C H A P T E R 1 0 S E C T I O N 3

Viruses

Objectives

Explain how viruses are similar and different from living things

List the 4 main virus shapes

Describe the 2 kinds of viral reproduction

Quick Question…

Are viruses living?

What’s a virus??

A microscopic particle that gets inside a cell and often destroys the cell

Many viruses cause diseases

The common cold

The flu

AIDS

Size

Smaller than the smallest bacteria

About 5 billion virus particles could fit in a single drop of blood!

Viruses can change rapidly

Because they change so rapidly, we don’t know how many there are…they are difficult to fight

Are Viruses Living?

Like living things:

contain protein and genetic information

Not like living things:

Can’t eat

Can’t grow

can’t break down food

Can’t use oxygen

*Viruses cannot function on their own…

What is a virus???

Living or Not?

Viruses are not cells

No cytoplasm, no organelles

Can only reproduce only inside a host cell

Host: a living thing that a virus or parasite lives on or in Host cells are used as tiny factories; the virus forces the host to

make viruses rather than healthy cells!

Classifying Viruses

Grouped by:

Shape

Type of disease they cause

Their life cycle

Kind of genetic material they contain

Viruses

http://betterhealthnaturally.files.wordpress.com/2007/10/virus1.jpg

Shape

Crystals Ex: Polio

Cylinders Tobacco Mosaic Virus

Spheres Influenza

Spacecraft? T-4 Bacteriophage (attack bacteria!)

Polio

http://www.npspindia.org/images/Polio-Virus.jpg

Tobacco Mosaic Virus

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4b/graphics/C4b_TMV.GIF

Influenza Virus

http://www.chm.bris.ac.uk/webprojects2006/Kelly/influenzafigure1.jpg

http://www.news.wisc.edu/newsphotos/images/influenza_virus_Kawaoka04.jpg

T-4 Bacteriophage

http://oceanworld.tamu.edu/resources/oceanography-book/Images/BacteriophageCartoon.jpg

http://www.cbe21.com/subject/biology/photo/03060201/1341/T4%20bacteriophage2.jpg

Viral Structure

Made of genetic material inside a protein coat

Protein coat protects the genetic material & helps the virus enter the host cell

Some protein coats match the characteristics of the host’s

Viral Structure

Genetic material is either RNA or DNA

RNA is made up of one strand of nucleotides

DNA is made of 2 strands of nucleotides

RNA & DNA contain information about making proteins

Viruses that contain DNA: warts, chicken pox

Viruses that contain RNA: colds, flu, AIDS

A Destructive House Guest

Viruses attack living cells and turn them into virus factories

This cycle is called the LYTIC CYCLE

http://static.howstuffworks.com/gif/virus-human-lytic.gif

Steps of the Lytic Cycle

1. Virus joins itself to a host cell

2. Virus enters the cell or its genetic material is injected into the cell

3. Once the genes are inside, they take over the host cell and turn it into a virus factory

4. New viruses break out of the host cell, which kills the host. The cycle begins again…

A Time Bomb: Lysogenic Cycle

Some viruses don’t go straight into the Lytic Cycle

Genetic material is injected, but new viruses are not made right away

Genes stay inactive for a long time…when active the Lytic Cycle begins…

Treating a Virus

Antibiotics do NOT kill viruses

Antiviral medications do – stop viruses from reproducing

Prevention is the best cure

Childhood vaccinations help

Wash your hands, drink plenty of fluids…

Quick Quiz:

List 3 shapes of viruses and give an example of each

How are viruses like and unlike living things?