Chapter 7

Viruses

What is a virus?

• Characteristics of Viruses– Virus is a tiny, nonliving particle that invades and then

multiplies inside a living cell– Viruses are not cells– They do not have the characteristics of organisms– They only way in which viruses are like organisms is that

they can multiply– Host is a living thing that provides a source of energy for

a virus or an organism– Parasites, are organisms that live on or in a host and

cause it harm

What is a virus?

• The structure of Viruses– Viruses are smaller than cells and vary in size and shape

(some are round, look like rods, bricks, etc.)– Bacteriophage is a virus that infects bacteria– 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– Lock-and-key– All viruses have two basic parts:

• A protein coat that protects the virus• An inner core made of genetic material

How Viruses Multiply

• Once inside a cell, a virus’s genetic material takes over many of the cells function. It instructs the cell to produce the virus’s proteins and genetic material. These proteins and genetic material then assemble into new viruses.

How Viruses Multiply

• Active Viruses– A virus attaches to the surface to a bacterium– The virus injects its genetic material into the bacterium– The virus’s genetic material takes over the cell functions

of the bacterium. The cell starts to produce the virus’s proteins and genetic material

– The proteins and genetic material assemble into new viruses that fill the bacterium.

– The bacterium bursts open, releasing new viruses. The viruses go on to infect more cells

How Viruses Multiply

• Hidden Viruses– A virus attaches to the surface of a bacterium– The virus injects its genetic material into the bacterium– The virus’s genetic material becomes part of a genetic

material of the bacterium– After some time, the virus’s genetic material removes

itself and becomes active– The cell begins to produce the virus’s proteins and

genetic material, which assemble into new viruses– The new viruses crowd the bacterium. Finally, the cell

bursts open and releases the new viruses

Viruses & Disease

• The spread of viral diseases– Viral diseases can be spread in various ways– Example: some can be spread through the contact

with a contaminated object, or through a bite of an infected animal

– Cold’s an flu viruses can travel in tiny drops of moisture that an infected person sneezes or coughs into the air

– Others can be spread only through contact with body fluids, such as blood

Viruses & Disease

• Treating Viral Diseases– There are NO cures for viral diseases– However, many over the counter medications can

help relieve the symptoms – The best treatment of a viral infection is bed rest– Resting, drinking plenty of fluids, and eating a well

balanced meal may be all you can do while you recover from a viral disease.

Viruses & Disease

• Preventing Viral Diseases– A vaccine is a substance introduced into the body to stimulate

the production of chemicals that destroy specific disease causing viruses and organisms

– A viral vaccine may be made from or altered, the viruses in the vaccine do no cause disease; instead they trigger the body’s natural defenses

– Another important way to protect against viral disease is to keep your body healthy• Eat nutritious food• Get enough sleep, fluids, and exercise• Washing your hands• Not sharing eating or drinking utensils