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

1. Viruses:Genes in a Box

2. Living or Non-living? Living Characteristics Highly organized Possess genes (hereditary) Non-living Characteristics Not made of cells Cannot reproduce on their own Which is it? Non-living

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

4. Bacteriophage Viruses “Bacteria eater” Bacteria cell Bacteriophages

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 Viruses Can stunt plant growth and diminish crop yields Most contain RNA rather then DNA as their genetic material Genetic engineering has been used to create plants resistant to some of the viruses Ex: Tobacco Mosaic Virus, Potato X Virus

11. Animal Viruses Lipid By-layer Common causes of disease Contained within an envelope Spikes helps the virus enter and leave the host cell Contain DNA or RNA as their genetic material Vaccines help prevent viral infections but most have no cures Ex: Influenza, measles, mumps, herpes, HIV, small pox, chicken pox, etc… DNA Flu Capsid Receptor Proteins

12. Enveloped Virus Reproduction Protein spikes attach to cell and envelope fuses with the cell’s membrane Virus uses the cell to reproduce and leaves without killing the cell Not all animal viruses reproduce in the cytoplasm, many do so in the host cell’s nucleus Mumps Virus

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

14. Experiments with Viruses Relatively easy to study Viral symptoms in organisms Reproduce very quickly Provided the first glimpses of how DNA works and the role it plays in heredity In 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 rabies Only had simple microscopes, were unable to see the viruses

15. Dmitri Iwanovski 1892, Russian Dmitri Iwanovski began research studying a disease effecting tobacco plants Crushed plants to extract juices Healthy plants were exposed to the extract and they then became infected The liquid was then filtered in order to remove the infection, but it still caused the plants to become diseased Concluded there must be something in the infected plants that would ‘poison’ healthy ones

16. MartinusBeijerinck 1898, Professor of Microbiology in the Netherlands Also experimented with Tobacco Mosaic Virus Observed: ‘Microbe’ was smaller then bacteria Could only be cultured on living plants Suggested that some ‘microbes’ are not cellular Named the pathogen virus, Latin for toxin or poison

17. Frederick Griffith 1928, British Microbiologist Studied the affects of two versions of the bacteria that causes pneumonia, one was pathogenic (smooth) and the other harmless (rough)

18. Experimental Findings The invention of the electron microscope allowed better views of tiny objects Wendell Stanley (Princeton, NJ), in 1935, isolated the nucleoprotein linked to causing the tobacco mosaic virus by crystallization Realized a specific molecule was the root of inheritance Focused attention on the chemical make-up of chromosomes Eukaryotic chromosomes are made of DNA and protein But which was responsible for heredity?

19. Inheritance: DNA or Protein?

20. Avery, MacLeod, & McCarty 1944, NYC Revisited Griffith’s experiments 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 Treated extract with protease (digests proteins), mixed with rough bacteria and injected into rats; rat died This showed that DNA, not protein, has ability to transform cells—thus identifying DNA as the “transforming” factor

21. Alfred Hershey & Martha Chase 1952, University of Southern California Experimented with E. coli to see which part of the T2 phage was transferred during infection Labeled vDNA and viral protein with radioactive isotopes vDNA—phosphorus-32 not found in proteins v-protein—sulfer-35 not found in DNA

22. Hershey & Chase Experiment