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I. What Is a Virus? II. Viral Structures A. DNA or RNA core B. Capsid III. Viral Infections A. Lytic B. Lysogenic IV. Viruses and Living Cells I. What is a virus? A. Particles of nucleic acid (DNA or RNA), protein, and in some cases, lipids. B. Viruses reproduce by infecting living cells and using the cell’s machinery to produce more viruses. C. Viruses are composed of core of DNA or RNA surrounded by a protein coat. II. Virus Structures-page 526 A. T4 Bacteriophage B. Tobacco Mosaic Virus Capsid proteins C. Influenza Virus Capsid RNA Tail sheath Tail fiber Surface proteins Membrane envelope III. Viral Infections A. Lytic infection occurs when a virus enters a host cell, the cell makes and assembles viral parts, and the new viruses leave by exocytosis or causing the cell to burst (lyse). B. Lysogenic infection occurs when a virus inserts its DNA into the DNA of the host cell, replicate with the host cell’s DNA, may remain dormant but is later activated and begins the lytic cycle Lytic vs. Lysogenic Cycle of Viruses III. Viral Infections Continued C. Prophage is viral DNA that is embedded in the host cell’s DNA. It may remain part of the host’s DNA for many generations before becoming active. Any number of factors can cause the prophage to activate. D. Retroviruses are viruses with RNA as their genetic material instead of DNA. Once they invade a host cell, they make a DNA copy of their RNA. This DNA copy is then inserted into the host cell DNA, much like a prophage would. E. Antibiotics won’t cure viral diseases! (The Doctor can’t cure your cold!) F. Vaccines can be given to help your own immune system fight the disease Some vaccines work by preventing viruses from attaching to cells, and thus injecting their DNA inside the host cell Vaccines for smallpox, a deadly virus, helped wipe it out. Other diseases that can be prevented by vaccines are: Common cold is caused by virus, but does not require vaccines G. HIV, the virus that causes Aids, infects Tcells. HIV (Human Immunodeficiency Virus) can hide for years in the nucleus of T-cells (white blood cells that help fight infection). People can have no symptoms, yet be spreading the disease to many partners. HIV then begins the Lytic cycle and T-cells begin to die. The patient eventually dies from another disease that the immune system can’t control because there are no T-cells to help fight infection. Polio Poliomyelitis is a communicable disease caused by viral infection and occurs through direct contact with infected secretions. Polio is found worldwide, but immunization has reduced the incidence. Clinical polio affects the central nervous system (brain and spinal cord). Disability is more common than death. https://health.google.com/health/ref/Poliomyelitis Influenza Influenza is a viral infection that attacks your respiratory system — your nose, throat and lungs. Influenza, commonly called the flu, is not the same as the stomach viruses that cause diarrhea and vomiting. http://www.mayoclinic.com/health/influenza/DS00081 Measles is an infectious disease caused by a virus. It spreads easily from person to person. The main symptom of measles is an itchy skin rash. The rash often starts on the head and moves down the body. http://www.nlm.nih.gov/medlineplus/measles.html Mumps is a contagious disease that leads to painful swelling of the salivary glands. The salivary glands produce saliva, a liquid that moistens food and helps you chew and swallow. https://health.google.com/health/ref/Mumps IV. Viruses and Living Cells Diseases Caused by Viruses Are Viruses Living? Based upon the characteristics of life- NO; but borderline of living and non-living Viruses are not made of cells-they’re particles of cells Viruses cannot reproduce WITHOUT infecting living cells Viruses do have some characteristics of life, especially after infecting cells. They can reproduce, regulate gene expression, and evolve.