viruses and bacteriophages

Question 1

method of classification of viruses

Answer 1

Baltimore method

Question 2

what is the Baltimore method

Answer 2

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

Question 3

example of why the baltimore system works

Answer 3

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

Question 4

type 1 of the baltimore system

Answer 4

from dsDNA to mRNA

Question 5

type 2 of the baltimore system

Answer 5

from ssDNA to dsDNA to mRNA

Question 6

type 3 of the baltimore system

Answer 6

dsRNA–> mRNA

Question 7

type 5 of the baltimore system

Answer 7

ssRNA-RT–> DNA/RNA–> dsDNA –> mRNA

Question 8

international committee on taxonomy of viruses ICTV

Answer 8

order- virales
family- viridae
subfamily- virinae
genus- virus
species-

Question 9

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

–> CLASS 3

Answer 9

transcription of minus strand

Question 10

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

–>CLASS 5

Answer 10

Used directly as mRNA

Question 11

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

Answer 11

transcription of minus strand

Question 12

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

Answer 12

reverse transcription – ds intermediate–> transcription of minus strand

Question 13

viruses are not

Answer 13

alive

Question 14

why are viruses’ not found on the tree of life

Answer 14

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

Question 15

virions

Answer 15

extracellular existence

Question 16

genome size of virus

Answer 16

5Kb to 1.2 MBp

Question 17

viruses can be

Answer 17

naked or eveloped

Question 18

naked virus

Answer 18

encased in capsid

Question 19

enveloped virus

Answer 19

encased first in capsid then an envelope

Question 20

nucelocapsid

Answer 20

nucleic acid and capsid

Question 21

virus recently identified that infect the mimivirus

Answer 21

virophage

Question 22

most virus’ have a ….. stranded genome

Answer 22

double stranded

Question 23

dimensions of T4 virus

Answer 23

200nm long and 80-100nm

Question 24

two lifestyles of bacteriophages

Answer 24

virulent or temperate

Question 25

basic lifestyle of a virus

Answer 25

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

Question 26

counting virus' in a lab process

Answer 26

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

Question 27

which bacteriophage lives a temperate lifestyle

Answer 27

lambda

Question 28

two pathways of temperate virus

Answer 28

lytic or lysogenic

Question 29

if a bacteriophage takes the lytic pathway

Answer 29

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

Question 30

if a bacteriophages takes a lysogenic pathway

Answer 30

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

Question 31

after induction during the lysogenic pathway

Answer 31

cell lysis can occur

Question 32

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

Answer 32

which genes dominated

Question 33

if 'cl' a lambda repressor dominates

Answer 33

lysogenic pathways

Question 34

if 'cro' dominates

Answer 34

lytic pathway

Question 35

the gene 'cl' is known as

Answer 35

the lamb repressor gene

Question 36

early events in lambda bacteriophage infection

Answer 36

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

Question 37

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

Answer 37

in the circular lambda DNA

Question 38

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

Answer 38

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

Question 39

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

Answer 39

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

Question 40

which proteins re anti terminators

Answer 40

N proteins and Q proteins

Question 41

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

Answer 41

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

Question 42

N and Q proteins

Answer 42

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

Question 43

summary of lytic cycle

Answer 43

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

Question 44

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

Answer 44

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

Question 45

lysogeny begins when

Answer 45

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

Question 46

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

Answer 46

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

Question 47

Or has three dining sites which

Answer 47

cl binds in order, from 1-3

Question 48

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

Answer 48

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

Question 49

what is required to maintain lysogeny

Answer 49

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

Question 50

although cr is produced before cl

Answer 50

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