Download Viruses and Bacteria

Viruses
and
Bacteria
© Amy Brown – Science Stuff
What is a virus?
Virus:
An infectious particle
that is nonliving.
The word virus comes
from the Latin word
poison
meaning “________”.
All viruses are parasites.
All viruses require a host.
Parasites:
Parasites live in or on other
living organisms, causing
them harm.
Host:
The host is the living
organism the parasite
lives on.
Martinus Beijerinck
Dutch Scientist
1898
Beijerinck is considered the
virology
founder of _________.
Virology is:
He was the first
to name these
very small
particles
“________”.
viruses
The study of viruses.
In 1898, he used
filtration
experiments to
prove that:
an agent
smaller than a
bacterium was
causing tobacco
mosaic disease.
Wendell Stanley
American biochemist
1904 - 1971
In 1935, Stanley
was able to isolate
crystals of the
tobacco mosaic
virus.
Stanley was
awarded the Nobel
Prize in chemistry.
Living organisms
do not crystallize,
so Stanley inferred
that viruses were
not “_____”.
alive
Characteristics of Viruses
extremely small
Viruses are _____________.
Most can be seen only with
electron microscope
an _________________.
A viruses is active only when
inside a living cell
______________.
When removed
from a living cell, it
_______ all
ceases
activities, but
retains its ability to
_____________.
infect the cell
They may be crystallized and stored
indefinitely, but even after longs
periods of time, they retain:
their ability to infect a living cell.
Viruses vary widely in terms of size and structure,
but they all have one thing in common:
They enter living cells and use the machinery of
the cell to produce more viruses.
Viruses are non-cellular.
1 – Head
2 – Capsid
3 – DNA or RNA
4 – Tail fibers
5 – Base plate
6 – Sheath
1. They are not made of cells and
have no cell parts.
2. Viruses consist of two parts:
DNA or RNA surrounded by a
protein coat.
3. Capsid –
The protein
coat that
surrounds
the DNA or
RNA .
The
Viral
Capsid
The capsid is made of
proteins
_______ that enable the
virus to enter a host cell.
The capsid has a particular
shape
_____ that must match
________
receptors on the surface of a
_________.
host cell
When the virus attaches to
these receptors, the cell is
“tricked” into:
letting the virus inside.
Viruses can reproduce, but
only _______________.
inside a living cell
They
reproduce
inside a cell by
getting the cell
to produce
viral parts
instead of cell
parts.
Since viruses must bind precisely to ________
proteins on the
cell
surface they are highly specific to the cells they
__________,
infect.
Viruses of eukaryotes are
Plant viruses can only usually tissue specific.
infect plant cells.
Example: Human cold
viruses infect only the cells
lining the upper respiratory
system, ignoring all other
tissues.
Animal viruses can only
infect animal cells.
Bacteriophages
are viruses that
infect only
certain types of
bacteria.
Viruses are not affected by any
known antibiotic
_______.
Anything that
will kill the
virus will also
kill the host.
Living Characteristics of Viruses:
1. They can reproduce--but only
inside a living cell.
2. They can mutate or change.
3. They have DNA or RNA.
Their genome may consist of
only four genes, or up to a
hundred genes.
Non-living Characteristics of Viruses:
1. They are non-cellular.
2. They have no metabolism.
They have no food or energy
requirements.
3. They can be crystallized and
dehydrated and stored
indefinitely. They come to
"life" only when injected inside
a living cell.
1. Since viruses have no enzymes
and no cell parts, they force the
host cell to:
start making viral parts
___________________.
2. A viral infection begins when:
the genetic material (DNA or
RNA) of a virus makes its way
into a host cell.
hijacks
3. Once inside, the virus _______
the cell, reprogramming the cell.
4. The viral genome takes over the
host cell and makes the host cell
________
viral parts
start producing _________.
5. The host cell will begin to make copies of the _________
viral DNA
protein capsids
and producing the ______________.
6. The host cell assembles the parts
into viruses.
7. The reproductive cycle ends with:
the exit of hundreds or thousands of
viruses from the infected host cell.
8. This often destroys
________ the host cell.
Each of these viral progeny has the
capacity to infect neighboring cells
thereby spreading the infection.
The Two Reproductive Possibilities:
1. Once a virus is inside a host cell, two
different processes may occur.
2. Some viruses replicate themselves
immediately, killing the host cell.
3. Other viruses replicate themselves in a way that
does not destroy the host cell.
4. These two processes
are called:
a) The lytic cycle
b) The lysogenic cycle
Now, let’s learn
the steps to the
lytic cycle!
In a lytic infection, a virus:
enters a cell, makes copies of itself,
and causes the cell to burst.
Bacteriophage T4 is an
example of a bacteriophage
that causes a lytic infection.
Attachment. Tail fibers
are used to attach to
receptor sites on the
surface of the host cell.
Release. The cell
swells, bursts, and
releases 100’s of new
viruses.
Assembly. The viral DNA or
RNA is assembled inside the
protein coat.
A phage that
reproduces only by a
lytic cycle is called a
virulent phage.
Entry. Phage DNA is
injected. Empty capsid
remains outside. Host
cell DNA is destroyed.
Synthesis. The
host cell is directed
to produce viral
genomes and
protein capsids.
1. In this type of viral reproduction:
the host cell makes copies of the viral genetic
material indefinitely.
2. The virus incorporates its DNA into the DNA of the
replicated along with
host cell. The viral DNA is then ________
the host cell’s own DNA.
kill the cell right away A
3. Lysogenic viruses do not __________________.
inactive for some
lysogenic virus may remain ________
period of time.
Phage attaches and
injects its DNA.
Daughter cell
with prophage
Many cell
divisions may
occur, producing
a large
population of
bacteria that are
infected with the
prophage.
Bacterial
chromosome
Bacteriophage
(phage)
The host
cell bursts,
releasing the
new viruses.
LYTIC
New viruses are produced.
LYSOGENIC
Certain features
determine whether:
Lytic cycle
is induced
Lysogenic cycle
Is entered
Bacterial cell divides by binary
fission normally. The viral
genome is copied and passed to
daughter cells.
Prophage
Viral DNA is
incorporated into the
bacterial chromosome,
forming a prophage.
Prophage:
The viral DNA
embedded into the
host cell’s DNA.
The prophage may remain part of the host
for many generations before becoming
__________________
active.
Eventually, certain environmental conditions
(chemicals, radiation) may trigger the switchover from
lysogenic cycle to the ____
lytic cycle.
the ________
Retroviruses have
RNA
____ as their
genetic information
DNA
rather than _____.
Retroviruse
s
• These viruses have an enzyme called
RNA template
__________________,
reverse transcriptase which transcribes their ____
DNA The newly made DNA then enters the
into ____.
___________
cell’s nucleusand integrates into the DNA of a chromosome.
• In this way, the retrovirus may remain dormant for some
length of time.
• It will eventually become ______,
active causing the host
cell to make ___________,
new viruses and causing the _____
death
of the host cell.
• Retroviruses are responsible for some types of
cancer.
• The AIDS virus is a retrovirus.
Comparison of Viruses and Cells
Have DNA or RNA
and a protein capsid
Cell membrane,
cytoplasm, nucleus,
cytoplasmic organelles
Only within a host cell
Reproduce independently,
either sexually or
asexually
DNA or RNA
None
No
DNA
Yes, in multicellular organisms
Yes
No
Yes
Yes
Yes
Viral Diseases
There is little that can be done to
cure a viral infection.
Antibiotics are effective against _______,
bacteria but not
against _______.
viruses
A few new drugs have been
developed that interfere
with the reproduction of the
virus, but they only seem to
slow the effect of the virus.
They do not provide a cure.
The battle against viral diseases lies in
the use of vaccines.
Vaccines:
Contain a harmless
variation of the
pathogen.
Our immune system launches a
response to the harmless form,
recognize it the
thereby learning to _________
next time that we are exposed
_______ to it.
When we are exposed to the
"real" pathogen, our immune
system can respond __________
much faster
learned to
since it has already _______
recognize the pathogen.
Colds
Hepatitis
AIDS
Flu
West Nile
Virus
Chicken pox