Viruses II Bacteriophage PDF

Viruses II Prokaryotic Examples  Summary From Last Time Classification – genomes – ICTV, or Baltimore Basic Components – Capsid and Genome Capsids – Capsomeres – Helical, polygonal, complex – Naked or enveloped Genomes – RNA or DNA, SS or DS  Typically, two “life cycles” All...

Viruses II Prokaryotic Examples  Summary From Last Time Classification – genomes – ICTV, or Baltimore Basic Components – Capsid and Genome Capsids – Capsomeres – Helical, polygonal, complex – Naked or enveloped Genomes – RNA or DNA, SS or DS  Typically, two “life cycles” All viruses tend to replicate in one or both of these cycles Lytic cycle – results in cell death, spread of new virions Lysogenic cycle – Host cell stays alive – Prophage becomes part of host chromosome – Can bring in new genes to host – May mutate and get stuck DOI: 10.1134/S0026893317020066 ISSN 0026-8933, Molecular Biology, 2017, Vol. 51, No. 2, pp. 205–215.  Bacteriophage examples Viruses that infect bacteria Basic knowledge of viruses learned from bacteriophage. Most infect Gram – Two Main types – Virulent – lytic life cycle – Temperate – lysogenic life cycle  Multiplication of Virulent Bacteriophages (Lytic Cycle) Attachment Phage attaches by tail fibers to host cell Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell Biosynthesis Production of phage DNA and proteins Maturation Assembly of phage particles  Bacteria Bacterial Capsi DN l cell chromoso d A wall me Capsi d Sheat h Tail fiber 1 Attachment: Tail Base Phage plate attaches to Pin host cell. Cell wall Plasma membrane 2 Penetration: Phage penetrates host cell and injects Sheath its DNA. contracted Tail core 3 Biosynthesi s of phage component s Figure 13.10.1  Tail DNA 4 Maturation: Viral components are assembled Capsi into virions. d 5 Release: Host cell lyses and new virions Tail fibers are released. Figure 13.10.2  Lytic cycle – Phage causes lysis and death of host cell Lysogenic cycle – Prophage DNA incorporated in host DNA – Prophage replicated along with host DNA, passed on to future generations – Viral repressor prevents expression  Lysogenic Phage Important in horizontal gene transfer Phage often pick up foreign genes – Important virulence factors Streptococcus pyogenes Staphylococcus aureus Corynebacterium diphteria Vibrio cholerae E. coli O157:H7 Salmonella enterica  Temperate Bacteriophage Temperate phage: have options to their life cycle, they can: – Lyse bacteria and go through lytic phase – OR – lysogenize or incorporate their DNA into the host genome in a lysogenic phase  t Penetration Biosynthesis Maturation Release  Which Pathway Genetic Switch determines which pathway to use To prevent lytic pathway late protein synthesis must be prevented – Lambda repressor protein that represses synthesis of other lambda encoded proteins Once lambda repressor is expressed genes required for integration are turned on. Nature Chemical Biology volume 7, pages 484–487 (2011) Integration  Types of Transduction General Transduction – Any host gene can be picked up – Usually by accident – Usually at the cost of viral genes Specialized Transduction – Phage usually enters specific location on host chromosome – Becomes lysogenetic – Phage may pick up adjacent genes during excision Example of Transduction 2 3 4 5 6 Figure 13.13  Induction of Lambda Induction of lambda phage by agents that damage DNA SOS response – Repair mechanism – Removes Lambda repressor from DNA – Initiates lytic pathway proteins leading to new virus production.  In groups of Four Pick a Scribe: Be prepared to explain to the class! Group one – Summarize and detail the lysogenic phase of a temperate phage Group two – Summarize and detail the lytic phase of a temperate phage  Next Time Animal Viruses Homework Watch this short video for inspiration