1. Viruses and Bacteria Chapter 20 Coach Fults

2. Is a Virus Alive? All living things are made of cells, are able to grow, and reproduce, and are guided by information stored in their DNA The smallest organisms that have these properties are prokaryotes Viruses- are segments of nucleic acids contained in a protein coat

3. Is a Virus Alive? Most viruses, like Ebola can be seen with an electron microscope Viruses are pathogens- agents that cause disease. Viruses replicate by infecting cells using the cell to make more viruses Because viruses do not have all the properties of life, biologists do not consider them to be living They do not grow, no homeostasis, and do not metabolize

6. Discovery of Viruses Near the end of the 19 th century scientists were trying to find the cause of the tobacco mosaic disease, which stunts the growth of tobacco plants So they filtered sap taken from infected plant, and injected that injected that into healthy plants So they concluded that the pathogen was smaller than bacteria The pathogen was called a virus meaning “poison”

7. Discovery of Viruses In 1935, Wendell Stanley discovered that the organisms was a chemical not rather than an organism, and infact it was a crystal He concluded that the crystal was part RNA and part protein Later he separated the 2, then joined them back to create sick plants

8. Viral Structure The virus protein coat or capsid, may contain either RNA or DNA but not both RNA viruses- HIV, Flu, Rabies DNA viruses- Warts,Chickenpox,Mononucleosis Most viruses have an envelope covering the capsid The envelope helps the virus enter the cell- it is made of proteins, lipids, and glycoproteins Glycoproteins- are proteins with attached carbohydrate molecules that are derived from the host cell

9. Viral Structure Viruses come in many shapes Ebola virus is long and rod-like Influenza virus is spherical and studded with receptors These receptors help the virus enter the cells Tobacco mosaic virus is helical (corkscrew) Polyhedral virus contain around 20 triangular faces with 12 corners

10. Influenza

11. TMV

12. Viral Structure Viruses that infect bacteria are called bacteriophages A good example is the T4 bacteriophage

14. Viral Reproduction Viruses lack the enzymes necessary for metabolism and have no structures to make protein Therefore, they must rely on living host to reproduce To start reproduction a virus must enter a living cell TMV enters through tiny tears Animal virus by endocytosis Bacteriophage punches its way through a cell

15. Lytic Cycle In bacterial viruses, the cycle of viral infection, replication, and cell destruction is called the lytic cycle After the viral genes have entered the cell to replicate viral genes and to make viral proteins, such as capsids. The proteins are then assembled with replicated viral genes to form complete viruses The host cell then breaks open releasing new viruses

17. Lysogenic Cycle Sometimes viruses enter a host cell, but do not make new viruses Instead of producing virus particles, the viral gene is inserted into the host chromosome and is called a provirus Whenever the cell divides, the provirus also divides which results in 2 infected cells In this cycle, called lysogenic cycle, the viral genome replicated without destroying the host cell Sometimes if the environment changes a lysogenic cycle can begin the lytic cycle and destroys the cell

19. Lysogenic Cycle In animal cells, viruses can replicate slowly so that the host cell is not destroyed by the virus For example: Herpes Simplex 1 lives deep in the nerves of the face, and when conditions are right, such as fever or under stress, the virus begins to cause tissue damage that is seen as a cold sore

21. Host Cell Specificity Viruses are often restricted to certain hosts TMV infects plants but not animals Scientists hypothesize that this specificity may be due to the viruses’ origin Viruses may have originated when fragments of host genes escaped or were expelled from cells. The hypothesis that viruses originated from a variety of host cells may explain why there are so many different kinds of viruses

22. Structure of HIV- an Enveloped Virus The viral envelope is composed of a lipid bilayer derived from the membrane of the host cell On the surface glycoproteins cover the envelope In the envelope, the capsid which holds the viruses’ genetic material (which is 2 strands of RNA)

23. HIV

24. How HIV infects Cells 1 st - the virus attaches to the cell at specific sites called receptors 2 nd - attachment triggers endocytosis

25. Attachment The glycoproteins covering the envelope precisely fits a human cell surface receptor called CD4 So any cell that has CD4s are liable to bind to the virus In humans, the immune system cells called lymphocytes and macrophages, as well as certain cells in the brain, possess CD4 receptors

26. Entry Into Macrophages HIV cannot just enter a cell by docking onto a CD4 receptor. Rather, the glycoprotein must also activate a second co-receptor called CCR5 Ccr5 starts endocytosis; lymphocytes do not have CCR5 so HIV can’t enter it

27. Replication On the inside, HIV sheds its capsid The particle then releases an enzyme called reverse transcriptase Reverse transcriptase copies a naked viral RNA into a complimentary DNA version This process is mistake-proned, so this creates many new mutations Translation of the viral DNA by the host cell’s machinery directs the production of many copies of the virus

28. Replication HIV doesn’t rupture and destroy its host cell; instead it releases its new viruses by budding

31. AIDS Eventually and by chance over years, HIV’s surface glycoproteins change to a point that they now recognize a new cell surface receptor. This receptor is found on the subset of lymphocytes called T cells HIV reproduces in T cells and destroys them, this increases the number of viral particles in the blood, which infect other T cells In this destruction of T cells; the body no longer can fight off other diseases which signals the onset of AIDS

33. AIDS AIDS is a disease in which an individual is unable to defend his or her body against infections that do not normally occur in healthy individuals It takes years, for AIDS to develop, so infected people can infect many people without them knowing it It is transmitted through body fluids (spit, blood, sexual contact, sharing needles, to infants during pregnancy, or through breast milk)

34. Viral Diseases Flu Some viruses can cause cancer Hepatitis B- liver cancer Epstein-Barr virus- Burkitt’s lymphoma Human papilloma virus- cervical cancer

35. Emerging Viruses Virus that evolve in geographical isolated areas and are pathogenic are called merging viruses West Nile; probably came from a bird migrating to the US; which can be fatal especially in the elderly b/c it cause brain swelling Hantavirus in rodent dropping kill 38% of people that are infected

36. Prions and Viroids 1982, a new class of pathogens called prions were discovered Prions contain a protein with no nucleic acid Ex: mad cow disease ( cows eats food tainted with infected cows remains) Viroid- is a single strand of RNA that has no capsid Usually affect cash crops

38. Bacterial Structure 1. Internal Compartmentalization- lack a nucleus, compartments, and membrane systems 2. Cell Size- bacteria are about 1 micrometer; eukaryotes are 10 times that size 3. Multicellularity- all bacteria are single celled; if adhered their cytoplasm does not interconnect 4. Chromosomes- consist of a single circular piece of DNA 5. Reproduction- by binary fission, split in half 6. Flagella- singe protein that corkscrews; some eukaryotic cells have pili which are shorter flagella

39. Bacterial Structure 7. Metabolic Diversity- bacteria have aerobic respiration and anaerobic respiration

40. Bacterial Cell Shapes Bacillus- rod shaped Coccus- round shaped Spirillum- spiral shaped Strepto- chains Staphylo- clusters

44. Bacterial Cell Shapes Outside a peptoglycan cell wall many bacteria have a gel-like layer called a capsule Eubacteria can have 2 types of cell walls, distinguished by a dye staining technique called the Gram Stain. 1 group is called Gram-positive and the other Gram-negative Gram staining is important in medicine b/c the 2 groups of eubacteria differ in their susceptibility to different antibiotics

46. Bacterial Cell Shapes Antibiotics- are chemicals that interfere with the life process in bacteria Thus, gram staining can help determine which antibiotic would be most useful in fighting the infection Some bacteria form thick-walled endospores around their chromosome and a small bit of cytoplasm when they are exposed to harsh conditions Can de temp., lack of nutrients, drought; they can go dormant for years then release new bacteria

50. Bacterial Cell Shapes Pili allows bacteria to adhere to the surface of sources of nutrition, like human skin Some kinds of pili enable bacteria to exchange genetic information through a process called conjugation; this is the process in which pili from one bacteria adhere to another bacteria and swap genes

52. Photosynthesizers A significant fraction of he world’s photosynthesis is carried out by bacteria Photosynthetic bacteria can be classified in 4 major groups based on their pigment they contain; purple nonsulfur bacteria, green sulfur bacteria, purple sulfur bacteria, and cyanobacteria Green and Purple sulfur bacteria grow in anaerobic places; they can’t use water for electrons in photosynthesis so they use sulfur compounds like hydrogen sulfide

53. Photosynthesizers Cyanobacteria is thought to have created our atmosphere Ex: Anabaena

54. Chemoautotrophs These obtain energy by removing electrons from inorganic molecules such as ammonia, methane, and etc… Help in recycling nitrogen for plant usage Ex: Nitrobacter

56. Heterotrophs Most bacteria are heterotrophic Together with fungi heterotrophs are the principal decomposers of the living world Many are aerobic Rhizobium which lives on the roots soybeans, beans, peas, peanuts, alfalfa, and clover help put nitrogen back into soil after crop has been harvested

59. Pathogenic Bacteria Your body has a vast amount of different sources and bacteria can compete with your body for many of these resources which can make you ill

60. Bacteria can Metabolize Their Host Heterotrophic bacteria secrete and enzyme that breaks down complex molecules for the bacteria to absorb them Tuberculosis, a disease of the lungs, is caused by Mycobacterium tuberculosis, which could kill in 18 months

62. Important Bacterial Diseases Anthrax- inhalation of spores Bubonic plague- bite of infected flea Chloera- drinking contaminated water Dental Cavities- bacteria in mouth Lyme disease- bite of infected tick Typhus- bite of infected flea

63. Anthrax

64. Chloera

65. Lyme Disease

66. Typhus

67. Bubonic Plague