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VIRUSES I. Structure A. Viruses are particles containing: 1. Nucleic acid 2. Protein coat B. They can reproduce only by infecting living cells! All viruses enter living cells and use the infected cell to produce more viruses. C. A capsid is the virus’s protein coat D. Special proteins on the capsid “trick” the host cell to let the virus in Inside, virus genes get transcribed and translated into more viruses Host cell then bursts and is destroyed II. Types of Viruses • DNA viruses contain DNA nucleic acid • More stable and less prone to mutation • Respond well to vaccination • Ex: smallpox, chicken pox, herpes, HPV, Hepatitis B • RNA viruses contain RNA nucleic acid • Prone to mutations • Require frequent vaccination • Ex: Influenza, H1N1, Hepatitis C, HIV, Rabies, Rotavirus, Yellow Fever Examples of Viral Disease • Smallpox, the common cold, chickenpox, influenza, shingles, herpes, polio, rabies, ebola, hanta fever, and AIDS Different Hosts • Host cell is very specific • Animal hosts: rabies, HIV, chicken pox • Plant hosts: tobacco mosaic virus, carnation vein mottle potyvirus C. Viruses that infect bacteria are called bacteriophages III. Lytic Cycle 1) Virus injects nucleic acid into cell, taking over its metabolism 2) Virus proteins and nucleic acids assemble into complete viruses 3) Virus enzyme breaks cell membrane and wall, releasing new viruses that attack other Lysogenic Cycle 1. Virus injects its DNA into host cell 2. Viral DNA integrates into the host DNA 3. A host cell makes copies of the virus ever time it divides. The viral DNA embedded in the host’s DNA is called a prophage. V. Retroviruses A. Retroviruses contain RNA. Make a DNA copy FROM their RNA. Then this DNA is inserted into the DNA of the host cell. B. HIV (human immunodefiniciency virus) can lead to C. AIDS (acquired immunodefiniciency syndrome) VI. Defense A. Vaccination offers protection for uninfected individuals – Work by stimulating production of antibody forms memory cells without causing disease • Vaccines are made from killed or weakened strains that cause antibody production but not the disease B. What are antibodies? • Proteins that recognize invaders and block their effects • Flags invaders for death by white blood cells Are Viruses Living or Non-living? • They depend on living things • Most likely developed after living cells • First viruses may have evolved from genetic material of living cells • Cannot reproduce on their own