Published on

Honors Biology class PPt on viruses and the discovery and understanding of DNA as the medium of heredity

1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide
  • Prokaryotes 1µm; Eukaryotes 100 µm
  • Survival of the prophage, and therefore the reproduction of the virus, depends entirely on the host cell
  • 1) RNA enters the cytoplasm 2) Enzymes remove the protein coat 3) Enzyme from virus provides a template to make more RNA strands 4) Makes mRNA to make new viral proteins 5) Synthesize new viral-genome RNA 6) New protein coats surround the new viral RNA 7) Virus cloaks itself in the plasma membrane of the host cell and leaves
  • Injected S strain (pathogenic) in to living mice, they died from heart diseaseInjected R strain (non-pathogenic) in to living mice, the mouse was unaffectedHeated virulent (S strain) to kill it, injected heated strains, the mouse stayed healthyMixed dead S strain with living, non-pathogenic R strain bacteria—mice died when injected - living cells were converted to be pathogenic - all descendants of the transformed bacteria were pathogenicConcluded there was some ‘transforming factor’ to cause hereditable changes in bacteria, but it was still unknown
  • Viruses

    1. 1. Viruses:Genes in a Box<br />
    2. 2. Living or Non-living?<br />Living Characteristics<br />Highly organized<br />Possess genes (hereditary)<br />Non-living Characteristics<br />Not made of cells<br />Cannot reproduce on their own<br />Which is it?<br />Non-living<br />
    3. 3. General Characteristics<br />Consist of a bit of nucleic acid wrapped in a protein coat – called a capsid<br />Survive by infecting a cell and using the cell’s reproductive <br /> processes to make <br /> more viruses.<br />Are VERY small, <br /> approximately 50µm<br />Affect all living <br /> organisms—plants, <br /> animals, and bacteria.<br />
    4. 4. Bacteriophage Viruses<br />“Bacteria eater”<br />Bacteria cell<br />Bacteriophages<br />
    5. 5. Phage Reproduction<br />Reproduce one of two ways<br />Phage bores a hole in the cell membrane and injects its DNA<br />1. Lytic Cycle<br />Produces many little copies of the phage within the bacteria cell<br />Then the bacteria cell lyses (breaks-open) and phages are released<br />Kills bacteria cells in the process<br />2. Lysogenic Cycle<br /><ul><li>Viral DNA is inserted into the bacterial DNA; becomes known as a prophage
    6. 6. Viral DNA is replicated, transcribed, and translated with the bacterial DNA
    7. 7. Does NOT kill the bacterial cell, no phages are created
    8. 8. Will be passed on to daughter cells with host DNA – creates a large # of bacteria cells carrying the phage/viral DNA</li></ul>Environmental factors may trigger a switch from the lysogenic to the lytic cycle<br />
    9. 9. Lytic & Lysogenic Cycles<br />
    10. 10. Plant Viruses<br />Can stunt plant growth and diminish crop yields<br />Most contain RNA rather then DNA as their genetic material<br />Genetic engineering has been used to create plants resistant to some of the viruses<br />Ex: Tobacco Mosaic Virus, Potato X Virus<br />
    11. 11. Animal Viruses<br />Lipid By-layer<br />Common causes of disease<br />Contained within an envelope<br />Spikes helps the virus enter and leave the host cell<br />Contain DNA or RNA as their genetic material<br />Vaccines help prevent viral infections but most have no cures<br />Ex: Influenza, measles, mumps, herpes, HIV, small pox, chicken pox, etc…<br />DNA<br />Flu<br />Capsid<br />Receptor Proteins<br />
    12. 12. Enveloped Virus Reproduction<br />Protein spikes attach to cell and envelope fuses with the cell’s membrane<br />Virus uses the cell to reproduce and leaves without killing the cell<br />Not all animal viruses reproduce in the cytoplasm, many do so in the host cell’s nucleus<br />Mumps Virus<br />
    13. 13. HIV Reproduction<br />Virus resembles flu or mumps viruses physically, but has a special system of reproduction<br />Retrovirus, an RNA virus that reproduces with DNA<br />Contains an enzyme called reverse transcriptase, which converts RNA into DNA<br />HIV (Human Immunodeficiency Virus) causes AIDS (Acquired Immune Deficiency Syndrome)<br />
    14. 14. Experiments with Viruses<br />Relatively easy to study<br />Viral symptoms in organisms<br />Reproduce very quickly<br />Provided the first glimpses of how DNA works and the role it plays in heredity<br />In the early 1900s, the effects <br /> of viruses could be seen in the <br /> form of outbreaks of small pox <br /> or the disturbing behaviors of <br /> animals affected by rabies<br />Only had simple microscopes, <br /> were unable to see the viruses<br />
    15. 15. Dmitri Iwanovski<br />1892, Russian Dmitri Iwanovski began research studying a disease effecting tobacco plants<br />Crushed plants to extract juices<br />Healthy plants were exposed to the extract and they then became infected<br />The liquid was then filtered in order to remove the infection, but it still caused the plants to become diseased<br />Concluded there must be something in the infected plants that would ‘poison’ healthy ones<br />
    16. 16. MartinusBeijerinck<br />1898, Professor of Microbiology in the Netherlands<br />Also experimented with Tobacco Mosaic Virus<br />Observed:<br />‘Microbe’ was smaller then bacteria<br />Could only be cultured on living plants<br />Suggested that some ‘microbes’ are not cellular<br />Named the pathogen virus, Latin for toxin or poison<br />
    17. 17. Frederick Griffith<br />1928, British Microbiologist<br />Studied the affects of two versions of the bacteria that causes pneumonia, one was pathogenic (smooth) and the other harmless (rough)<br />
    18. 18. Experimental Findings<br />The invention of the electron<br /> microscope allowed better <br /> views of tiny objects<br />Wendell Stanley (Princeton, NJ),<br /> in 1935, isolated the <br /> nucleoprotein linked to causing <br /> the tobacco mosaic virus by <br /> crystallization<br />Realized a specific molecule <br /> was the root of inheritance<br />Focused attention on the chemical make-up of chromosomes<br />Eukaryotic chromosomes are made of DNA and protein<br />But which was responsible for heredity?<br />
    19. 19. Inheritance: DNA or Protein?<br />
    20. 20. Avery, MacLeod, & McCarty<br />1944, NYC<br />Revisited Griffith’s experiments<br />Took extract from heated S strain and treated it with DNAase (digests DNA), then mixed with rough bacteria and injected into rats; the rats lived <br />Treated extract with protease (digests proteins), mixed with rough bacteria and injected into rats; rat died <br />This showed that DNA, not protein, has ability to transform cells—thus identifying DNA as the “transforming” factor<br />
    21. 21. Alfred Hershey & Martha Chase<br />1952, University of Southern California<br />Experimented with E. coli to see which part of the T2 phage was transferred during infection<br />Labeled vDNA and viral protein with radioactive isotopes<br />vDNA—phosphorus-32 <br />not found in proteins<br />v-protein—sulfer-35 <br />not found in DNA<br />
    22. 22. Hershey & Chase Experiment<br />