2. Microbiology Ch 18.2: Viruses 18.1: Monera

3. Virus: A non- cellular particle made up of genetic material and protein that can invade cells

4. Characteristics of Living Things To be Alive you need to: 1. Have cells (or be a cell!) 2. Ingest nutrients and energy 3. Be homeostatic 4. Respond to stimuli 5. Reproduce 6. Grow and develop 7. Have adaptations to the environment

5. Viruses – are they alive? Technically, no! They cannot reproduce on their own. Are obligate intracellular parasites Viruses rely on host cells for: transportation, cellular machinery, and reproduction.

6. Viruses Are Small!

7. Viruses can infect virtually every kind of organism, including humans, birds, insects, and plants.

8. Viral Structure 1. Nucleic Acid Core DNA or RNA, but never both Contains several 100’s of genes 2. Capsid A protein coat or shell (some viruses have a protective envelope outside the capsid)

9. Different Viruses

10. E.g. Bacteriophage T4 This virus attacks bacteria DNA inside a protein coat Head and tail regions

11. Bacteriophages – Infect Bacteria

12. To reproduce, viruses must invade, or infect a living host cell, which is often killed in the process. Viruses are specific. Particular viruses will infect particular organisms. Lytic cycle animation

13. Viruses Are “Host Specific” To infect a cell, the virus must first attach to it. This attachment is specific – the virus must find the type of cell that it can “fit” onto Flu Attack! How a Virus Invades your bodyFlu Attack! How a Virus Invades your body

14. Lytic Cycle 1. Infection 2. Growth and Replication 3. Lysis

15. 1.. Lytic Lifecycle The inserted genetic material instructs the host cell to produce and assemble viral structures The cell will do as it is told, until it literally bursts (= lysis)

16. 1. Infection Virus is activated by chance contact with a specific host cell Virus injects its DNA into the cell

18. 2. Growth Viral DNA (or RNA) take over the host cell A) viral DNA is indistinguishable by the host cell B) produce enzymes that can destroy the host cell’s DNA

19. 3. Replication and Lysis Viruses then direct the production of it’s own components (genetic material and protein coats) New viruses are produced so much that the host cell lyses, releasing hundreds of new viruses to carry on the same process

20. b. Lysogenic Cycle

21. Lysogenic Lifecycle E.g. Lysogenic bacteriophage 1. Viral DNA (or RNA) is injected into a host cell 2. Viral DNA (or RNA) is incorporated into the host DNA There are two pathways the bacteria may take:

22. Prophage Viral DNA is incorporated into the host DNA Both types of DNA are replicated for many generations Lytic Cycle Viral DNA and proteins are produced New viruses are assembled Host cell lyses

23. Lysogenic At an unknown time, stimulated by certain environmental factors, the prophage will enter the lytic cycle

25. Animal Viruses Similar to bacteriophage replication Have envelopes and spikes Spikes attach to the host cell membrane Once inside, uncoating releases the genetic material from the envelope and the capsid

26. Retroviruses Have RNA instead of DNA Carry reverse transcriptase – an enzyme that will convert single- stranded RNA back to double-stranded DNA This cDNA is integrated into the host cell DNA and instructs the cell to produce and assemble new viruses

27. Retrovirus Replication 9 STEPS: 1. Attachment 2. Penetration (and uncoating) 3. Reverse transcription 4. Replication (makes cDNA 5. Integration 6. Transcription of integrated cDNA 7. Biosynthesis 8. Maturation 9. Release (gets new envelope from host)

28. HIV is a Retrovirus that attacks T-cells

29. How do Vaccines work? Why can’t you use anitibiotics to treat viral infections? Why is the use of vaccines controversial? OkToBeSmart - Why vaccines WorkOkToBeSmart - Why vaccines Work TEDeD - How vaccines workTEDeD - How vaccines work Why is HIV particularly difficult for your immune system to conquer?

31. Prions Proteinaceous infectious particles Identified in 1982 by Stanley B. Prusiner (Nobel Laureate) (even though the diseases they cause have been studied for YEARS before)

32. Prions occur naturally in cells, but cause TSE diseases when mutated. TSE= Transmissible spongiform encephalopathies. Ex. Mad Cow, CJD (Creutzfeldt- Jacob Disease in Humans), chronic wasting in deer/elk

33. Mutated prions can infect brain nerve and cause them to burst leaving spaces (spongiform encephalopathy)_ US has strict Regulations On the butchering Practices of beef To prevent prions From leaving the Spinal cord and contaminating the meat (not fully proven that this would transmit them to humans or not)

34. Bacteria and Viruses Prions  Protein that can cause infection or disease is called a proteinaceous infectious particle, or prion.  Prions normally exist in cells.  Associated with diseases known as transmissible spongiform encephalopathies 18.2 Viruses and Prions Chapte r 18

35. Virus Quiz: (Open) Are Viruses alive? Explain. Viral structure – compare/contrast a typical animal virus with a bacteriophage Bacteriophage replication: compare/contrast the lytic cycle with the lysogenic cycle Animal virus replication: Compare Animal virus replication with the lytic cycle of the bacteriophage Why don’t antibiotics work on viruses? What IS a vaccine made of and how does it work to induce future immunity?