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Viruses and Bacteria

Viruses and Bacteria. Viruses. Living or Non-Living? Infectious particles of nucleic acid and proteins Cannot “live” (reproduce) outside a host. History/Discovery. 1883 Adolf Mayer sought cause of Tobacco Mosaic Disease

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Viruses and Bacteria

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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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