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?