Phages

Question 1

virus

Answer 1

genetic element with R/DNA which replicates in cells but has an extracellular state, metabolically inert, contain nucleic acids contained by protein capsid or other macromolecular components (envelope)

Question 2

importance of bacteria-phage interaction

Answer 2

• potential controller of microbial pop. sizes
• infection may influence phenotype of host prokaryote
• toxins made by phages can cause diseases

Question 3

Quantification of bacteriophages by plaque assay

Answer 3

1) add susceptible bacterial host cells
2) add to agar
3) pour to petri plate
4) plaques appear, holes are where the viruses are
5) use dilution factor to find original number of viruses

Question 4

General steps of virus replication

Answer 4

Phage lytic cycle:

• attachment: highly specific interaction between viral protein(s) & specific receptor on host cell surface
• penetration of host bacterium is complex; obligatory for phage replication to occur
• “permissive” cells: allow virus multiplication to occur
• -resistance to virus can arise if host cell lacks surface receptor, or if host restriction endonucleases can destroy injected phage DNA
• once viral components have been synthesized by host’s metabolic machinery, new viral particles self-assemble
• mature phage particles released when host cell lyses

eg. T4, a dsDNA infecting E.Coli

Question 5

Entry mechanism of bacteriophages

Answer 5

1) tail fiber attach to receptors
2) base of cell contacts host cell surface
3) inner core tube extends into the host cell wall
4) transfer of DNA through a pore formed in lipid bilayer

Question 6

lysogenic cycle

Answer 6

bacterial cell carrying integrated phage genome passed to future generations during cell division

Question 7

lambda phage

Answer 7

gets integrated into host DNA, can be induced to mature virus and lyse

Question 8

transduction

Answer 8

transfer of host genes from one cell to another by a virus

Question 9

generalized transduction

Answer 9

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

Question 10

specialized transduction

Answer 10

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

Question 11

Bacteriophages are important in the community

Answer 11

-most bacteria isolated from nature are lysogens