Viruses

Ch. 7.1

What is a Virus?• A virus is a tiny, NONLIVING particle that

invades and then multiply inside a living cell.• They do not have the characteristics of

organisms!

Characteristics of Viruses

• The only way in which viruses are like organisms is that they can multiply!

• Although viruses can multiply, they multiply differently than organisms.

• Viruses can only multiply when they are inside a living cell.

• No organisms are safe from viruses!• 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

feed off of another cell by harming it).• Most viruses destroy their hosts.

The Structure of Viruses

• Viruses are VERY SMALL!• Some are round. Others are shaped like rods,

bricks, threads, bullets or even robots!• A bacteriophage is a virus that attacks

bacteria. • Bacteriophage means “bacteria eater”.

• Although viruses may look different from one another, they all have similar structures.

• All viruses have two basic parts:– A protein coat– An inner core made of genetic material

• A virus’s genetic material contains the instructions for making new viruses.

• Some viruses even have a force-field called an outer membrane.

• The proteins on the surface of a virus play an important role during the invasion of a host cell.

• Each virus contains a unique surface proteins.

• The protein coat acts like a key and the cell is the lock.

• If the protein coat key fits the lock, it can invade the cell.

• Because they act like keys, viruses are very specific.

• That’s why the virus that makes you sick, doesn’t effect fish or dogs.

• Some viruses are even so specific they only attack your nose or throat.

• QUESTION:– What information does a virus’s genetic material

contain?

How Viruses Multiply

• Once inside a cell, a virus’s genetic material takes over many of the cells 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 a cell immediately, others lay low for a while.

Active Virus

• IMMEDIATLEY ATTACK!• 1. Enter the cell• 2. The Virus’s genetic material takes over the

cell’s functions.• 3. The cell quickly produces the viruses

proteins and genetic material.• 4. Then these parts assemble into new

viruses.

• It’s like a photocopy machine stuck in the “ON” mode. It just makes copy after copy after copy!

• 5. When the cell is full of new viruses, the host cell EXPLODES! Releasing hundreds of new Pirates! Ooops, I mean Viruses!

Hidden Viruses

• These guys lay low.• After a hidden virus enters a host cell, its

genetic material becomes part of the cell’s genetic material.

• The virus does not appear to affect the cell’s functions and may stay hidden for years.

• Then, all of a sudden…• It does a SNEAK ATTACK!• It takes over the cell’s functions in much the

same way that active viruses do.• The virus that causes cold soars is an

example of hidden viruses.• Then it goes back into hidden mode again.

QUESTION 2!!

• Where in a host cell does a hidden virus “hide” while it is inactive?