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