Viruses II, III, & Four: Host Cells , Replication, and Replicative Cycle of Phages

  1. What do viruses lack?
    What does that make them?
    • a.      metabolic enzymes and equipment for making proteins, such as ribosomes
    •                                                               i.     Makes them Obligate intracellular parasites and only replicate within host
  2. a.      Each virus can only infect cells of a limited number of host species, called the __ of the virus
                                                                  i.      Specificity due to __
    1.      “__” fit between __ and __ molecules on the outside of cells
                                                                ii.      Some have __; others so __they may only infect one
    1.      Some may only affect certain __
    • host range
    • recognition systems of viruses
    • lock-and key
    • viral surface proteins
    • specific receptor
    • broad host ranges
    • narrow
    • tissues
  3. General Replication:
    Explain beginning
    •                                                               i.      Infection begins when virus binds to host cell and injects genome
    • 1.      Endocytosis, injection, viral envelope fusion with plasma membrane, etc. 
  4. General Replication:
    Once Inside
    •                                                               i.      : reprogram the cell to copy viral nucleic acid and manufacture viral proteins
    • 1.      Host provides nucleotides, enzymes, ribosomes, tRNAs, amino acids, ATP, etc. for making viral nucleic acids and protein
    • a.      DNA polymerase of host used for DNA viruses
    • b.      RNA viruses use viral RNA polymerase
  5. General Replicatoin
    After Produced
    •                                                               i.      they self-assemble into new viruses
    •                                                             ii.      End
    • 1.      Simplest: exit of many viruses from host= damages cell
    • a.      Symptoms erupt
  6. What are the two replicative cycles of Phages
    lytic and lysogenic
  7. Lytic
    • 1.      Culminates in death of the host cell
    • 2.      Lytic is the last stage when the bacterium lyses and releases all phages
    • 3.      A phage that replicates only by a lytic cycle is a virulent phage
  8.                                                               i.      Bacterial Resistance
    1.      __ favors bacterial mutants with receptors that are no longer __
    2.      When phage DNA successfully enters a bacterium, the DNA is identified as __and cut up by __ which restrict the ability of the phage to infect the bacterium
    a.      The bacterial cells own DNA is __in a way preventing attack by its own restriction enzymes
                                                                                                                                          i.      __ can bind to altered receptors or are resistant to __
    • Natural selection
    • recognized by a particular type of phage
    • foreign
    • restriction enzymes
    • methylated
    • Phage Mutants
    • restriction enzyme
  9. Lysogenic Cycle
    • 1.      Allows replication of the phage genome without destroying the host
    • Temperate phages
  10. a.      Temperate phages
                                                                                                                                          i.      Ex: phage lambda
    1.      Phage binds to __ and injects its __, which forms a __
    a.      Role depends on __
                                                                                                                                                                                                                  i.      Lytic: __                                                                                                                                                                                                            ii.      Lysogenic: __
    • cell surface
    • linear DNA genome,
    • circle
    • cycle
    • viral genes turn host into viral-producing factory
    • lambda DNA molecule is incorporated into specific site on bacterial chromosome by viral proteins that break both circular DNA molecules and join them to each other
  11.                                                                                                                                       i.      When integrated into bacterial chromosome, the viral DNA is called __
    1.      One __gene codes for a protein that prevents __
    a.      Phage genome mostly __within bacterium
                                                                                                                                                                                                                  i.      Every bacterial replication results in replication of __ along with its own
                                                                                                                                                                                                                ii.      Copies passed to daughter cells
    • prophage
    • prophage
    • transcription of most of the other prophage genes
    • silent
    • phage DNA
  12. a.      Lysogenic implies that prophases are capable of __
                                                                                                                                          i.      Some lambda genome is induced to exit bacterial chromosome and initiate lytic cycle caused by __ that causes change in cycle
    • generating active phages that lyse their host cells
    • environmental signal
  13. a.     
    Expression of prophage genes may
    also be expressed in such a way that it alters the host’s __
Card Set
Viruses II, III, & Four: Host Cells , Replication, and Replicative Cycle of Phages