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Microbiology > viruses and bacteriophages > Flashcards

viruses and bacteriophages Flashcards

1
Q

method of classification of viruses

A

Baltimore method

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2
Q

what is the Baltimore method

A

method of classification bacteria; based on mode of replication and genome type

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3
Q

example of why the baltimore system works

A

some genomes have double stranded DAN which is directly copied by mRNA. Other genomes can be single stranded and must become double stranded to produce mRNA. Furthermore other genomes can be just RNA

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4
Q

type 1 of the baltimore system

A

from dsDNA to mRNA

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5
Q

type 2 of the baltimore system

A

from ssDNA to dsDNA to mRNA

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6
Q

type 3 of the baltimore system

A

dsRNA–> mRNA

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7
Q

type 5 of the baltimore system

A

ssRNA-RT–> DNA/RNA–> dsDNA –> mRNA

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8
Q

international committee on taxonomy of viruses ICTV

A 
order- virales
family- viridae
subfamily- virinae
genus- virus
species-
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9
Q

how is mRNA (+) produced from dsRNA (+-)

–> CLASS 3

A

transcription of minus strand

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10
Q

How is mRNA (+) produced from ssRNA (+)

–>CLASS 5

A

Used directly as mRNA

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11
Q

how is mRNA (+) produced from ssRNA (-)

A

transcription of minus strand

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12
Q

how is mRA (+) made from ssRNA (+) IN RETROVIRUS’

A

reverse transcription – ds intermediate–> transcription of minus strand

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13
Q

viruses are not

A

alive

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14
Q

why are viruses’ not found on the tree of life

A

they are non-living and this means they infect all bacteria, archaea and eukarya

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15
Q

virions

A

extracellular existence

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16
Q

genome size of virus

A

5Kb to 1.2 MBp

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17
Q

viruses can be

A

naked or eveloped

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18
Q

naked virus

A

encased in capsid

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19
Q

enveloped virus

A

encased first in capsid then an envelope

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20
Q

nucelocapsid

A

nucleic acid and capsid

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21
Q

virus recently identified that infect the mimivirus

A

virophage

22
Q

most virus’ have a ….. stranded genome

A

double stranded

23
Q

dimensions of T4 virus

A

200nm long and 80-100nm

24
Q

two lifestyles of bacteriophages

A

virulent or temperate

25
Q

basic lifestyle of a virus

A

first the vision will inject its DNA into the cell and its protein coat will remain on outside of the cell. The DNA will cause synthesis of nucleic acid and proteins, forming new visions. Then these visions will cause cell lysis and they will be released to the surroundings and are free to penetrate other cells

26
Q

counting virus’ in a lab process

A

1) poor mice onto solidified agar plate
2) poor mixture containing melted top agar, bacterial cells and dilute phage suspension
3) sandwich of top agar and nutrient agar
4) incubate
5) count phage plaques

27
Q

which bacteriophage lives a temperate lifestyle

A

lambda

28
Q

two pathways of temperate virus

A

lytic or lysogenic

29
Q

if a bacteriophage takes the lytic pathway

A

the viral DNA replicates, the coat proteins are synthesised and the viral particles burst out f the cell during ell lysis

30
Q

if a bacteriophages takes a lysogenic pathway

A

most of the viral genes are not express and the viral genomes, called a prophage integrates into the host chromosome.. As a prophage, the viral DNA is relocated with the host DNA during division

31
Q

after induction during the lysogenic pathway

A

cell lysis can occur

32
Q

whether the phage takes the lytic or lysogenic pathway is determined by

A

which genes dominated

33
Q

if ‘cl’ a lambda repressor dominates

A

lysogenic pathways

34
Q

if ‘cro’ dominates

A

lytic pathway

35
Q

the gene ‘cl’ is known as

A

the lamb repressor gene

36
Q

early events in lambda bacteriophage infection

A

infection by lambda phage begins when the virus attaches to a receptor on the bacterial cell walls and injects its DNA into the cell. The protein coat remains outside the cell while the phage DNA inside quickly forms into a circle

37
Q

where are the genes which determine whether the lytic or lysogenic pathway will take place found

A

in the circular lambda DNA

38
Q

lytic pathway part 1: transcription and translation of N and cro

A

Lambda DNa is first transcribed by E.coli RNA polymerase, beginning at the two key promotor sequences called Pl (promotor left) and Pr (promotor right). Two transcription termination sequences (t) cause the polymerase to stop transcription after only a few N and cro have been coped. N and cro mRNAs are then translated by E.coli host ribosomes into N and cro proteins

39
Q

lytic pathway part 2: longer transcripts are made with help of N proteins

A

N protein that has recently be translated from the N gene mRNA, now acts an an ANTITERMINATOR to block the action of the termination sequence (t). RNA pol starting at Pl and Pr transcribe through the termination sequences and create longer transcripts that include the cll and clll genes. ribosomes translate the mRNAs, producing cll and clll proteins, along with the previously produced N and cro proteins

40
Q

which proteins re anti terminators

A

N proteins and Q proteins

41
Q

Lytic pathway part 3: stimulation of phage structural gene synthesis by the Q protein

A

during the second stage of transcription, when transcripts are not truncated but eh first termination sequence, another gene called Q is transcribed and translated. this gene lies clockwise around the chromosomes a little beyond the CLL gene and is transcribed by polymerases starting at Pr. Q protein is another ANTITERMINATOR. it negates the terminating effect of a second set of termination sequences just beyond the Q gene on the DNA.allow transcription from Pr to occur continuously around the chromosomes, resulting int eh production of head, tail and finer proteins. lambda phages then assemble and burst out of the cell. this is the complete lytic cycle

42
Q

N and Q proteins

A

allow transcription from Pr to occur continuously around the chromosomes, resulting in the production of head, tail and finer proteins. lambda phages then assemble and burst out of the cell. this is the complete lytic cycle

43
Q

summary of lytic cycle

A

1) Cro and N are made after transcription from Pr and Pl
2) N binds RNA polymerase to read through termination sequences
3) allows further transcription for production of the proteins

44
Q

lysogenic pathwya, part I: lambda repressor (cl) synthesis from Pe

A

The early events of lysogenic and lytic pathways are the same up through to the production of Cll and Clll proteins. Lysogeny begins when the lambda repressor gene (cl) is transcribed and translated . Cll activates transcription at a promotor sit celled Pe

45
Q

lysogeny begins when

A

the lambda repressor gene (cl) is transcribed and translated. Cll protein activates transcription at a promotor site called Pe

46
Q

lysogenic pathway, Part 2: lambda repressor protein (cl) blocks synthesis from Pr and the lytic pathway genes

A

at this point during infection, early transcription and translation have produced the N, Cro, Cll, Clll and now the cl proteins. The c and cro proteins now ‘compete’ with each other for donation of transcription events

47
Q

Or has three dining sites which

A

cl binds in order, from 1-3

48
Q

the important point for the decision between lysis and lysogeny s that binding of cl to Or or Ol turns off

A

gene expression from Pr and Pl and therefore block the lytic pathway

49
Q

what is required to maintain lysogeny

A

Lambda repressor gene (cl). if it is is destroyed in lysogenic cell, the lytic cycle will ensue

50
Q

although cr is produced before cl

A

cl has a higher affinity for the operator sites than cro and can therefore bind to them at lower expression levels

Microbiology (25 decks)

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