Transcript Viruses - Images

Viruses
I. What are viruses?
• A. non-living segments of
nucleic acids (DNA or
RNA) contained in a
protein coat.
• They reproduce by
invading other living cells.
•Comes from the Latin
word for “poison.”
•obligate intracellular
parasites.
Viruses:
• Do not grow.
• Have no homeostasis.
• Do not metabolize.
• They do cause disease in
many organisms… a
“pathogen.”
B. Structure:
• 1. Inner core- made of the
nucleic acid (DNA/RNA).
• 2. Capsid- a protein coat
that surrounds the inner
core.
• The arrangement of these
proteins determines the
shape of the virus.
• They do not have a
nucleus, cytoplasm, cell
membrane or organelles.
C. Types of Viruses:
• 1. Virulent- one that will
cause disease in a living
cell (host cell).
• 2. Temperate- one that
does not immediately
cause disease.
II. Virology
• The study of viruses.
• Scientists use
bacteriophages to study
viruses because they
reproduce so quickly.
Bacteriophages
•Are viruses that
infect bacteria as a
host cell.
III. Reproduction
•A. Lytic cycle
–reproductive
process for virulent
viruses.
B. Steps in the Lytic Cycle:
•1. Attachment
–bacteriophage attaches
its tail to a bacterial host
cell.
2. Entry
•Bacteriophage punches
a hole in the host cell
and injects its nucleic
acid into the host cell.
3. Replication
• The host cell’s DNA is
destroyed.
• The bacteriophage’s nucleic
acid takes over and controls
the production of proteins in
the host cell.
4. Assembly
• New viruses are made.
• The host cell fills with about
200 new viruses in about 90
minutes.
5. Lysis and Release
•The host cell will burst
open (lysis) releasing
the newly made viruses
free to attach and
invade other cells.
C. Lysogenic Cycle
•Reproductive process
for temperate viruses.
•Examples:
–HIV and
–Herpes Simplex I (cold-sore)
• 1. After viral DNA is injected
into the host cell, it
combines with the host cell’s
chromosomes and becomes
a provirus.
• It can be undetected for many
years.
• 2. The host cell divides by
mitosis and the provirus is
now in the daughter cells
(in a dormant state).
•3. Proviruses can “pop
out” of a cell at any
time, enter a lytic cycle
and cause disease.
IV. AIDS
• Acquired
• Immunodeficiency
• Syndrome
• caused by HIV.
Statistics
• The World Health
Organization estimated that
in 1998 5.8 million people
were newly infected with
HIV.
• Currently, it is estimated that
30 million people are infected
worldwide.
• Africa has the highest rate of
infection.
• Global Daily Death Toll – 8,000
• HIV is spread when body
fluids of an infected
person is passed on to an
uninfected person by
direct contact or
contaminated objects.
• 1. Sexual contact. (semen
and vaginal fluid)
• 2. Blood to blood contact.
• 3. Intravenous needles.
• 4. Breast milk.
• The average incubation period
may last 11 years before any
symptoms begin to appear.
• In some cases it has been
documented to last as long as
20 years.
V. Important Viral
Diseases:
• Chicken pox
• influenza
• rabies
• smallpox
• Hepatitis A and B
• common cold
• mumps and rubella