part 5

Bacteriophages

  • Definition: Bacteriophages, or phages, are double-stranded DNA viruses that specifically infect bacteria.

    • They are described as having a sci-fi appearance, resembling a spider.

    • An alternative analogy: Plungers with spider legs.

  • Infection Processes:

    • Bacteriophages can undergo different cycles:

    • Lysogenic Cycle (Lysogeny):

      • In this cycle, the bacteriophage DNA gets incorporated into the bacterial chromosome.

      • This integrated DNA is referred to as a prophage and can persist within the bacterial cell without causing lysis.

    • Lytic Cycle (Lyse):

      • The virus hijacks the bacterial machinery to produce new virus components, ultimately leading to cell lysis and release of new phage particles.

      • Transitioning from the lysogenic to the lytic cycle can occur, which emphasizes the ability to reverse back to the lytic cycle.

  • Transduction:

    • Transduction occurs when a bacteriophage mistakenly incorporates bacterial DNA into its genome during the change from the lysogenic to the lytic cycle.

    • This process can inadvertently transfer bacterial DNA from one bacterium to another, serving as a means of horizontal gene transfer, also known as an accidental gift from the virus.

  • Mechanisms of DNA Integration:

    • Visual representation:

    • Picture illustrates a simplification using colored strings to represent DNA:

      • Circular strings with segments dyed to indicate areas of interest.

    • Excising DNA:

    • Requires precise cutting at designated locations to retrieve the viral DNA without disrupting the bacterial genome.

    • An analogy is made where if tasked with cutting circular strings, only a limited number can be accurately cut before mistakes arise, mirroring the challenges in DNA excision by the virus.

  • Bacterial Defense Mechanisms:

    • Bacteria employ restriction enzymes (restriction endonucleases) to combat incoming viral DNA.

    • These enzymes act by recognizing and cutting foreign DNA, helping bacteria protect themselves against viral infections.

    • Example: Research and practical applications involve electrophoresis gels where restriction enzymes are frequently utilized.

Bacterial Phage Infections

  • Phage Lifecycle Terms:

    • Prophage: Integrated form of the bacteriophage's DNA within the bacterial chromosome during lysogeny.

    • Provirus: The form that a virus takes when it integrates into the host's genetic material (similar concept in human viruses).

  • Viral Behavior:

    • Discussion of bacterial phages leads naturally into human viruses and their impacts on health.

Herpes Viruses Survey

  • General Characteristics:

    • Students must be familiar with the following concepts regarding viruses:

    • Whether it is a DNA or RNA virus.

    • If it is naked or enveloped.

    • Modes of entry into host cells:

      • Fusion or receptor-mediated endocytosis.

      • Modes of exit: budding or lysis.

  • Specific Viruses and Conditions:

    • Herpes Simplex Virus (HSV):

    • HSV-1 typically causes oral herpes.

    • HSV-2 is associated with genital herpes.

    • These infections are lifelong, with the capability of flare-ups but no cures.

  • Varicella-Zoster Virus (VZV):

    • Responsible for chickenpox (systemic disease) and shingles (reactivation of the virus).

    • Immunization: A live vaccine is administered to children to prevent infection.

    • Transmission: Primarily via respiratory droplets, not through direct contact with the chickenpox lesions.

  • Epstein-Barr Virus (EBV):

    • Infects B cells leading to Infectious Mononucleosis commonly known as mono.

    • Symptoms mimic a severe cold:

    • High fever, fatigue, prolonged illness.

    • Nicknamed the kissing disease because of its transmission patterns, especially prevalent among high school students.

    • When EBV infects B cells, they may morph into atypical lymphocytes resembling squished cells.

Conclusion

  • Review consolidation:

    • Importance of understanding viral mechanisms and their classifications.

    • Practical implications: Knowledge of viral infections aids in diagnostics and therapeutic strategies.