Download Interdependence

Viruses &
Diseases Objective 3
By Jennifer Carson & Debbie McElreath ~ John
Marshall High School
The student will demonstrate an understanding of the
interdependence of organisms and the environment.
Interdependence
Viruses and
organisms rely
on their
environment
and other
species for survival.
Viruses
Viruses are NOT cells. A virus
is an infectious agent made up
of:
•a core of nucleic acid (RNA or DNA)
•a protein coat
Alive or not?
Even scientists disagree as to
whether or not viruses are
alive. What do you think? Look
at the chart on the next page
to help you decide.
Characteristic
of life
CELL
VIRUS
Made of cells
YES
NO
Obtain & use
energy
YES
NO
Grow & develop
YES
Reproduce
YES
Respond &
adapt
Contain RNA or
DNA
Only inside a
living cell
Only inside a
living cell
YES
YES
YES
YES
Structure
of a virus
ENVELOPE
• Envelope (part of
the protein coat)
• Capsid (part of
the protein coat)
• Nucleic acid
(either DNA or
NUCLEIC
RNA)
ACID
CAPSID
Retrovirus
ENVELOPE
• A virus that
contains RNA
instead of DNA
• Human
RNA
Immunodeficiency
Virus (HIV) is a
retrovirus
• HIV causes AIDS
CAPSID
Bacteriophage
• A virus that
only infects
bacteria
CAPSID
HEAD
DNA
CAPSID
TAIL
FIBER
Ticking time
bombs . . .
Viruses do not reproduce,
EXCEPT inside a living cell.
They invade a living cell and
let the cell do the work for
them.
Lytic Cycle
The viral infection that
rapidly kills the host cell is
the lytic cycle.
Cycle Illustration
1
2
4
3
5
Lysogenic Cycle
The viral infection that enters
a cell, remains harmless for a
period of time (sometimes
years), and then becomes
harmful later is called the
lysogenic cycle.
Role of viruses
• All viruses act like parasites, harming
the host cell.
• Viruses cause disease in every kind of
organism—animals, plants, fungi,
protists, and bacteria.
Some viral diseases
•
•
•
•
•
HIV
Measles
Smallpox
Influenza
Chicken pox
•
•
•
•
•
Common cold
Herpes
Warts
Mononucleosis
Mumps
Viral diseases
usually cannot be cured,
but many can be prevented
by
•Good hygiene
•Immunization
MEASLES
SMALLPOX
HERPES
Links
http://www.virology.net/Big_Virology/BVFamilyIndex.html
Sources
http://www.virology.net/Big_Virology/BVFamilyIndex.html
Biology, Kenneth R. Miller & Joseph Levine, 1991, Prentice-Hall, Inc.,
Englewood Cliffs NJ.
Biology: The Web of Life, Eric Strauss & Marylin Lisowski, 1998,
Scott Foresman Addison Wesley, Menlo Park CA
TAKS Power Tools, Glencoe Science, Glencoe McGraw-Hill, 2001, New
York, NY.
Microsoft Office Clipart