1. 18.1 Studying Viruses and Prokaryotes Characteristics of Living Organisms Made up of cells Reproduce on their own Have genetic information, DNA Grow and Develop Obtain and use materials and energy (metabolism) Maintain and internal balance (homeostasis) Respond to their environment Evolve, change over time

2. 18.1 Studying Viruses and Prokaryotes Viruses, bacteria, viroids, and prions can all cause infection. Any disease-causing agent is called a pathogen. viruses 50-200 nm prokaryotics cells 200-10,000 nm prion 2-10 nm viroids 5-150 nm eukaryotics cells 10,000-100,000 nm 100 nm 1 nanometer (nm) = one billionth of a meter

3. 18.1 Studying Viruses and Prokaryotes What is the difference between bacteria and viruses? A virus is made of DNA or RNA and a protein coat. –non-living pathogen –can infect many organisms Bacteria are one- celled microorganisms that can cause infection. –living pathogen

4. 18.1 Studying Viruses and Prokaryotes Viruses differ in shape and in ways of entering host cells. Viruses have a simple structure. –genetic material (DNA or RNA) –Capsid (a protein shell) –maybe a lipid envelope, a protective outer coat capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

5. 18.1 Studying Viruses and Prokaryotes Viruses enter cells in various ways. colored SEM; magnifications: large photo 25,000; inset 38,000x –bacteriophages pierce host cells

6. 18.1 Studying Viruses and Prokaryotes –viruses of eukaryotes enter by endocytosis Viruses enter cells in various ways.

7. 18.1 Studying Viruses and Prokaryotes The different viral shapes, play a role in how viruses work. It is how they identify their host cell. capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

8. 18.1 Studying Viruses and Prokaryotes Enveloped Virus Ex: influenza

9. 18.1 Studying Viruses and Prokaryotes Helical virus Example: Rabies

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11. Polyhedral Virus Example: Foot and mouth (coxsackie virus)

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13. Viruses are specific in what they infect Most viruses are species specific –Ex. Small pox-humans only, tobacco mosaic virus- plants only, bacteriophages-bacteria only can only affect a limited range of hosts –host range is determined by the specificity of attachment to the cells, which depends on properties of both the virion's coat and specific receptors on the cell surface Some can affect a number of species with in mammals ex. Rabies

14. 18.1 Studying Viruses and Prokaryotes The genetic material in viruses differ from prokaryotes and eukaryotes. They can have either DNA or RNA, but never both. capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

15. 18.1 Studying Viruses and Prokaryotes A prion is made only of proteins. –causes misfolding of other proteins –results in diseases of the brain Ex: mad cow disease

16. 18.1 Studying Viruses and Prokaryotes A viroid is made only of single-stranded RNA. –causes disease in plants –passed through seeds or pollen –Examples: Potato spindle tuber and Coconut cadang- cadang

17. 18.1 Studying Viruses and Prokaryotes Viruses can only reproduce after they have infected host cells. They are simply packaged sets of genes that move from one host cell to another. capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

18. 18.1 Studying Viruses and Prokaryotes Bacteriophages infect bacteria. capsid DNA tail sheath tail fiber

19. 18.1 Studying Viruses and Prokaryotes Lytic infection 1. Bacteriophage injects DNA into cell 2. Viral DNA forms plasmid in host 3. May enter lysogenic cycle 4. Host makes new virus Final: Host explodes (lyses), spreading virus Well known lytic viruses: –SARS –Common cold –Influenza –Rabies –AIDS mode of HIV –Tobacco mosaic virus

20. 18.1 Studying Viruses and Prokaryotes host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle. Lytic infection causes the cell to burst. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

21. 18.1 Studying Viruses and Prokaryotes Lysogenic Cycle 1. Bacteriophage injects DNA into cell 2. Viral DNA forms prophage (part of host DNA) 3. Viral DNA replicates with host 4. Cell reproduces producing many copies of virus Final: Cell has dormant virus or may enter lytic cycle Well known lysogenic viruses: –HIV –Herpes –Hepatitis B –Varicella-Zoster (chicken pox)

22. 18.1 Studying Viruses and Prokaryotes A lysogenic infection does no immediate harm. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle.

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24. –A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated back into the host's genome. -This type of transcriptase has a high rate of error causing a higher frequency of mutations. HIV- infected white blood cell Retroviruses

25. 18.1 Studying Viruses and Prokaryotes Vaccines are made from weakened pathogens. A vaccine stimulates body’s immune system to prepare for attack from microbes

26. 18.1 Studying Viruses and Prokaryotes Vaccines 2 most commonly used types of vaccines. Both build antibodies using proteins from the injected viruses.: –Live attenuated: virus is weakened to simulate actual infection (best). –Inactivated: dead viruses injected (safest).