phages

Question 1

virus

Answer 1

genetic element containing either RNA or DNA that replicates in cells but is characterised by having extracellular state; single stranded or ds; small

Question 2

T/F - viruses contain organelles

Answer 2

false

Question 3

virus structure

Answer 3

inert; nucleic acid surrounded by protein capsid; sometimes other macromolecular components (envelope)

Question 4

naked virus vs enveloped virus

Answer 4

naked - capsid composed of capsomeres is outermost layer

enveloped - has capsid, but surrounding that is macromolecular envelope

Question 5

most prevalent classification system and how it works:

Answer 5

baltimore classification: class (I-VII), description (dsDNA or ssDNA). based on type of genome virus possesses

Question 6

importance of bacteria-phage interaction

Answer 6

potential controller of microbial pop. size
phage infection may influence phenotype of host (rather than killing it)
important for molecular bio (eg phage can carry coding vector)

Question 7

method of bacteriophage quantification & steps involved

Answer 7

plaque assay

1. small vol. of (known) host cells to micture
2. nutrient agar added for host cell to grow
3. plate on top of nutrient agar
4. incubate at best env. for host
5. bacterial lawns will form - wherever this is a virus particle, a bacteria will be infect, the bacteria will be killed, and then new viruses will be released. see lawn of bacterial cells and see plaques.

Question 8

what defines size of plaque? what is the unit of measurement for plaques?

Answer 8

size of virus

plaque-forming units (bc size of plaque isn’t indication of useful tings)

Question 9

problems with plaques and how to solve

Answer 9

some bacterial lawns are really thick and you like…can’t see any real information from it. solved by dilution

Question 10

virus replication

Answer 10

1. attachment of viral protein and SPECIFIC receptor (carb/glycoprotein/etc) on host
2. virus penetrated to host cell - usually complicated w phages and plant viruses. easier for animal viruses bc no cell wall. often fusion to animal cell membrane, like a vesicle, enters via endocytosis. viral genome is “uncoated” from capsid
3. transcription & translation, relying on host machinery

Question 11

permissive cells

Answer 11

allow virus multiplcation to occur

Question 12

burst size

Answer 12

amount of new viral particles

Question 13

methods of virus resistance

Answer 13

host cell lacks surface receptor

host restriction endonucleases destroy injected phage DNA

Question 14

why does t4 have lysozyme

Answer 14

will lyse cell wall, releasing new viral particle

Question 15

t4 time of replication

Answer 15

25 min

Question 16

is t4 lytic or lysogenic

Answer 16

lytic

Question 17

entry mechanism of bacteriophage

Answer 17

1. T4 comes down, tail fibres will interact w receptors in outer membrane (polysacc)
2. tail piece will undergo conformation change, contact w host cell surface
3. core gets pushed down through cell surface, lysozyme allows it to go through peptidoglycan layers
4. pore forms, genome enters

Question 18

temperate bacteriophages + example

Answer 18

lysogenic - phage dna is injected into host cell cytoplasm, can either go directly into lytic cycle or can undergo lysogeny
some will integrate genome into host genome, or genome will just exist separately as a plasmid in host, can be carried for many generation, most of the viral genes are not expressed
lambda phage is temperate that infects E. coli

Question 19

prophage

Answer 19

integrated/maintained phage genome

Question 20

lysogen

Answer 20

bacterial cell carrying prophage (phage genome)

Question 21

lysis

Answer 21

replication and release of mature virus

Question 22

lysogeny

Answer 22

integration of viral DNA into host genome or maintenance as plasmid

Question 23

transduction

Answer 23

transfer of host genes from one cell to another by virus

two types: generalized and specialised

Question 24

generalized transduction

Answer 24

host bacterial gene accidentally packaged into lytic phage and transferred to new cell

Question 25

specialised transduction

Answer 25

specific bacterial gene adjacent to site where lysogenic phage integrates into host genome is accidentally packaged and transferred to new host cell

Question 26

ecological importance of lysogeny

Answer 26

most bacteria isolated from nature are lysogens
integrated viral genes can confer virulence factors on disease-causing bacteria
viruses are the most abundant bio. entity in aquatic ecosystems - influence on nutrient cycling, bacterial and algal diversity, gene transfer

Question 27

lambda phage

Answer 27

infects e. coli

temperate phage