block D - viruses Flashcards
(100 cards)
1
Q
what are the easiest microorganisms to grow?
A
bacterial cells
2
Q
how can animal viruses (and some plant viruses) be cultivated?
A
in tissue or cell cultures
3
Q
what are typically the most difficult to grow?
A
plant viruses and you typically need the whole plant
4
Q
what is a titre?
A
its the number of infectious units per volume of fluid
5
Q
what is a plaque assay?
A
analogues to the bacterial colony; one way of measuring virus infectivity
they’re clear zones that develop on lawns of host cells and the lawn can be bacterial or tissue culture
each plaque results from infection by a single virus particle
6
Q
what are capsids formed form?
A
structural subunits
7
Q
what does icosohedral symmetry mean?
A
it means the capsid has lots of different sides
8
Q
what are the different types of viral symmetry of capsids?
A
helical symmetry
icosohedral symmetry
9
Q
what are naked viruses?
A
they’re viruses that don’t have a membrane, they’re not enveloped
10
Q
what are naked viruses less resistant to?
A
the drying effects of the environment
11
Q
what does a capsid consist of?
A
its a virion that consits of nucleic acid packaged into a protein coat
12
Q
what does a nucleocapsid consist of?
A
nucleic acid and protein packaged into a virus is called a nucleocapside
13
Q
what else can be in a cell envelope?
A
spike proteins
14
Q
what does a lyosome do to help cells get their genomes into other cells?
A
they make small holes in the cell wall and lyse the bacterial cell
15
Q
why do some virions carry nucleic acid polymerases?
A
because they’ve got RNA genomes and so they have to carry their own enzymes to replicate their genomes once they get into cells
16
Q
what do neuramideases do?
A
they allow the liberation of viral cells from the cells they’ve infected and they cleave the glycosidic bonds
17
Q
what are all the different baltimore classifications of viruses?
A
I- dsDNA (e.g. most bacteriophages, herpesviruses, poxviruses)
II- ssDNA (+) sense (e.g. parvoviruses)
III- dsRNA (e.g. reoviruses)
IV- ssRNA (+) sense RNA (e.g. picornaviruses, coronaviruses).
V- ssRNA (-) sense (e.g. rhabdoviruses, influenza viruses)
VI- ssRNA (+) sense with dsDNA intermediate (e.g. retroviruses)
VII- dsDNA with RNA intermediate (e.g. hepadnaviruses)
18
Q
why is there a massive sponteneous increase during a one step growth experiment of virions?
A
because they all have the same lifecycles and grow at the same pace from early enzymes to nucleic acid synthesis to the formation of protein coats so theyre all assembled at the same time
19
Q
what is the early phase of viral replication?
A
initiation as a whole
this consists of:
1. recognition
2. attachment
3. penetration
4. uncoating
20
Q
what is the late phase of viral replication?
A
it consists of replication and release
replication has the following steps in it:
1. transcription
2. protein synthesis
3. genome replication
4. assembly
release has the following steps in it:
1. lysis and release
2. budding and release
21
Q
what could be the receptors and viral attachment proteins involved in target cell recognition and attachment?
A
receptors- proteins, carbohydrates, glycoproteins or glycolipids
viral attachment protein- capsid, protein that extends form capsid, glycoproteins or enveloped virus
22
Q
give 1 example of a specific virus, what its target cell is and what is the receptor called?
A
HIV-1
helper T cell
CD4
23
Q
how does the process of penetration and uncoating for naked viruses go?
A
- attachment
- pore-mediatied penetration
- nucleic acid ejection
- cytoplasmic viral genome injected
it works like a hypodermic needle through the cell membrane and then the genome can enter the cytoplasm of the cell
24
Q
what are the two different ways viral cells can penetrate and uncoat their genome?
A
endocytosis- for naked and enveloped cells
membrane fusion- only enveloped
25
what are more dependant on the host; small or large viruses?
small ones
the smaller virus, the more dependant they are
26
where does transcription of the viral genome occur?
in the nucleus, but not in POX viruses because they're so big
27
what is viral transcription regulated by?
its regulated by the interaction of DNA binding proteins with regions of viral genome, they're very similar to the hosts regulatory mechanism
28
what is transcribed first of viral genomes?
the mRNA for non-structural proteins is transcribed first because they make all the other parts first before making the structural elements so that once they make the structural elements, they can burst out of the host cell
29
are genome replication and translation similar?
yes
30
what must always be formed in the replication of RNA viruses?
DSRNA replicative intermediate must ALWAYS be formed
31
what does translation of viral mRNA depend on?
it depends on host cell functions
32
what can eukaryotic ribosomes not translate?
polycistronic mRNA
33
what do viruses promote?
they promote preferential translation of their mRNA
34
is virus assembly different depending on the structure?
yes, helical and icosahedral viruses are made up differently
35
what are the different ways of release of viral cells from their host cells?
1. cell lysis
2. exocytosis
3. budding of enveloped viruses
36
what is a virus?
its a genetic element that cannot replicate independently of a living (host) cell
37
what is virology?
its the study of viruses
38
what is a virion?
its a virus particle and is the extracellular form of a virus
it exists outside of the hosyt and facilitates transmission from one host to another
it contains nucleic acid genome which is surrounded by a protein coat and in some cases, other layers of material
39
what are the phases of a virus life cycle to a susceptible host cell?
- entry (penetration)of the virion or its nucleic acid
- synthesis of virus nucleic acid and protein by cell metabolism as redirceted by virus
- assembly of capsids and packaging of viral genomes into new virirons (maturation)
- release of mature virions from host cell
40
what is the latent period of the viral life cycle made up of?
eclipse and maturation- this is when the virion stalls the growth of the bacteria when it infects the host cell and it starts to replictae its genome
41
what is the 'burst size'?
its the number of virions released after a small amount of virus has been added to a culture
42
how do you quantify bacterial viruses?
by plaque assay
43
what are plaques?
theyre areas of bacteria that have gone through their life cycle then lysed out of the cells and caused a lawn around them that cells can no longer grow
44
what are the best studied bacteriophages?
theyre the ones that infect enteric bacteria like E. coli and salmonella enterica
45
what are collars, the parts between the tail and the head of the bacteriophage, important for?
packaging DNA
46
are there any pathogenic archea known?
none know yet but its a very understudied area
47
what do viruses that infect archaea resemble?
they resemble viruses that can infect enteric bacteria
48
how many bacteriophages are present on the planet at one time and how many infcetions do they initiate per sec?
10¹⁰ bacteriophages on the planet at one time and gthey cause 10²⁵ infections per second
49
what is the oldest preditor-prey interaction?
bacteriophages and viruses
50
what does the attachment and entry of a virion into a host cell require?
complimentary receptors on the surface of a susceptible host and its infecting virus - they facilitate interactions with viruses
51
what do the host cells receptors usually carry out for the host?
normal functions like uptake of proteins or cell-to-cell interactions
52
what are some general examples of receptors on host cell membranes?
prpoteins
carbohydrates
glycoproteins
lipids
lipoproteins
complexes
53
the attachment of virion to host cell is very.......? complete the sentence
specific
54
what is a permissive cell?
its a host cell that facilitates the complete replication cycle of a virus to occur
55
what is bacteriophage T4?
its infects a virus of E. coli; one of the most complex penetration mechanisms
virions attach to cells via tail fibres that interact with polysaccharides on E. coli cell envelope
the tail fibres retract and the tail core makes contact with E. coli cell wall. the liosome-like enzyme fors a small pore in the peptodoglycan wall and the tail sheath contracts, then viral DNA is able to pass into the host cell cytoplasm
56
what are some characteristics about the T4 genome?
they're circularly permuted and terminally redundant
basically meaning that it replicates it genome in a circle, and it doesn't stop, it just keeps on going
both these factors affect genome packing
57
what are some mechanisms eukaryotes have to diminish viral infections?
immune defence mechanisms
RNA interference
58
what are soem mechanisms that prokaryotes possess to diminish viral infections?
CRISPR- this is similar to RNA interference
restriction modification system- DNA destruction system; effective only against double-stranded DNA viruses
restriction enzymes- these DNA at specific sequences to modify the hosts own DNA at restriction enzyme recognition sites to prevent cleavage of their own DNA
59
what are the T4's viral mechanisms for evading bacterial restriction systems?
- chemical modification of viral DNA (glycosylation or methylation)
- production of proteins that inhibit host cell restriction system
T4 DNA contains the modified base 5-hydroxymethylcytosien - its DNA is resistant to virtually all known restriction enzymes
60
what are the three parts of T4 genome replication and how do they work?
early, middle and late
early and middle- enzymes are needed for DNA replication and transcription
late - the head and tail proteins and enzymes are needed to liberate the matie phage particles from the cell
61
what are the early proteins produced for the replication of bacteriophage T4?
- enzymes for the synthesis and glucosylation of the T4 base hydroxymethylcytosine
- enzymes that funtion in T4 replisome
- proteins that modify host RNA polymerase
62
what are the middle proteins produced for T4 replication?
- additional proteins that modify host RNA polymerase
- production of viral proteins
63
what are the late proteins produced for T4 replication?
- theyre synthesised later
- include proteins for the virus coar
- typically structural components
- theyre synthesised in larger amounts
64
what are the steps for packaging the T4 genome?
- the precursor of the bacteriophage head is assembled
packaging motor is assembled
- double-starnded DNA is pumped into head under pressure using ATP
- after the head is filled with DNA, the tail fibres and other components are added
65
what is the virulent mode of a viral life cycle?
its when viruses lyse host cells after infection
66
what is the temperate mode of a viral life cycle?
its when viruses replicate their genomes in tandem with host genome and without killing the host
they can undergo a stable genetic relationship within the host but they can also kill cells through the lytic life cycle
67
what is lysogeny?
is a state where most virus genes arent expressend and the virus genome (prophage) is replicated in synchtony with the host chromosome
68
what is a lysogen? and what can happen to these under certain conditions?
its a bacterium containing a prophage
under certian condtions they can start to revert to the lytic pathway and begin ro produce virirons
69
what is bacteriophage lambda?
its a bacteriophage with a linear double stranded DNA genome
- it has complimentary, single stranded regions 12 nucleotides long at the 5' terminus of each strand
- upon penetration, DNA ends base-pair to form the cos site and the DNA ligates and forms double-stranded circles
- when lambda is lysogenic, its DNA integrates into E. coli chromosome at the lambda attachment sote
70
What happens when bacteriophage lambda enters the lytic pathway?
when it enters the lytic pathway, lambda synthesises long, linear concatemers of DNA by rolling circle replication
this allows conserved replication and packaging of the genome
71
what is the regulation of lytic Vs lysogenic events in lambda controlled by?
its controlled by a complex genetic switch
72
what are the two key elements in the regulation of lytic Vs lysogenic events in lambda?
cl protein (the lambda precursor)- this causes repression of lambda lytic events (this activates lysogeny)
Cro repressor- this controls activation of lytic events (represses lysogenic genes)
the physiology of the host cell is kwy to the balance of these two proteins
73
what drives bacterial evolution?
the transfer of DNA from one cell to another by a bacteriophage due to mispackaging of the bacteriophage genome
74
what are the two modes of transduction?
- Generalized transduction: DNA from any portion of the host genome is packaged inside the virion
- Specialized transduction: DNA from a specific region of the host chromosome is integrated directly into the virus genome
75
what are some examples of viceral paracitic infections?
amoebae and ciliates - spcific examples of these groups are entameoba and balantidium
flagellates and apicomplexa - some specific examples are trichomonas, cryptosporidium and toxoplasma
76
how is entamoena histolytica transmitted?
its transmitted to humans primarily through contaminated food and water
77
what is the disease amoebiasis transmitted by?
entamoeba histolytica
78
what does amoebiasis cause?
its anerobic and produces cysts (infective form which are resistant to gastic acids in the stomach). excytation of these leads to 8 trophosoites in the small intestien
the infcetion can be asymptomatic or lead to diarrhea and/or dystentry (inflammatory diarrhea)
79
what can happen if amoebiasis is left untreated?
it can invade the liver and occasionally the lungs and brain (about 10% of cases)
80
how is amoebiasis treated?
its treated with azoles, metronidazole in particular
81
how is ameobisis diagnosed?
by cysts in the stool
82
what is balantidium coli?
its a cilliated, intestinal human and swine parasite
83
whart are balatindium coli infections caused by?
cysts
84
how are Balantidium coli infections transmitted?
they're transmitted to humans by faecally contaminated water
85
how is balantidium coli diagnosed?
by stool and colon tissue analysis
86
what is the treatment for balantidium coli?
its treated with tetracycline, metronidazole`
and iodoquinol
87
what is giardia intestinalis?
its a flagellated anaerobic parasite and has mitosomes
88
what are mitosomes?
they're mitochondrial remnant organelles
89
what does giardia intestinalis produce?
highly resistant cysts and giardiasis, this is a common waterborne disease which causes diarrhea, intestinal cramps, nausea, weight loss and malaise, many people dont have symptoms and act as carriers
90
what is the diagnosis and treatment of giardia intestinalis?
diagnosis- cysts and trophozoites in faeces
treatment- metronidazole and tinidazole
91
what is trichomonas vaginalis and how is it transmitted?
its a flagellated anerobic parasite and is transmitted person to person by sex, it can also be transmitted by toilet seats, sauna benches and towels
92
what are the symptoms of trichomonas vaginalis and what is the treatment? and how is it diagnosed?
in males its mostly asymptomatic but in females it causes vaginal purulent discharge, itching and burning
its diagnosed by microscopy and cell culture from the patient secretions
efficient treatment with metroindiazole
93
what is cyrptosporidium parvum?
its a prosist that lives as a parasite in warm-blooded animals and causes diarrhea
94
how is cryptosporidium parvum spread?
it produces thick walled cells called oocysts and these are shed in the feases of infected animals, theyre then transmitted faecally through contaminated water
95
what are oocysts highly resistant to? and how do you get rid of them?
chlorine and UV radiation
you get rid of them through sedimentation and filtration methods
96
what are some uniuqe features of cryptosporidium parvum?
- the parasite develops just under the host epithelial cell membrane in an intracellular but extracytoplasmic position
- the oocyst stages are fully formed when they're expelled from the host
- there's no need for sporulation and therefore oocysts are immediately infective
- they're diagnosed in stool sample with direct florescence antibody assay
- they're treated by nitazoxanide because it interferes with anaerobic energy metabolism, the infection os also self-limited
97
what is toxoplasma gondii?
its an apicomplexan protist that lives as a parasite in warm blooded animals
98
what microorganism is the life cycle of toxoplasma gondii similar to?
cytospridium parvum and has the same immediate life stages
99
how is toxoplasma gondii transmitted?
it produces oocysts which are shed in the faeces of infected animals then theyre transmited by cats and undercooked meat
100
what are the effects of being infected by toxoplasma gondii and what are the treatments?
its mainly asymptomatic but can damage eyes, brrain and other organs in immune-compromised individuals
it can also cause birth defects
treatment- sulphadiazine and pyrimethamine; spiromycin
