Download Bacteria and Viruses

VIRUSES
https://www.youtube.com/watch?v=UEKS4w9bfJg

Viruses are infectious agents with both living
and nonliving characteristics

1. Living characteristics of viruses
◦ a. They reproduce but only in living host cells
◦ b. They can mutate

2. Nonliving characteristics of viruses
◦ a. They contain no cytoplasm or cellular organelles
◦ b. They must replicate using the host cell's energy and
materials (Viruses don't grow and divide on their own)
◦ c. The vast majority of viruses possess either DNA or
RNA but not both.
Viruses
must invade healthy cells
in order to reproduce. They are
known as parasites.(They need
a host cell function)
Viruses that infect bacteria are
known as bacteriophages 


Viruses are composed
of two parts:
◦ A Protein Coat
◦ Inner core of genetic
material


The Inner Core of
nucleic acid is
surrounded by a protein
coat called a capsid
The Nucleic core is
either made up of DNA
or RNA but never both
How Viruses Multiply
VIRUSES CAN EXHIBIT TWO
TYPES OF LIFE CYCLES.
1. Active Viruses (Lytic Cycle)
2. Hidden Viruses (Lysogenic Cycle)
•SOME VIRUSES ARE ACTIVE ALL
THE TIME.
•SOME VIRUSES CAN BE HIDDEN
AND BECOME ACTIVE LATER.
•(See pages 212 and 213)
Active vs. Hidden Viruses
1 Attachment
Lambda phage
2 Entry
3 Prophage
in chromosome
Active Cycle
Hidden Virus
Cycle
6 Synthesis
8 Release
7 Assembly
5 Induction
Further cell
division
replications
4 Replication
of
chromosome
(and progeny)
cell division

http://www.youtube.com/watch?v=Rpj0emEGShQ&
feature=related
The Lytic (Active) and Lysogenic
(Hidden)
Cycles:
http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter17/animation_quiz_2.html
How HIV (a retro-virus) replicates and
causes AIDS
http://glencoe.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::550::400::/sites/dl/free/0078802849/383942/Retrovirus_Replication.swf::Retrovirus%20Replication
http://glencoe.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::550::400::/sites/dl/free/0078802849/592996/hiv.swf::HIV

Viruses are so small that most can only be seen
by the electron microscope ( 1935-tobacco
mosaic virus)

17-300 nanometers long (one millionth of
an inch) and about one thousand times
smaller than bacteria

can only grow in other cells (host cells)
Tobacco Mosaic Virus
Adenovirus
Each
virus is specific for the type of cell
(respiratory, intestinal, bacterial) that they
invade because the receptor sites on the
virus must match up with the receptor site
on the host cell (embedded in the plasma
membrane)
Example:

Rhinovirus (cold virus) will only
infect respiratory tissue




Some people think that viruses were
some of the first life forms
Other people think that they are
descendents of complex living organisms
but they dropped or lost their cell structure
Others think they arose from DNA that
escaped from cellular organisms
Some even think they came from aliens
(Mr. Kay)
What works against
viruses?
Vaccines
or immunizations
 By pre-infecting the body with small
 amounts of a particular virus, our body
can build up antibodies that will fight it for our
lifetime
Antibiotics DO NOT work against viruses
because they attack cell walls (which viruses
do not have)
*
Vaccine



Antigens (Dead/Weakened Viruses) are
deliberately introduced into the immune
system to produce immunity
Because the virus has been killed or
weakened, minimal symptoms occur
Have eradicated or severely limited several
diseases from the face of the Earth, such as
polio and smallpox
Viruses
Viruses enter body cells, hijack their organelles, and
turn the cell into a virus making-factory. The cell will
eventually burst, releasing thousands of viruses to
infect new cells.
Cell before infection…
…and after.
The Second Line of Defense
~Interferon~
-
Virus-infected body
cells release
interferon when an
invasion occurs
-
Interferon –
chemical that
interferes with the
ability to viruses to
attack other body
cells
What happens to already
infected cells?
White Blood Cells
~T-Cells~


T-Cells, often called
“natural killer” cells,
recognize infected
human cells and cancer
cells
T-cells will attack these
infected cells, quickly
kill them, and then
continue to search for
more cells to kill
The Third Line of Defense
~Antibodies~
-
-
Most infections never make
it past the first and second
levels of defense
Those that do trigger the
production and release of
antibodies
-
-
Proteins that latch onto,
damage, clump, and slow
foreign particles
Each antibody binds only to
one specific binding site,
known as an antigen
Vaccine



Antigens (Dead/Weakened Viruses) are deliberately
introduced into the immune system to produce
immunity
Because the virus has been killed or weakened,
minimal symptoms occur
Have eradicated or severely limited several diseases
from the face of the Earth, such as polio and
smallpox


Viruses grown on chicken embryos are
attenuated vaccines
Another type of vaccine is made by heat
killing the virus