Bacteria and Viruses

1. Bacteria and Viruses

2. BACTERIA • Bacteria -small one celled organisms • Bacteria like a warm, dark, and moist environment They are found almost everywhere: • -water -air • -soil -food • -skin -inside the body • -on most objects

3. 3 Shapes of Bacteria Bacteria are classified by shape into 3 groups: Spiral: spirilla rod-shaped:bacilli, bacillus Round: cocci

4. Bacillus anthracis - rod, vegetative stage prokaryote (bacterium)Image Number: 21185A

5. Major Structures of a Bacteria Cell • Capsule • Cell wall • Ribosomes • Nucleoid • Flagella • Pilli • Cytoplasm

6. Major Structures of a Bacteria Cell Capsule • keeps the cell from drying out and helps it stick to food or other cells

7. Major Structures of a Bacteria Cell Cell wall • Thick outer covering that maintains the overall shape of the bacterial cell

8. 7 Major Structures of a Bacteria Cell Ribosomes • cell part where proteins are made • Ribosomes give the cytoplasm of bacteria a granular appearance in electron micrographs

9. 7 Major Structures of a Bacteria Cell Nucleoid • a ring made up of DNA

10. 7 Major Structures of a Bacteria Cell Flagella • a whip-like tail that some bacteria have for locomotion

11. Major Structures of a Bacteria Cell Pilli • hollow hair-like structures made of protein • allows bacteria to attach to other cells. • Pilli-singular • Pillus-plural

12. Major Structures of a Bacteria Cell Cytoplasm • clear jelly-like material that makes up most of the cell

13. Reproduction of Bacteria • Binary Fission-the process of one organism dividing into two organisms • Fission is a type of asexual reproduction • Asexual reproduction-reproduction of a living thing from only one parent How?... The one main (circular) chromosome makes a copy of itself Then it divides into two

14. Reproduction of Bacteria BINARY FISSION Completed Bacteria dividing

15. Bacterial Cell & Nucleiod DNA Ring DNA replication Cell wall synthesis Binary Fission Cell separation

16. Reproduction of Bacteria • The time of reproduction depends on how desirable the conditions are • Bacteria can rapidly reproduce themselves in warm, dark, and moist conditions • Some can reproduce every 20 minutes • (one bacteria could be an ancestor to one million bacteria in six hours)

17. Bacteria Survival • Endospore- • a thick celled structure that forms inside • the cell • they are the major cause of food poisoning • allows the bacteria to survive for many years • they can withstand boiling, freezing, and extremely dry conditions • it encloses all the nuclear materials • and some cytoplasm

18. Bacteria Survival Bacillus subtilis Endospore-the black section in the middle • highly resistant structures • can withstand radiation, UV light, and boiling at 120oC for 15 minutes.

19. Bacteria Survival – Food sources • parasites–bacteria that feed on living things • saprophytes–use dead materials for food (exclusively) • decomposers –get food from breaking down dead matter into simple chemicals • important- because they send minerals and other materials back into the soil so other organisms can use them

20. Harmful Bacteria • Communicable Disease – • Disease passed from one organism to another • This can happen in several ways: • Air • Touching clothing, food, silverware, or toothbrush • Drinking water that contains bacteria

21. Harmful Bacteria Human tooth with accumulation of bacterial plaque (smooth areas) and calcified tartar (rough areas)

22. Controlling Bacteria 3 ways to control bacteria: 1) Canning-the process of sealing food in airtight cans or jars after killing bacteria • endospores are killed during this process 2) Pasteurization-process of heating milk to kill harmful bacteria 3) Dehydration-removing water from food • Bacteria can’t grow when H2O is removed • example: uncooked noodles & cold cereal

23. Controlling Bacteria Antiseptic vs. Disinfectants Antiseptic- chemicals that kill bacteria on living things • means – “against infection” Examples: iodine, hydrogen peroxide, alcohol, soap, mouthwash Disinfectants- stronger chemicals that destroy bacteria on objects or nonliving things

24. Welcome to the world of viruses

25. General Structure of Viruses • Size range – • most <0.2 μm; requires electron microscope

27. General Structure of Viruses • Capsids • All viruses have capsids - protein coats that enclose and protect their nucleic acid • The capsid together with the nucleic acid are nucleocapsid • Some viruses have an external covering called envelope; those lacking an envelope are naked • Each capsid is constructed from identical subunits called capsomers made of protein

28. Structure of Virus

29. General Structure of Viruses • Two structural types: • Helical - continuous helix of capsomers forming a cylindrical nucleocapsid • Icosahedral - 20-sided with 12 corners • Vary in the number of capsomers • Each capsomer may be made of 1 or several proteins • Some are enveloped

30. Helical Nucleocapsids

32. General Structure of Viruses • Viral envelope • Mostly animal viruses • Acquired when the virus leaves the host cell • Exposed proteins on the outside of the envelope, called spikes, essential for attachment of the virus to the host cell

33. General Structure of Viruses • Complex viruses: atypical viruses • Poxviruses lack a typical capsid and are covered by a dense layer of lipoproteins • Some bacteriophages have a polyhedral nucleocapsid along with a helical tail and attachment fibers

34. Figure 6.9 Mickey Dufilho

35. Nucleic Acids • Viral genome – either DNA or RNA but never both • Carries genes necessary to invade host cell and redirect cell’s activity to make new viruses • Number of genes varies for each type of virus – few to hundreds Mickey Dufilho

36. Nucleic Acids • DNA viruses • Usually double stranded (ds) but may be single stranded (ss) • Circular or linear • RNA viruses • Usually single stranded, may be double stranded, may be segmented into separate RNA pieces

37. How Viruses Are Classified • Main criteria presently used are structure, chemical composition, and genetic makeup • Currently recognized: 3 orders, 63 families, and 263 genera of viruses • Family name ends in -viridae, i.e.Herpesviridae • Genus name ends in -virus, Simplexvirus • Herpes simplex virus I (HSV-I)

38. Mickey Dufilho

39. Mode of Viral Multiplication General phases in animal virus multiplication cycle: • Adsorption – binding of virus to specific molecule on host cell • Penetration – genome enters host cell • Uncoating – the viral nucleic acid is released from the capsid • Synthesis – viral components are produced • Assembly – new viral particles are constructed • Release – assembled viruses are released by budding (exocytosis) or cell lysis

40. Mickey Dufilho

41. Adsorption and Host Range • Virus coincidentally collides with a susceptible host cell and adsorbs specifically to receptor sites on the cell membrane • Spectrum of cells a virus can infect – host range • Hepatitis B – human liver cells • Poliovirus – primate intestinal and nerve cells • Rabies – various cells of many mammals

43. Penetration/Uncoating • Flexible cell membrane is penetrated by the whole virus or its nucleic acid by: • Endocytosis – entire virus is engulfed and enclosed in a vacuole or vesicle • Fusion – envelope merges directly with membrane resulting in nucleocapsid’s entry into cytoplasm

45. Replication and Protein Production • Varies depending on whether the virus is a DNA or RNA virus • DNA viruses generally are replicated and assembled in the nucleus • RNA viruses generally are replicated and assembled in the cytoplasm

46. Release • Assembled viruses leave host cell in one of two ways: • Budding – exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed • Lysis – nonenveloped and complex viruses released when cell dies and ruptures • Number of viruses released is variable • 3,000-4,000 released by poxvirus • >100,000 released by poliovirus

48. Damage to Host Cell Cytopathic effects - virus-induced damage to cells • Changes in size and shape • Cytoplasmic inclusion bodies • Inclusion bodies • Cells fuse to form multinucleated cells • Cell lysis • Alter DNA • Transform cells into cancerous cells Mickey Dufilho

49. Figure 6.16 Mickey Dufilho