2 VirusesVirus – non-cellular particle made up of genetic material and protein. Reproduce only by infecting living cells.TMV – tobacco mosaic virus – first heavily studied virusDmitri Ivanovski – 1892, cause of TMV – juice extracted from infected plantsMartinus Beijerinck – 1897, named TMV particle virusesWendell Stanley – 1935, purified TMV into a crystal – viruses are not living things.
3 Virus Anatomy Many shapes possible Typical virus composed of a core of either DNA or RNA (not both), surrounded by an outer protein coat, or capsid. Capsid includes proteins that enable the virus to enter a host cell.
5 Viral Infection*Viruses attach with tail fibers and inject genetic material into host cell. Most viruses are highly specific to the cells they infect. Generally, they are species specific, but they may infect larger groups of organisms (rabies and mammals).- Bacteriophages – viruses which invade bacteria.
6 Lytic Infection Host cell lysed and destroyed – kills cells quickly! Ex. Cold, flu virusesVirus takes over cell and uses cell to make copies of itself
7 The Lytic Cycle Lytic Cycle Bacteriophage protein coat Bacteriophage DNABacterialchromosomeBacteriophage attaches to bacterium’s cell wallBacteriophage enzyme lyses thebacterium’s cell wall, releasingnew bacteriophage particles thatcan attack other cells.Lytic CycleBacteriophage injects DNA into bacteriumBacteriophage proteins and nucleic acids assemble into complete bacteriophage particlesBacteriophageBacteriophage DNABacteriophage proteinBacteriophage takes over bacterium’s metabolism, causing synthesis of new bacteriophage proteins and nucleic acids
8 Lysogenic InfectionDoes not lyse host cell right away – lies in wait and doesn’t kill cell quicklyEx. Herpes (cold sores), HIV virusesVirus embeds its DNA into DNA of host cell and is replicated along with the host cell’s DNA. Can lie dormant for years!
9 The Lysogenic Cycle Lytic Cycle Lysogenic Cycle Bacterial chromosome Bacteriophage DNABacteriophage injects DNA into bacteriumBacteriophage DNA (prophage) can exit the bacterial chromosomeLytic CycleLysogenic CycleBacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cellsBacteriophage DNA forms a circleBacteriophage DNA (prophage) may replicate with bacterium for many generationsProphageBacteriophage proteins and nucleic acids assemble into complete bacteriophage particlesBacteriophage DNA inserts itself into bacterial chromosome
11 Retroviruses Important group of viruses AIDS, contain RNA, once inside the cell, the RNA produces DNA which acts as a prophage and binds with the cell’s DNA.Virus may remain inactive for many years“Retro” means backward, RNA to DNA, may cause some forms of cancer and AIDS
12 Are Viruses Alive? Viruses are known as parasites Viruses are not cells and cannot reproduce independently. But, when infect living cells, can make copies of themselves, regulate gene expression, and even evolve.
13 Diseases Caused by Viruses Pathogens – disease producing agentsViruses – smallpox, polio, measles, AIDS, mumps, influenza, Yellow Fever, rabies, common cold.No cure, the only way to be healed is for your own immune system to produce antibodies to resist the virus. Antibiotics don’t work for viruses!Interferons – release by cells when they are attacked by a virus, might be a possible treatment.Cancer – oncogenic viruses cause cancer. Not all viruses cause cancer, not all cancers are caused by virus.Prevention is best protection – vaccinations – weak or killed virus
14 Common Diseases Caused by Viruses Type of VirusNucleic AcidDiseaseOncogenic virusesRetrovirusesAdenovirusesHerpesvirusesPoxvirusesDNARNAcancercancer, AIDSrespiratory infectionschickenpoxsmallpox
15 Diseases Caused by Bacteria Bacteria – diphtheria, tuberculosis, typhoid fever, tetanus, Hansen Disease, syphilis, cholera, bubonic plagueBacterial illnesses are caused by toxins produced as bacteria growBacterial disease can be treated with antibiotics and prevented with vaccinesBacteria are becoming resistant to antibiotics.
16 Similarities Between Bacterial and Viral Infections Modes of transmission similarThrough the air, in water, in food, in body fluids, animal bites/scratchesBoth cause diseases and can be deadlyBoth have ways of being preventedVaccines for both and good hygiene/sanitation prevents disease
17 Differences Between Bacterial and Viral Infections Antibiotics only treat BACTERIAL infections! They do NOT work on viral infections.Viral infections are treated by the body’s immune systemBacteria are living cells who poison or “eat” our own cells.Viral cells inject genetic material into our own cells and use our own cells against our body