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The World of Viruses and Bacteria: Living or Non-Living Infectious Agents

Explore the fascinating world of viruses and bacteria, from their discovery and structure to their impact on health and the environment. Learn about viral infections, bacterial classification, reproduction, and the role of bacteria in our ecosystems.

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The World of Viruses and Bacteria: Living or Non-Living Infectious Agents

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  1. Viruses and Bacteria

  2. Viruses • Living or Non-Living? • Infectious particles of nucleic acid and proteins • Cannot “live” (reproduce) outside a host

  3. History/Discovery • 1883 Adolf Mayer sought cause of Tobacco Mosaic Disease • 1935- Wendell Stanley crystallized the infectious particle—determined it was NONLIVING (can’t crystallize cells)

  4. 1st virus discovered-Tobacco Mosaic Virus (TMV)

  5. Virus Structure • Very small and simple (smaller than a ribosome ~20nm in diameter) • Made of DNA or RNA surrounded by a protein coat (capsid)

  6. Characteristics • Host specific—identify host cells by “lock and key” fit between proteins on virus and host cell receptors • *Presumed that receptors first evolved because they carried out some functions that benefited the organism

  7. Naming Viruses • International Committee on Taxonomy of Viruses names them based on three characteristics: • Type of nucleic acid (DNA or RNA) • Is the nucleic acid double or single stranded • Presence or absence of nuclear envelope

  8. Viral Infection Lytic Infection- virus enters the cell, makes copies of itself, and causes the cell to burst Lysogenic Infection- virus integrates it DNA into the DNA of the host. Viral DNA replicates with host DNA

  9. Viral Reproduction • Steps of Lytic Cycle • Attachment • Entry • Replication • Assembly • Lysis/Release (lyses the cell)

  10. Retroviruses • Contain RNA instead of DNA • Copy their RNA into DNA instead of DNA to RNA • Examples: AIDS, some cancers

  11. Bacteria • Most numerous and widespread organisms • “Discovered” with the invention of the microscope by Robert Hooke and Anton van Leeuwenhoek (1676)

  12. Classification • Two kingdoms of Prokaryotes (Prokaryotes are organisms that lack nuclei or membrane-bound organelles) • Kingdom Eubacteria: “true bacteria” , variety, 3 shapes, no phyla • Kingdom Archaebacteria: “ancient”, lives in extreme environments

  13. Archaebacteria • Methanogens–live in large intestines of animals, decompose dead organisms, produce methane gas (CH4) • Halophiles--live in salty environments • Thermoacidophiles—live in hot, acidic environments

  14. Size and Structure • 1-5 micrometers (much smaller than eukaryotic cells– 10-100 micrometers) • Unicellular (although grow in colonies) • Prokaryotic- no nucleus, no membrane-bound organelles • * CAN IDENTIFY BACTERIA BASED ON: • Shape, Cell Wall, and Movement

  15. Method of Obtaining Energy • Most are heterotrophic (mostly decomposers) • Some are autotrophic—chemotrophs and photoautotrophs • Ex: cyanobacteria

  16. Shape • Coccus (spherical)* • Bacillus (rod-shaped)* • Spirillum (spiral-shaped)* • *Arranged in chains, groups, or pairs • Pair– Diplo- • Chains– Strepto- • Groups– Staphylo— • **Example: Spherical shaped bacteria arranged in chains would be named, “Streptococcus”

  17. Cell Wall • For Eubacteria only! • Gram negative- thin cell wall consisting of a few layers of peptidoglycan • Gram positive- thick cell wall consisting of many layers of peptidoglycan

  18. Typical Bacterial Cell • Cell wall • Cell membranes • DNA (floating freely)-circular chromosome • Ribosomes • Some can move (flagella, others glide)

  19. Reproduction • Most bacteria reproduce by Binary Fission • Produces 2 identical “daughter” cells • Can grow and divide every 20 minutes • Asexual (no exchange or recombination of genetic information)

  20. Image of E. coli going through Binary fission

  21. Ways bacteria can accomplish genetic recombination (variation) • Conjugation- exchange of genes from 1 bacterial cell to another • Transformation-bacteria take up pieces offree DNA from another bacterial cell • Transduction- bacteriophage transfer portions of bacterial DNA from one cell to another.

  22. E.coli undergoing conjugation

  23. “BAD” Bacteria • Food Spoilage—smells, makes you sick • Bacterial Diseases • Only 3% of all bacteria cause human diseases • Can be treated with antibiotics and prevented through vaccination • 1st antibiotic discovered/source • Examples: pneumonia, bubonic plague, Strep. Throat, Syphilis, gonorrhea, anthrax, botulism

  24. E. coli

  25. “GOOD” Bacteria: The Importance of Bacteria • Decomposers • Help ecosystem recycle nutrients • Breakdown complex compounds into usable materials • Nitrogen fixers • Bacteria perform nitrogen fixation

  26. Importance of Bacteria (Cont.) • Human Uses • Production of food and beverages • Medicine and chemical industry • Genetic engineering • Bioremediation: Cleaning up the environment

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