Ch. 7 Viruses

Key Terms 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.