Transcript Lesson 7: Viruses

Lesson 7: Viruses
What are viruses?
• Viruses: small, non-living, infectious particles
containing genetic material in the form of
DNA or RNA with a protein capsule, called
the capsid.
• Non-cellular particle
• Over 4000 viruses species classified but
scientists believe that there are millions
• Highly specific about what they invade
(ex: plant viruses infect only plant cells);
specialize in the cell types they infect.
Features of Viruses:
• Viruses have no cytoplasm
• Less than 0.1µm in diameter (100s of
thousands of viruses could fit inside a human
cell)
• Cannot grow or reproduce on their own
• Do not produce energy; do not create waste
• Take control of the cell that they infect
Viruses – Living or Non-Living?
• Considered non-living because:
– Do not metabolize energy
– Do not perform cellular respiration
– Cannot grow
– Cannot reproduce on their own (act as
parasites)
Shapes of Viruses
Viral Diseases
• Mild viral diseases such as the common
cold or chicken pox, or more severe viral
diseases such as AIDS or cholera, are all
infectious. They can spread quickly and
cause an epidemic (outbreak confined to a
geographical region) or a pandemic
(widespread, global epidemic).
Bacteriophages:
• Viruses infect single host species or a few
closely related hosts. Ex: human
immunodeficiency virus (HIV) infects
certain types of immune system cells.
• Viruses that infect bacteria are called
bacteriophages.
Vaccination
• Vaccinations are such preventions against viruses.
• Vaccines are mixtures that contain weakened
forms or parts of dangerous virus.
• When vaccines are injected into an individual’s
body, they trigger a response by the immune
system without causing an infection.
• This exposure creates a form of chemical
‘memory’ that allows the immune system to reach
quickly if the individual ever comes in contact
with the real virus.
Infectious Cycles
• Viruses must invade a living host cell to
reproduce
• There are two ways to do this
– 1. Lytic Cycle
– 2. Lysogenic Cycle
Homework:
• Why are viruses considered to be nonliving?
• What characteristics do viruses share with
all living things?
• Which viral diseases are quite common and
associated with the winter season?
• Explain the relationship between a virus’s
dormant period in a cell and the appearance
of cold sores.
Research:
• The human influence virus, H1N1 (2009swine flu), was declared a pandemic by the
World Health Organization (WHO). What
criteria does the WHO use to designate a
disease outbreak as ‘pandemic’? How many
deaths are thought to have resulted from this
pandemic? How many countries have
reported cases of H1N1? How did Canada
respond to this outbreak?
Research:
• Visit the WHO website and choose any
other viral disease and research its cause,
symptoms, prevention and treatment (if
any).
• WATCH:
http://www.khanacademy.org/video/viruses
?topic=biology