA into the host cell genome
apoptosis
programmed cell death
2. restriction modification systems
protect bacteria from phage infection by quickly degrading incoming foreign DNA through the combined action of two enzymes
lytic viral infections result in the formation of new viral particles and are called
prouctive infections
what is the silent viral genome called?
provirus
What kind of enzymatic activity does the bacterial modification system have?
restriction enzymes recognize viral DNA and modification enzymes protect the cells own dna from being cut
CRISPR system
segments of phage DNA--called spacer DNA--remain if a bacteria survives phage infeciton. this spacer DNA provides a historical record of past phage infections allowing the bacterial cell and its progeny to recognize and block subsequent infection by the same types of phages.
what is the characteristic appearance of prion infections
sponge like appearance of brain tissues
late proteins
structural components that make up the phage including those that make up capsid and tail are synthesized
nucleocapsid
the capsid together with the nucleic acid it encloses
what happens if the host cell does not have this receptor?
the cell is resistant to infection by that specific phage
what is an important aspect of either type of persistent infection?
the continuous production of infectious viral particles
uncoating
the nucleic acid seperates from its protein coat before the start of replication
replication of RNA viruses
the vast majority of RNA viruses are single stranded and they replicate in the cytoplasm
what happens after a virion is taken into the cell?
the viral envelope fuses with the membrane of the endosome, releaseing the nucleocapsid into the cytoplasm
what's different about when plant viruses infect a cell?
they do not attach to specific receptors instead they enter through wonud sites in the cell wall.
what are plaque asays used for?
to quantitate phage particles in a sample
