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Understanding T4 Bacteriophages and Their Impact on Bacterial Infections

T4 bacteriophages are viruses that specifically target and inject their DNA into Escherichia coli bacteria, effectively hijacking the bacterium's genetic machinery. As obligate intracellular parasites, they can only survive within a host cell. With diameters as small as 20nm, they are among the tiniest viruses, making them smaller than ribosomes. The lytic cycle results in the destruction of the host cell, while the lysogenic cycle allows viral DNA to integrate with the host's DNA. This document covers various viral life cycles, discusses other viruses like HIV and Ebola, and touches on prions and viroids.

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Understanding T4 Bacteriophages and Their Impact on Bacterial Infections

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  1. Lunchtime!! T4 Bacteriophages

  2. T4 Bacteriophage • Bacteriophage – virus that attacks bacteria • Attacks Escherichia Coli bacteria • Injects its DNA into the bacterium’s DNA • Virus takes over the bacterium’s genetic mechanism • Called an obligate intracellular parasite • Obligate – only exists in certain cases • Intracellular – Internal or inside cell • Parasite – lives off another organism

  3. Viral Structure • The smallest viruses are 20nm in diameter, smaller than a ribosome • What does a ribosome do? • What does that mean for its size relative to an animal cell?

  4. Who’s bigger?

  5. Let’s talk about viruses #1 • 1. HIV/AIDS • In 2007, 33.2 million with HIV/AIDS • 2.1 million fatalities from HIV • 68% of infections are in Sub-Saharan Africa • 2.5 million new infections in 2006 • Retrovirus

  6. Viral Images

  7. Let’s talk about viruses #2 • 2. Influenza • 7th leading cause of death worldwide, but not in the US • Causes widespread pandemics every decade or so • Fatality is more likely in the elderly & infants • Avian influenza in the 1990’s was the last major pandemic

  8. Let’s talk about viruses #3 • 3. Ebola Hemorrhagic Virus • “Occasionally, Internal and external hemorrhage from orifices, such as the nose and mouth may also occur, as well as from incompletely healed injuries such as needle-puncture sites.” • Mortality rates are generally high, ranging from 50% - 90% • Ebola is referred to as a “slate wiper” due to its remarkably high case fatality rate

  9. Ebola outbreak in Congo

  10. Are Viruses alive? • They have DNA (or RNA) • They are not able to reproduce on their own • They infect other cells in order to perpetuate their life cycle • Viruses can be crystallized, but no other cells can be crystallized • May contain a membranous envelope

  11. Viral Genomes • Basically – nucleic acid with a protein coat • Some will have DNA (2-strands or 1-strand) • Papillomavirus, Herpesvirus, & Smallpox • Parvovirus (1-strand) • Others have RNA (2 or 1 strand again) • HIV, Influenza & Ebola • Amount of genes also varies widely depending on the virus

  12. Capsids & Envelopes • Capsid – Protein shell enclosing the viral genome • Rod-shaped, polyhedral, or more complicated (T4) • Capsids are built from protein subunits called capsomeres • Envelope – Helps viruses infect their hosts • Derived from the membranes of the host cell • Host phospholipids & membrane proteins

  13. Viral Life Cycle Animation(s) • 19_04SimpViralReproCycle

  14. Simple Viral Reproductive Cycle

  15. 2 Types of Viral Life cycles • Lytic • Virulent cycle • Results in death of host cell • New phages are produced, host cell wall destroyed, and progeny (daughter viruses) are released to infect other cells • Lysogenic • Viral DNA is incorporated into host DNA • This viral DNA is called prophage (provirus in euks.) • Infection silently spreads to daughter cells

  16. Lytic Cycle Animation • 19_05PhageT4LyticCycle

  17. Lytic Cycle

  18. Lytic vs. Lysogenic Cycle • 19_06LysogenicLyticCycle

  19. Lytic vs. Lysogenic Cycle

  20. HIV Life Cycle • 19_08HIVReproCycle

  21. Viroids & Prions • Viroids • Just RNA • Significantly smaller than viruses • Infect plants • Prions • Proteins that are capable of infecting cells • No DNA or RNA • Causes degenerative brain diseases • CJD (Creutzfeldt-Jacobs disease V1) • Bovine Spongiform Encephalopathy (BSE)

  22. Prions & Alzheimer's • Prions form into incorrect shape in CJD, but not so in Alzheimer • Prions interact with plaques to allows the plaques to damage brain cells • Amyloid-beta is the go between • Mechanism of prion and amyloid-beta is unknown • But sci. know there is an interaction, and this interaction = Alzheimers • Possible treatment avenue

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