1. THE GENETICS OF VIRUSES Chapter 19

2. CHARACTERISTICS OF VIRUSES  Small (20nm)  Composed of RNA or DNA and protein  Capsid- protein coat that encloses the viral genome  Viral envelopes – a membrane that encloses capsid on some viruses (derived from host)

3. Comparing the size of a virus, a bacterium, and a eukaryotic cell

4. Viral structures

5. Adenovirus

6.  Bacteriophage – a virus that infects bacteria  Viruses are obligate parasites – can only reproduce within a host cell  Host Range – virus can only infect a limited number of host cells –Ex. HIV only attacks T-cells  Considered nonliving  Viruses infect all life on the planet

7. Phages

8. VIRAL INFECTION  Virus injects its genome (DNA or RNA) into host cell  Two major reproduction pathways for phages: –1. Lytic –2. Lysogenic

9. A simplified viral reproductive cycle

10. The lysogenic and lytic reproductive cycles of phage, a temperate phage

11. THE LYTIC CYCLE  Ends in death of host cell  Viruses called virulent  Viral DNA inserted into host  Host’s DNA hydrolyzed  Viral DNA makes proteins and more viral DNA  New viruses released by bursting out of host cell

12. THE LYSOGENIC CYCLE  Does not kill host cell  Called temperate viruses  Viral DNA is inserted into host cell  Viral DNA is inserted into host cell’s DNA (called a prophage)  When host cell replicates it also replicates the viral DNA section  Prophage genes are mostly inactive  Some can make harmful toxins (ex. diphtheria and scarlet fever)

13. Classes of Animal Viruses, Grouped by Type of Nucleic Acid

15. Smallpox

16. Measles

17. Polio

18. Influenza epidemic (Killed 40 million people in 1918-19)

19. Herpes

20. RNA VIRUSES  Can be transcribed to make protein  Can make more RNA with special enzymes (within capsid)  Retrovirus – contain reverse transcriptase enzyme which transcribes DNA from RNA. (reverse) –Ex. HIV  Lack error checking ability during RNA replication so higher rates of mutation

21. HIV, a retrovirus

22. HIV infection

23. VACCINES  Harmless variants, dead or derivatives of viruses that allow us to build an immunity to the real thing  Antibiotics are powerless against viruses

24. EMERGING VIRUSES  Viruses have high mutation rates  Dissemination of virus from small population to larger (airplanes)  Spread of existing viruses from other animals

25. Cancer Causing Viruses  Some viruses can cause cancer –Ex. Hepatitis B – liver cancer –Ex. Papilloma – cervix cancer

26. Hepatitis

27. INFLUENZA  Three types –Type A: can cause epidemics and found in many animals including humans –Types B and C: only in humans and no epidemics  Type A contain two proteins on capsid –H = hemagglutinin (helps virus attach to host) –N = neuroaminidase (helps release new viruses from infected cell)

28. H1N1 (swine flu) and H5N1 (avian flu)  H1N1 –Caused both flu pandemic in 1918 and in 2009 –Probably mutated in pigs and moved to humans –79% people infected were under 30 in 2009  H5N1 –Expanding host range and 50% mutation rate –Greater threat –Human to human transmission rare (so far)

29. PRIONS  Prions are infectious proteins –Diseases caused by prions: Mad cow, Creutzfeldt-Jacob, Kuru and maybe Alzheimer’s –Misfolded forms of proteins –Associated with eating infected meat –Incubate very slowly –No cure and always deadly

30. A hypothesis to explain how prions propagate

31. Bacteria and Archaea CHAPTER 27

32. Bacteria on the point of a pin

33. THREE MAIN LINEAGES OF LIFE

34. Prokaryotes  Unicellular  Contain cell wall, plasma membrane, ribosomes, DNA, and cytoplasm  First organisms to inhabit earth  Some are autotrophs and others are heterotrophs

35. STRUCTURE AND FUNTION  Three most common shapes –Cocci – round –Bacilli – rods –Helices – spiral  Usually small (1-5μm)

36. Figure 27.3 The most common shap es of prokaryotes

37.  Prokaryotic cell walls –Most walls contain peptidoglycan (sugars cross-linked with polypeptides) except archaea –Gram positive – large amounts of peptidoglycan (stain violet) –Gram negative – small amounts of peptidoglycan (stain red) Often more threatening due to lipopolysaccharides on cell walls that are often toxic –Antibiotics often inhibit synthesis of cross-links of peptidoglycan

38. Figure 27.5 Gram-positive and gram-negative bacteria

39. Figure 27.5x Gram-positive and gram-negative bacteria

40.  Some have pilli (some for “sex”)  Some have flagella (not covered by membrane)  Some capable of taxis – movement away from or toward stimuli  Prokaryotic Genome –1/1000 as much DNA –One circular chromosome (may be concentrated in a nucleoid region) –Plasmids – smaller, rings of DNA; may carry resistance genes, conjugation genes

41. Figure 27.6 Pili

42. REPRODUCTION  Binary fission – cell division; requires copying the one chromosome and then cell divides (can happen in 20 minutes)  Genetic recombination – ways that bacteria can get genes from other organisms –Conjugation (bacterial sex) –Transformation (bacteria grab foreign DNA from environment) –Transduction (viruses infect bacteria with foreign DNA)

43. Figure 27.x1 Prokaryotic conjugation

45.  Mutation is the main source of variation in prokaryotes!!

46. Figure 27.11x1 Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right)

47. DOMAIN ARCHAEA  Prokaryotes –Methogens – use H 2 to reduce CO 2 to CH 4 ; poisoned by O2, live in swamps, decompose sewage, in guts of animals (cows and termites) help digest cellulose –Extreme halophiles – like salt, purple-red scum due to bacteriorhodopsin –Extreme thermophiles – in hot springs, 60° – 80° C, deep sea vents at 150° C

48. Figure 27.14 Extreme halophiles

49. Figure 27.14x1 Hot springs, home of thermophiles

50. Figure 27.14x2 Beggiatoa, sulfur-eating bacteria

51. Figure 27.1 “Heat-loving” prokaryotes