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Viruses

Viruses. Alive?. They are reproduce Carry on the metabolism Organize the cell They contain enzymes, nucleic acids, carbohydrates, lipids Adapt to changing environments. How about virus?. They are reproduce, has macromolecules, adapt to changing environment  alive

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Viruses

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  1. Viruses

  2. Alive? • They are reproduce • Carry on the metabolism • Organize the cell • They contain enzymes, nucleic acids, carbohydrates, lipids • Adapt to changing environments

  3. How about virus? • They are reproduce, has macromolecules, adapt to changing environment  alive • They are not cells, lack any significant metabolism  not alive

  4. Host range: spectrum of organism can be attacked by virus • Animal virus, plant virus, bacterial virus (bacteriophages/phages) • Only attack single species  depend on receptor (proteins)

  5. 20 nm - 300 nm (1/3-1/10 bacteria) Size No ribosom, cytoplasm, nucleus Nucleic acid wrapped by protein coat Largest:77 genes – T4(1/50 x E.coli), Smallest: 3 genes

  6. Viral Structure

  7. Capsids • Composed of protein subunits called capsomeres. • Functions • Protective • Recognition/attachment to host cells • Introduction of nucleic acid into host cell

  8. Envelopes • Composition • Lipids from host cell membrane • Proteins • Glycoproteins • Function • Recognition/attachment to host cell

  9. Genome • RNA or DNA • Double or single-stranded • Segmented or nonsegmented ds DNA ss DNA ss RNA nonsegmented ds RNA segmented

  10. Viral Shape Helical Isometric (cubic)

  11. Complex Viral Shape

  12. Classification of Viruses • Host range • Very specific • Enveloped or nonenveloped • Type of nucleic acid • Shape

  13. Bacteriophage • Viruses that infect bacteria.

  14. Types of Bacteriophage • Virulent • Lytic multiplication cycle • Temperate • Lysogenic multiplication cycle

  15. E. coli host bacillus Bacteriophage Adsorption Lytic Cycle

  16. E. coli host bacillus Bacteriophage Bacterial DNA Viral DNA Lytic Cycle Adsorption Penetration

  17. E. coli host bacillus Bacteriophage Bacterial DNA Viral DNA Lytic Cycle Adsorption Penetration Lytic phase Duplication of phage components; replication of virus genetic material

  18. E. coli host bacillus Bacteriophage Bacterial DNA Viral DNA Lytic Cycle Adsorption Penetration Lytic phase Eclipse phase Duplication of phage components; replication of virus genetic material Assembly of new virions

  19. E. coli host bacillus Bacteriophage Bacterial DNA Viral DNA Lytic Cycle Adsorption Penetration Lytic phase Eclipse phase Duplication of phage components; replication of virus genetic material Maturation Assembly of new virions

  20. E. coli host bacillus Bacteriophage Bacterial DNA Viral DNA Lytic Cycle Release of viruses Adsorption Virion phase Lysis of weakened cell Penetration Lytic phase Eclipse phase Duplication of phage components; replication of virus genetic material Maturation Assembly of new virions

  21. Lysis Burst size http://www.oranim.ac.il/courses/microbiology/phagelab.htm

  22. Lysogenic Cycle lysogen

  23. Lysogenic State Prophage

  24. Phage Life Cycle Choices

  25. Lysogenic Conversion

  26. Propagation of Bacteriophage Mix with molten soft agar Infect bacteria Plate plaque

  27. Determining  Titer http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap9.html

  28. Seven steps in Generalised Transduction 1. A lytic bacteriophage adsorbs to a susceptible bacterium. 2. The bacteriophage genome enters the bacterium. The genome directs the bacterium's metabolic machinery to manufacture bacteriophage components and enzymes 3. Occasionally, a bacteriophage head or capsid assembles around a fragment of donor bacterium's nucleoid or around a plasmid instead of a phage genome by mistake.

  29. Seven steps in Generalised Transduction (cont’d) 4. The bacteriophages are released. 5. The bacteriophage carrying the donor bacterium's DNA adsorbs to a recipient bacterium

  30. Seven steps in Generalised Transduction (contd) 6. The bacteriophage inserts the donor bacterium's DNA it is carrying into the recipient bacterium . 7. The donor bacterium's DNA is exchanged for some of the recipient's DNA. http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/transduction/transduction.html

  31. Six steps in Specialised Transduction 1. A temperate bacteriophage adsorbs to a susceptible bacterium and injects its genome . 2. The bacteriophage inserts its genome into the bacterium's nucleoid to become a prophage.

  32. Six steps in Specialised Transduction (cont’d) 3. Occasionally during spontaneous induction, a small piece of the donor bacterium's DNA is picked up as part of the phage's genome in place of some of the phage DNA which remains in the bacterium's nucleoid. 4. As the bacteriophage replicates, the segment of bacterial DNA replicates as part of the phage's genome. Every phage now carries that segment of bacterial DNA.

  33. Six steps in Specialised Transduction (cont’d) 5. The bacteriophage adsorbs to a recipient bacterium and injects its genome. 6. The bacteriophage genome carrying the donor bacterial DNA inserts into the recipient bacterium's nucleoid. http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/transduction/spectran.html

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