VIRUSESCh. 2.1

Virus

• Virus = a small nonliving particle that invades and then reproduces inside a living cell

• Although viruses can multiply, they do so differently than other organisms. Viruses can multiply ONLY when they are inside a living cell.

How are viruses unlike living things?

• Biologists consider viruses to be nonliving because viruses are not cells. They do not use energy to grow and develop, or to respond to their surroundings.

Virus

• Host = a living thing that provides a source of energy for a virus

• Parasite = organisms that live on or in a host and cause harm to the host

Shapes and Sizes

• Virus shapes ….. Viruses vary in shape and size. They are very small and can only be seen with a specialized microscope.

• Bacteriophage = a virus that infects bacteria, “bacteria eater”

• Virus sizes …Viruses are so small they are measured in nanometers. One nanometer is one billionth of a meter. Viruses are 20 nm to over 200nm.

Names of Viruses

• Naming viruses = viruses are named after the disease they cause, for the organisms they infect, the place where it was first found, after people or the scientist who first identified the virus.

Virus Structure

• Virus structure = protein coat and inner core• Virus’s genetic material contains instructions

for making new viruses.• The proteins on the surface of a virus play an

important role during the invasion of a host cell.

• Each virus contains unique surface proteins.

Virus Structure

Lock and Key

• Explain the “lock and key” action of a virus =• Like keys, a virus’s proteins fit only into certain

locks or proteins on the surface of a host cell.

How do Viruses Multiply?

• 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.

Active and Hidden Viruses

• Active virus = Once entering a cell, the virus immediately goes into action.

• Hidden virus = Virus genetic material becomes part of the host cell. Later the virus becomes active and starts to reproduce and take over the host cell

Active and Hidden Virus

Viruses and the Living World

Viruses and disease • What are some diseases caused by viruses? Colds, AIDS, Apple Mosaic virus, rabies and distemper in dogs and cats

Usefulness of viruses • How are viruses good? Gene therapy for cystic fibrosis.

Viruses and the Living World

• How is a virus’s ability to get inside a host cell useful to scientists?

• Scientists add important genetic material to a virus. Then the virus enters a host cell and inserts that genetic material.