The document discusses the nature of viruses, debating if they are living or non-living based on their characteristics, reproduction methods, and effects on various organisms. It covers the lytic and lysogenic cycles of bacteriophages, the structure and impact of plant and animal viruses, including significant historical experiments that enhanced the understanding of viral behavior and the role of DNA in heredity. Key figures like Dmitri Iwanowski, Martinus Beijerinck, and the Hershey-Chase experiment are highlighted for their contributions to virology and genetics.

1. Viruses:Genes in a Box

2. Living or Non-living?Living CharacteristicsHighly organizedPossess genes (hereditary)Non-living CharacteristicsNot made of cellsCannot reproduce on their ownWhich is it?Non-living

3. General CharacteristicsConsist of a bit of nucleic acid wrapped in a protein coat – called a capsidSurvive by infecting a cell and using the cell’s reproductive processes to make more viruses.Are VERY small, approximately 50µmAffect all living organisms—plants, animals, and bacteria.

4. Bacteriophage Viruses“Bacteria eater”Bacteria cellBacteriophages

5. Phage ReproductionReproduce one of two waysPhage bores a hole in the cell membrane and injects its DNA1. Lytic CycleProduces many little copies of the phage within the bacteria cellThen the bacteria cell lyses (breaks-open) and phages are releasedKills bacteria cells in the process2. Lysogenic CycleViral DNA is inserted into the bacterial DNA; becomes known as a prophage

6. Viral DNA is replicated, transcribed, and translated with the bacterial DNA

7. Does NOT kill the bacterial cell, no phages are created

8. Will be passed on to daughter cells with host DNA – creates a large # of bacteria cells carrying the phage/viral DNAEnvironmental factors may trigger a switch from the lysogenic to the lytic cycle

9. Lytic & Lysogenic Cycles

10. Plant VirusesCan stunt plant growth and diminish crop yieldsMost contain RNA rather then DNA as their genetic materialGenetic engineering has been used to create plants resistant to some of the virusesEx: Tobacco Mosaic Virus, Potato X Virus

11. Animal VirusesLipid By-layerCommon causes of diseaseContained within an envelopeSpikes helps the virus enter and leave the host cellContain DNA or RNA as their genetic materialVaccines help prevent viral infections but most have no curesEx: Influenza, measles, mumps, herpes, HIV, small pox, chicken pox, etc…DNAFluCapsidReceptor Proteins

12. Enveloped Virus ReproductionProtein spikes attach to cell and envelope fuses with the cell’s membraneVirus uses the cell to reproduce and leaves without killing the cellNot all animal viruses reproduce in the cytoplasm, many do so in the host cell’s nucleusMumps Virus

13. HIV ReproductionVirus resembles flu or mumps viruses physically, but has a special system of reproductionRetrovirus, an RNA virus that reproduces with DNAContains an enzyme called reverse transcriptase, which converts RNA into DNAHIV (Human Immunodeficiency Virus) causes AIDS (Acquired Immune Deficiency Syndrome)

14. Experiments with VirusesRelatively easy to studyViral symptoms in organismsReproduce very quicklyProvided the first glimpses of how DNA works and the role it plays in heredityIn the early 1900s, the effects of viruses could be seen in the form of outbreaks of small pox or the disturbing behaviors of animals affected by rabiesOnly had simple microscopes, were unable to see the viruses

15. Dmitri Iwanovski1892, Russian Dmitri Iwanovski began research studying a disease effecting tobacco plantsCrushed plants to extract juicesHealthy plants were exposed to the extract and they then became infectedThe liquid was then filtered in order to remove the infection, but it still caused the plants to become diseasedConcluded there must be something in the infected plants that would ‘poison’ healthy ones

16. MartinusBeijerinck1898, Professor of Microbiology in the NetherlandsAlso experimented with Tobacco Mosaic VirusObserved:‘Microbe’ was smaller then bacteriaCould only be cultured on living plantsSuggested that some ‘microbes’ are not cellularNamed the pathogen virus, Latin for toxin or poison

17. Frederick Griffith1928, British MicrobiologistStudied the affects of two versions of the bacteria that causes pneumonia, one was pathogenic (smooth) and the other harmless (rough)

18. Experimental FindingsThe invention of the electron microscope allowed better views of tiny objectsWendell Stanley (Princeton, NJ), in 1935, isolated the nucleoprotein linked to causing the tobacco mosaic virus by crystallizationRealized a specific molecule was the root of inheritanceFocused attention on the chemical make-up of chromosomesEukaryotic chromosomes are made of DNA and proteinBut which was responsible for heredity?

19. Inheritance: DNA or Protein?