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Ch. 7 Viruses Key Terms 1. 2. 3. 4. 5. Virus Host Parasite Bacteriophage Vaccine What is a Virus • Virus is a tiny, nonliving particle that invades and then multiplies inside a living cell. • Viruses are not cells. • The only way in which viruses are like organisms is that they can multiply. • They can only multiply when they are inside a living cell. What is a Virus • The organism that a virus multiplies inside is called a host. • A host is a living thing that provides a source of energy for a virus or an organism. • Viruses act like parasites. (organisms that live on or in a host and cause it harm). Structure of Viruses • Viruses are smaller than cells and vary in size and shape. • Some are round • Others are shaped liked rods, brinks, threads, or bullets. Bacteriophage “bacteria eater”: is a virus that infects bacteria. Structure of Viruses • All viruses have two basic parts: a protein coat that protects the virus and an inner core made of genetic material. • Surface proteins play a huge role in the invasion of a cell. • Shape allows it to attach to certain cells in the host. • Most can only attach to a certain type of cell. (lock and key type situation) • A cold virus can only attach to cells in the nose and throat. How viruses multiply • Once inside a cell, a virus’s genetic material takes over many of the cell’s functions. • It instructs the cell to produce the virus’s proteins and genetic material. • These proteins and genetic material then assemble into new viruses. • Some viruses take over cell functions immediately, others wait for awhile. Active Viruses • After entering a cell, an active virus goes into action immediately. • It’s genetic material takes over and quickly begins to produce the virus’s proteins and genetic material. • New viruses are made. (photocopy) • Once the invaded cell is full of viruses it burst open and releases hundreds of new viruses as it dies. Hidden Viruses • Some viruses are hidden inside of the cell and are not active. (Sometimes for very long periods of time). • Certain conditions can cause the virus to become active. • A cold sore is an example. • Sunlight or stress can cause people to develop cold sores. • Where in a host cell does a hidden virus “hide” while it is inactive? Genetic Material Viral Diseases Viruses can cause diseases. (Cold, flue, AIDS, etc) They can spread in various ways. (contact with contaminated objects, a bite from an infected animal) Treatment for viral diseases. (no cures for them) Medicine can relieve the symptoms of a viral infection. Resting, drinking plenty of fluids, and eating well balanced meals can help you recover from a viral disease. Vaccines are used to prevent diseases.