# 1 Microbiology Unit 3 -Bacterial Genetics and VirusesPart 3: Viruses•Viruses -non-living infectious agents that may infect all living things.•Commonly named according to which host is infected.•Terms–Virion: virus particle consisting of protein coat/nucleicacid.–Capsid: term for viral protein coat–Capsomere: identical protein subunits of the capsid–Nucleocapsid: Viral capsid along with tightly packednucleic acid.–Envelope: Double layer of lipid surrounding the capsid.Microbiology Unit 3 -Bacterial Genetics and Viruses# 1Part 3: VirusesMicrobiology Unit 3 -Bacterial Genetics and Viruses# 1Part 3: VirusesMicrobiology Unit 3 -Bacterial Genetics and VirusesPart 3: VirusesShape and Classification of RNA Viruses# 2 Shape and Classification of RNA Viruses# 2Shape and Classification of DNA Viruses # 2Relative Size of Viruses •Viruses 100-1000X smallerthan hosts: 10-500 nm.•Attachment via–Spikes (attachment proteinsproject from tailless capsid)–Tails (tail fibers used )–Not needed for plant viruses•Viral genome may be–Single or double stranded,DNA or RNA–DNA may be circular or linear–Very small genome.# 3/4/5Requirement for Viruses To Grow Inside Living Cells •Must have actively multiplying host cell for viral replication.•Viruses lack enzymes to make either enzymes or proteins.•Necessary to use host enzymes and cell structures for viral reproduction.•Two phases of viruses –Outside living cells: viruses are inert macromolecules –Inside living cells: viruses redirect host metabolism for viral reproduction.•Necessary Genetic Information Needed by Viruses –Viral protein coat –Replication for Viral nucleic acid–Movement of virus in and out of host.# 6# 7 Outcomes of Viral Infection of Bacteria1) Virulent or lytic phage, e.g.,T4–Redirect cell to make more phage and lyse the cell.2) Non-lytic phage, e.g.,filamentous phage -M13–Partial takover of cell metabolism to make more phagethen leak out into environment without killing cell.3) Temperate phage, e.g. Lambda (λ) phage–Produce “latent “ infections as they are incorporated intobacterial genome.–Replicate along with the host–Produce “lysogenic conversion” -coding for proteinsdifferent than those native to the host, e.g., C. diphtheriae Outcomes of Phage Infection of Bacteria# 7Bacterial Infection with Virulent TLytic Phage# 84Bacterial Infection with Temperate λ Phage# 9Transduction Review# 10•Bacterial gene transfer via bacteriophage.•General vs. specialized.–General: Any gene of the donor cell is transferred–Specialized:•Only selected genes from donor cell are transferred.•Only temperate phages are involved in transduction•Phage integrates at certain sites into the bacterialchromosome.•Examples are Lambda phage in E. coli and toxinproduction in Corynebacterium diphtheriaeGene Transfer in Bacteria -Transduction# 10Specialized Transduction Via Temperate Phage# 10 Virulent Properties Conferred to Bacterial HostsVia ProphageHost Ranges of Bacteriophage# 11•Host range of phage limited to specific bacterial species and often to only a few strains.•Important limitation factors:–Phage needs specific receptor sites on host cell surface•Receptor sites may be altered via mutation or lysogenic conversion.–Restriction modification system on host cell must be overcome •Host bacteria have 2 adjacent genes–Restriction enzyme–Modification enzyme.•Because of limited host range, DNA rarely transferred between species.。
