Block D 3 Flashcards
viruses of archaea and bacteria
virus
genetic element that cannot replicate independently of a living (host)
virology
study of viruses
virus particle (virion)
extracellular form of a virus
what does a virion contain
nucleic acid genome surrounded by a protein coat (capsid) and in some cases other layers of material
4 phases of the viral replication attachment (adsorption) of the virus to host cell
-entry (penetration) of virion or nucleic acid
-synthesis of virus nucleic acid and protein
-assembly of capsids and packing of viral genomes
-release of mature virions from host
what type of curve is virus replication typically characterised by
one step growth curve
what is the latent period of virus life cycle
eclipse and maturation
what is burst size of virus life cycle
number of virions released
how is quantification of bacterial virus carried out
plaque assay
what do the best studied bacteriophages infect
enteric bacteria
what do most phages contain
dsDNA genomes
most bacteriophages are naked but what do some possess
lipid envelopes
what do most viruses that infect archaea resemble
those that infect enteric bacteria
how many infections are initiated per second
10^25
10^14 g phages on earth is approx. the same total mass of what
homo sapiens (50kg per person)
attachment of virion to host cell is said to be what
highly specific
attachment and entry of bacteriophage T4 requires complementary receptors on what
the surface of susceptible host and its infecting virus
what do receptors on host cell carry out for cell
normal functions (eg uptake proteins, cell to cell interactions)
what do the receptors include (in attachment and entry of bacteriophage T4)
proteins
carbohydrates
glycoproteins
lipids
lipoproteins
complexes
what does the attachment of a virus to its host cell result in
changes to both virus and cell surface that facilitate penetration
what is a permissive cell
host cell that allows the complete replication cycle of a virus to occur
what is bacteriophage T4
virus of E.coli
one of the most complex penetration mechanisms
in the attachment of bacteriophage T4 virions attach to cells via what
tail fibres
what do the tail fibres that attach virions to cells interact with
polysaccharides on E.coli cell envelope
in attachment of bacteriophage T4 the tail fibres then contract, what does the tail coremake contact with
E.coli cell wall
what do the lysozyme like enzyme form in attachment and entry of bacterio. T4
small pore in peptidoglycan
once the tail sheath has contracted what happens with the viral DNA in attachment and entry of bacterio. T4
viral DNA passes into the cytoplasm
what type of genome does T4 have
dsDNA
T4 a genome that is said to be what
circularly permuted and terminally redundant
what is restriction modification system and what is it only effective against
DNA destruction system
only against double stranded DNA viruses
example of restriction enzyme
restriction endonuclease
what do restriction enzymes do
cleave DNA at specific sequences
what does modification of hosts own DNA at restriction enzyme recognition sites prevent
cleavage of own DNA
what are the 3 viral mechanisms to evade bacterial restriction systems
-chem modif. of viral DNA (glycosylation or methylation)
-production of proteins that inhibit host cell restriction system
-T4 containing a modified base
what is the name of the modified base that T4 has that helps evade bacterial restriction systems
5-hydroxymethylcytosine
its DNA is resistant to virtually all known restriction enzymes
what are the 3 parts that the T4 genome can be divided into
early
middle
late proteins
what stages are the enzymes needed for DNA rep and transcription (replication of bacteriophage T4)
early and middle proteins
what are late proteins
head and tail proteins and enzymes req to liberate mature phage particles
what stage of proteins are needed for
the synthesis and glucosylation of hydromethylcytosine
early proteins
what stage of proteins are needed for
enzymes that function of T4 replisome
early proteins
what stage of proteins are needed for
proteins that modify host RNA pol
early proteins
what stage of proteins are needed for
additional proteins that modify host RNA pol
middle proteins
what stage of proteins are needed for
production of viral proteins
middle proteins
what stage of proteins are
synthesised later
late proteins
what stage of proteins
include proteins of virus coat
late proteins
what stage of proteins are
synthesised in larger amounts
late proteins
in the packaging of the T4 genome double stranded DNA is pumped into head under pressure using what
ATP
in packaging of T4 genome after head is filled with DNA what other components are added
T4 tail
tail fibres
+ more
virulent mode
viruses lyse host cells after infection
temperate mode
viruses replicate their genomes in tandem with host genome and without killing host
temperate viruses
can undergo a stable genetic relationship within the host
(but can also kill cells through lytic cycle)
lysogeny
state where most virus genes are not expressed and virus genome (prophage) is replicated in synrony with host chr.
lysogen
a bacterium containing a prophage
what is the genome of bacteriophage lambda
linear
dsDNA
what is bacteriophage lambda
complementary
single stranded
12 nucleotides long at the 5’ terminus of each strand
what forms upon penetration of bacterio. lambda
the cos site
what occurs once cos site has been formed
DNA ligates and forms double stranded circle
when lambda is lysogenic what happens to its DNA
integrates into E.coli chr at lamba attachment site
(attλ)
what occurs when bac. λ enters lytic pathway
λ synthesises long linear concatemers of DNA by rolling circle replication
what is the regulation of lytic vs lysogenic events in λ controlled by
complex genetic switch
2 repressor proteins
what repressor proteins causes repression of λ lytic events
(activates lysogeny)
cl protein
(the λ repressor)
what repressor protein controls activation of lytic events
(represses lysogenic genes)
cro repressor
what is the key to the balance of the 2 repressor protein in the cell
the physiology of the bacterial host
what drives bacterial evolution
transfer of DNA from one cell to another by a bacteriophage due to mispacking of the bacteriophage genome
what are the names of the 2 modes of transduction
generalised transduction
specialised transduction
generalised transduction
DNA from any portion of the host genome is packaged inside the virion
