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Viruses!
What is a virus?
A non-living particle composed of a protein
coat (capsid) & nucleic acids
The virus can have either DNA or RNA
(retrovirus) as its nucleic acid.
Different types of viruses
Top 10 reasons why virus aren’t
considered “living”…
#10
Viruses do not grow
#9
Viruses can’t reproduce without a host
#8
Viruses do not maintain homeostasis
#7
Viruses do not have metabolism or require
energy
#6
Viruses are not made of cells.
#5
Viruses mutate very quickly
#4
Viruses do not have any cell organelles
#3
Viruses need a host for everything
#2
Viruses are smaller than bacteria
#1
VIRUSES CAN NOT DO ANY OF THE
FUNCTIONS OF LIFE & ARE NOT MADE
OF CELLS!!
Viruses have 2 basic shapes
1) Icosahedron (has
20 triangular sides)
EX: HIV 
2) Helix – coiled spring
EX: ebola 
Other virus-like things
1) Viroids – smallest things that can
replicate, are pathogens. Made of small
piece of RNA without the capsid.
(cause plant diseases)
2) Prions – abnormal clumps of proteins,
are pathogens.
EX: “Mad cow disease”
How do viruses work?
They hijack the cell and use it to make more
viruses!
How do viruses reproduce?
1) Lytic cycle steps:
a) virus attaches to cell receptor site
b) injects its genetic material into cell.
c) cell begins reading the viral DNA and
makes more viruses.
d) the cell is destroyed & new viruses are
released to infect other cells
2) Lysogenic cycle steps:
a) Virus attaches to cell
b) Injects the virus DNA into the cell & the
DNA fuses with the cell’s DNA
c) Cell keeps functioning as normal & does
mitosis, each new cell will have the viral
DNA
d) Some signal starts the cells to making
the viruses and the cells will be
destroyed at one time.
Lytic & Lysogenic cycles
Viruses & diseases
Most viruses act on specific types of cells.
Plant viruses do not infect animals cells!
Keep in mind that viruses can MUTATE very
quickly to attack other types of cells
though!!!
Some diseases that are caused by
viruses…
Polio
HIV/AIDS
Flus
Measles
Mumps
Chickenpox
Smallpox
Hepatitis
Herpes
Ebola
Colds
How can viruses be treated or
prevented?
Prevention:
1) vaccines (deactivated viruses)
2) good hygiene
Treated:
1) symptoms can be treated
2) the body’s immune system will work on
the virus
Some viruses can be helpful
Bacteriophages (viruses that attack bacteria)
are used in research. We figured out that
DNA carries genetic info by using
bacteriophages!
Viruses can be used as VECTORS to carry
“good” genes into a cell
Bacteriophage
HIV
Herpes
Smallpox