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CHAPTER 20.1 - VIRUSES
PART 1 – VIRUS STRUCTURE AND FUNCTION
THE DISCOVERY OF VIRUSES
•Scientists were looking for the
cause of a disease that was
infecting
TOBACCO plants.
•Causing tobacco mosaic disease.
THE EXPERIMENT
•Filter a solution that
causes the disease
through a small filter
that bacteria cannot
get through.
THE RESULTS
•The filtered solution can still infect
the tobacco plant.
THE CONCLUSION
•The disease was
caused by
something
smaller than a
bacteria. They
called it a virus.
THE DISCOVERY
• 1935—Wendell Stanley
discovered the structure of a
virus and proved that they
are NOT a LIVING
ORGANISM.
1946 Nobel Prize
winner. Extensive
virus work..proved
that they cause
cancer.
WHAT IS A VIRUS
• Complex, submicroscopic, organic
particle. (20 nm, have carbon)
• Not cellular, no cell parts.
• Do not carry out life functions on their
own.
• Reproduce only inside a living cell
(host cell)
WHAT IS A VIRUS
•
•
•
Parasitic (live off others)
Disrupts the lives of the cells
they invade
Found in air, soil, and water
STRUCTURE OF A VIRUS
capsid
Nucleic acid
Tail
filaments
INFLUENZA
SMALL POX
BACTERIOPHAGE
EBOLA
WEST NILE
HIV
HEPATITIS C
STRUCTURE OF A VIRUS
• A virus is a particle made up of a nucleic
acid core (either DNA or RNA) and an outer
protein coat called a capsid.
• Some viruses also have an extra outer layer
called an envelope.
ROLE OF VIRUSES
• Most viruses are pathogens—disease
causing agents.
• Small pox, chicken pox, cold sores, warts,
AIDS, rabies, mumps, flu, measles, some
forms of cancer and the common cold are
caused by viruses.
HOW DOES THE BODY HANDLE
VIRUSES?
• It is the job of the immune system to fight
diseases in the body. Your skin is one of the
most important organs in this system because it
keeps pathogens out of your body.
• Once a virus is in your body, your main defense
white blood
is
cells. These cells are
specialized to fight pathogens.
• There are 2 main types of white blood cells. T
.B
cells and B cells
cells are normally more
important for fighting viruses. Once a virus
has entered your body, your B cells produce
proteins called antibodies that will remember
the virus and fight it off if the same virus
enters your body again. This means that you
normally never get the same viral infection
twice.
WHY DO PEOPLE HAVE MORE THAN
ONE COLD OR THE FLU MORE THAN
ONCE?
• These viruses mutate quickly so your
body doesn’t recognize them as the
same thing.
• (there are more than 200 strains of
the common cold)
VACCINE
•Substance prepared from
inactive or weak viruses that
cause your body to react and
produce antibodies without
making you sick.
THE HIV VIRUS
•HIV, the virus that causes AIDS, is
in a class of viruses called
retroviruses. These viruses have
RNA as their nucleic acid.
HOW DO RETROVIRUSES
REPRODUCE?
•They have a way to convert
RNA to DNA.
•The DNA is copied by the
cells they invade.
HIV’S STRUCTURE
HIV ATTACKS YOUR BODY’S T CELLS
VIRUS DOCKS BY MATCHING RECEPTOR
SHAPES ON HOST CELL SURFACE.
HIV
Matches the receptor on host
Host cell
BECAUSE HIV MUTATES VERY
QUICKLY, IT IS DIFFICULT TO
CURE.