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Chapter 19.2 & 19.3 Viruses & Diseases caused by bacteria and viruses http://www.cellsalive.com/howbig.htm 1 19-2 Viruses Virus = particle made up of nucleic acid, protein, and in some cases lipids that can replicate only by infecting living cells Vary in size and structure ALL viruses: enter living cells and, once inside, use the machinery of the infected cell to produce more viruses. A typical virus is composed of a core of DNA or RNA surrounded by a protein coat Some have a few genes to more than 100 genes Capsid = outer protein coat of a virus 2 3 capsid proteins of a typical virus bind to receptors on the surface of a cell and “trick” the cell into allowing it inside cell transcribes and translates the viral genetic information into viral capsid proteins. Sometimes that genetic program causes the host cell to make copies of the virus, and in the process the host cell is destroyed viruses are highly specific to the cells they infect 4 Viral Infection Once the virus is inside the host cell, two different processes may occur. 1. Some viruses replicate themselves immediately, killing the host cell. (Lytic) 2. Other viruses replicate themselves in a way that doesn't kill the host cell immediately. (Lysogenic) 5 6 Lytic Infection Ex: Bacteriophage T4 a virus enters a cell, makes copies of itself, and causes the cell to burst The host cell cannot tell the difference between its own DNA and the DNA of the virus. shuts down the infected host cell Virus uses material of host cell to make new viruses lyses cell and new viruses go to infect other cells 7 My E. coli has a Virus 8 9 Lysogenic Infection process by which a virus embeds its DNA into the DNA of the host cell and is replicated along with the host cell's DNA do not lyse the host cell right away; remains inactive for a period of time Prophage = the viral DNA that is embedded in the host cell's DNA 10 prophage may remain part of the DNA of the host cell for many generations before becoming active. Eventually, any one of a number of factors may activate the DNA of a prophage It will then remove itself from the host cell DNA and direct the synthesis of new virus particles. 11 12 Retroviruses virus that contains RNA as its genetic information (not DNA) produce a DNA copy of their RNA inserted into the DNA of the host cell may remain dormant for varying lengths of time Then become active and destroys host cell EX: HIV 13 Viruses and Living Cells Viruses must infect a living cell in order to grow and reproduce. take advantage of the host's respiration, nutrition, and all the other functions that occur in living things parasite!! 14 Are viruses alive?? 15 19–3 Diseases Caused by Bacteria and Viruses Pathogen = disease-causing agent Disease = a conflict between the pathogen and the host All viruses reproduce by infecting living cells, and disease results when the infection causes harm to the host. Disease results when bacteria interfere with the host's ability to obtain enough nutrients and energy to function properly. 16 Bacterial Disease in Humans growth of pathogenic bacteria = disrupts the body's equilibrium by interfering with its normal activities and producing disease. Bacteria produce disease in one of two general ways: Some bacteria damage the cells and tissues of the infected organism directly by breaking down the cells for food. Other bacteria release toxins (poisons) that travel throughout the body interfering with the normal activity of the host. 17 Using Cells for Food: Mycobacterium tuberculosis, lungs enter a blood vessel and travel to new sites in the body where it destroys more tissue. Releasing Toxins : Streptococcus (scarlet fever) Corynebacterium diphtheriae (throat – death) 18 19 Preventing Bacterial Disease Vaccine = a preparation of weakened or killed pathogens prompts the body to produce immunity to the disease Antibiotic = compound that blocks the growth and reproduction of bacteria Ex: penicillin and tetracycline 20 Bacterial Disease in Animals Bacillus anthracis (anthrax) Sheep, cows Makes spores can last for years Biological weapon? 21 Controlling Bacteria There are various methods used to control bacterial growth, including: Sterilization – extreme heat Disinfectants • Lead to resistant bacteria? Food storage and processing 22 Viral Disease in Humans Poliovirus - infects and kills cells of the nervous system Papillomavirus - infects cells in the outermost layer of the skin 23 24 Viral Disease in Animals disease – livestock Rous sarcoma virus foot-and-mouth Chickens Can cause cancer (oncogenic) 25 Viral Disease in Plants Viruses – hard time getting into plant cells Many spread by insects tobacco mosaic virus 26 Viroids and Prions Viroid = single-stranded RNA molecule that has no surrounding capsids Prion = infectious particle made up of protein rather than RNA or DNA scrapie - an infectious disease in sheep 27 More Prion diseases… Mad cow disease (Bovine Spongiform Encephalopathy) Creutzfeldt-Jakob Kuru 28