Viruses Pages 40A – 46A

What is a virus? A virus is a tiny, non-living particle that enters and then reproduces inside a living cell. No organism is safe from a virus. A virus multiplies only when inside another living cell. The host is the organism that provides a source of energy for the virus. The virus acts like a parasite—it destroys the cells in which it comes into contact with.

Viruses come in many shapes-bricks, threads, bullets and complex robot-like shapes. Bacteriophage –a virus that infects bacteria. Bacteriophage means “bacteria eater”.

Turn to page 42 A in your textbook Viruses are very, very, very, very, very, small. They are measured in nanometers. A nanometer is one billionth of a meter!!!! Lets look at the picture on page 42A. The smallest viruses are about 20nm in diameter. Viruses are very small even when compared to bacteria-they cannot be seen with our school microscopes.

Why don’t viruses have a binomial nomenclature scientific name? They are not considered living organisms so scientists do not give them traditional scientific names.

How are viruses named then? By the disease they cause (polio).--------------------------------- Or By the organism they attack (tobacco mosiac)---------------------------- By the scientists that discovered it (Epstein-Barr virus)--- By the area that they came from (West Nile)------------------------------------------------

Let’s clear up diameter –vs- circumference Our egg experiment came off the internet with the word diameter to measure. That would actually be only across the widest part of the egg, not around it. Hopefully you went around but that would be called…..

The circumference

The structure of a virus All viruses have two basic parts: a protein coat that protects the virus and an inner core made of genetic material. Some have an outer coating or envelope also. The proteins fit only certain “locks” on the surface of a host’s cell. It is called a lock and key action. See page 43A

So why is this lock and key thing important? It means that a virus can only attach to certain areas or cells of a host. For instance, most cold virus must hook onto cells in the nose and throat of humans. These throat and nose cells “compliment” or “fit” those on the virus. Like a key to a lock. See how the description fits?

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 take over immediately and others wait for awhile—10 days as incubation period. They hide and wait to come out.

What types of viruses are “hidden” The type that cause cold sores is one. While hidden there are no symptoms. When the virus becomes active the symptoms also show up. OUCH!

What causes the hidden virus to come out? Scientists believe it is stress or too much sunlight!?!?!?!?

Where does the virus hide? Generally in the nerve cells until it becomes activated again. 

Viruses and the Living World Some viral diseases are mild—such as a cold. Some viral diseases are not—AIDS Viruses can affect all living things-trees, people, animals, plants, bacteria.

There are some useful things about viruses. Using “gene therapy” scientists use the virus’ ability to enter a host cell. They add genetic material to the virus and use him as a “messenger service” One disease they have used this for is cystic fibrosis (lungs do not function properly). The gene therapy virus delivers needed genetic material to the impaired lung cells.

OK--Activity You are going to design a virus that can fit a cell’s surface—table work—no moving-thank you.  1. Remember the lock and key theory. 2. You may use 3 colors but do not waste paper. 3. Your virus must be able to fit your assigned cell surface. 4. Make up a name for your virus and it’s disease. 5. We will share with the class so do not waste any time—You have 10 minutes. GO!!