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Viruses
and
Bacteria
What is a virus?
Virus: An infectious particle
that is nonliving.
The word virus comes
from the Latin word
meaning “________”. poison
All viruses are parasites.
All viruses require a host.
Parasites live in or on other
living organisms, causing
them harm.
Parasites:
Host:
The host is the living
organism the parasite
lives on.
Martinus Beijerinck
Dutch Scientist
1898
Beijerinck is considered the
founder of _________.
Virology is:
The study of viruses.
virology
In 1898, he used
filtration
experiments to
prove that:
an agent
smaller than a
bacterium was
causing tobacco
mosaic disease.
He was the first
to name these
very small
particles
“________”. viruses
Wendell Stanley
American biochemist
1904 - 1971
In 1935, Stanley
was able to isolate
crystals of the
tobacco mosaic
virus.
Living organisms
do not crystallize,
so Stanley inferred
that viruses were
not “_____”. alive
Stanley was
awarded the Nobel
Prize in chemistry.
Characteristics of VirusesViruses are _____________.
Most can be seen only with
an _________________.
extremely small
electron microscope
A viruses is active only when
______________. inside a living cell
When removed
from a living cell, it
_______ all
activities, but
retains its ability to
_____________.
ceases
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
_______ that enable the
virus to enter a host cell.
proteins
The capsid has a particular
_____ that must match
________ on the surface of a
_________.
shape
receptors
host cell
When the virus attaches to
these receptors, the cell is
“tricked” into:
letting the virus inside.
Viruses can reproduce, but
only _______________.
They
reproduce
inside a cell by
getting the cell
to produce
viral parts
instead of cell
parts.
inside a living cell
Since viruses must bind precisely to ________ on the
__________, they are highly specific to the cells they
infect.
proteinscell surface
Plant viruses can only
infect plant cells.
Animal viruses can only
infect animal cells.
Viruses of eukaryotes are
usually tissue specific.
Example: Human cold
viruses infect only the cells
lining the upper respiratory
system, ignoring all other
tissues.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:
___________________.
2. A viral infection begins when:
the genetic material (DNA or
RNA) of a virus makes its way
into a host cell.
3. Once inside, the virus _______
the cell, reprogramming the cell.
start making viral parts
hijacks
4. The viral genome takes over the
________ and makes the host cell
start producing _________.
host cell
viral parts
5. The host cell will begin to make copies of the _________
and producing the ______________.
viral DNAprotein capsids
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 ________ the host cell.
Each of these viral progeny has the
capacity to infect neighboring cells
thereby spreading the infection.
destroys
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
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.
Now, let’s learn
the steps to the
lytic cycle!
Attachment. Tail fibers
are used to attach to
receptor sites on the
surface of the host cell.
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.Assembly. The viral DNA or
RNA is assembled inside the
protein coat.
Release. The cell
swells, bursts, and
releases 100’s of new
viruses.
A phage that
reproduces only by a
lytic cycle is called a
virulent phage.
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
host cell. The viral DNA is then ________ along with
the host cell’s own DNA.
3. Lysogenic viruses do not __________________. A
lysogenic virus may remain ________ for some
period of time.
replicated
kill the cell right away
inactive
Bacteriophage
(phage)
Phage attaches and
injects its DNA.
Bacterial
chromosome
Certain features
determine whether:
Lytic cycle
is induced
Lysogenic cycle
Is entered
LYSOGENICLYTIC
Viral DNA is
incorporated into the
bacterial chromosome,
forming a prophage.
Prophage
Bacterial cell divides by binary
fission normally. The viral
genome is copied and passed to
daughter cells.
Many cell
divisions may
occur, producing
a large
population of
bacteria that are
infected with the
prophage.
Daughter cell
with prophage
New viruses are produced.
The host
cell bursts,
releasing the
new viruses.
Prophage:The viral DNA
embedded into the
host cell’s DNA.
The prophage may remain part of the host
__________________ before becoming
active.
for many generations
Eventually, certain environmental conditions
(chemicals, radiation) may trigger the switchover from
the ________ cycle to the ____ cycle.lysogenic lytic
Retroviruses
Retroviruses have
____ as their
genetic information
rather than _____. DNA
RNA
• These viruses have an enzyme called
__________________, which transcribes their ____ template
into ____. The newly made DNA then enters the
___________ and integrates into the DNA of a chromosome.
• In this way, the retrovirus may remain dormant for some
length of time.
• It will eventually become ______, causing the host
cell to make ___________, and causing the _____
of the host cell.
• Retroviruses are responsible for some types of
cancer.
• The AIDS virus is a retrovirus.
reverse transcriptase RNA
DNA
cell’s nucleus
active
new viruses death
Comparison of Viruses and Cells
Have DNA or RNA
and a protein capsid
Only within a host cell
Cell membrane,
cytoplasm, nucleus,
cytoplasmic organelles
Reproduce independently,
either sexually or
asexually
DNA or RNA
None
No
No
Yes
DNA
Yes, in multicellular organisms
Yes
Yes
Yes
Viral Diseases
There is little that can be done to
cure a viral infection.
Antibiotics are effective against _______, but not
against _______.
bacteria
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,
thereby learning to _________ it the
next time that we are _______ to it.
recognize
exposed
When we are exposed to the
"real" pathogen, our immune
system can respond __________
since it has already _______ to
recognize the pathogen.
much fasterlearned
Colds
Hepatitis
Flu
AIDS
Chicken poxWest Nile
Virus
1. They are known for their extreme ________ and small_____.
2. They are much smaller than a _____.
3.They consist of ___________________________, but they
have no __________. They are tiny molecules of
_________________.
4.They have only been identified in plants. But, they are
suspected of causing some diseases in animals for which no
pathogen has ever been isolated.
5.The important lesson we have learned from viroids is that:
a molecule can be an infectious agent and cause
disease.
simplicity
virus
small, circular molecules of RNAprotein coat
naked circular RNA
size
1. These are disease-causing particles that:
do not contain DNA or RNA.
2. They are tiny bits of _______.
3. Prions cause degenerative brain diseases such as
_______________.
4. How can a protein, which cannot replicate itself, be a
pathogen?
The leading hypothesis is that a prion is a
______________________ normally present in brain
cells. When a prion enters a cell that contains the
normal form of the protein, the prion converts the normal
protein to the prion version.
protein
Mad Cow Disease
misfolded form of a protein
The Bacteria
The bacteria are
___________.prokaryotes
A prokaryotic cell:
does not have a
true nucleus or
membrane-bound
organelles.
Prokaryotes dominate the
biosphere. Their collective
biomass outweighs all
eukaryotes combined by at least
10 fold.
cholera
Some are _______ and cause
diseases, but most bacteria are
________________. A
relatively small number of
species cause _______.
harmful
benign or beneficial
disease
They are successful because
of their rapid cell division
(reproduction) and their great
metabolic diversity. They can
double their numbers every
___________ and live in
environments that:
support no other forms of life.
20 minutes
Domain:
Archaea
Kingdom:
Archaebacteria
Domain:
Bacteria
Kingdom:
Eubacteria
Classification of Prokaryotes
Strep
Archaea
The bacteria are separated into two different _______:domains
These are the “true” bacteria.
There is great variety in the organisms that belong to this kingdom. These bacteria are found in every environmenton Earth.
The eubacteria have a cell wall that contains a polysaccharidecalled peptidoglycan.
Eubacteria
Archaebacteria1. Under a microscope,
Archaebacteria look very
_______ to the eubacteria.
They are:
equally small, lack nuclei, and
have cell walls.
2. Chemically, the Archaebacteria
are ____________.
3. The Archaebacteria lack the
_____________ found in the
eubacteria. They also have
different _______________.
4. The Archaebacteria live in:
extremely harsh environments.
similar
very different
peptidoglycans
membrane lipids
Suitable temperature: 80-100 °F.
Moisture
Suitable food source
Darkness
Space to grow
Bacteria are found almost everywhere. The
best environment for growth has:
Bacteria are very large in
comparison to a virus.
Prokaryotes are identified by
several characteristics:
1. Shape
2.The materials composing
the cell wall
3. The way they move
4.The way they obtain
energy
Bacteria exist in three basic shapes:
1. Cocci are
spherical.
2. Bacilli are
rod-shaped.
3. Spirilla are
spiral
shaped.
Movement
Some bacteria are ______ and
others do not move at all.
Some move by means of
_______, whip-like structures
used for movement.
motile
flagella
Some lash or snake forward.
Others glide slowly over a layer
of slime they secrete.
Most bacteria are ________.
Some are ________________________.
harmless
pathogenic (cause diseases)
Soil
bacteria
Label the structures seen in the prokaryotic cell:
1 – cell wall
2 – cell membrane
3 – peptidoglycans
4 – flagella
5 – pili
6 – single, circular
chromosome
(DNA)
7 – ribosomes
The cytoplasm does not contain any…
…..membrane bound organelles.
The chromosome consists of ….
…..one single, circular, continuous molecule of DNA.
The cytoplasm is filled with many _________.ribosomes
A ________ may be present
outside of the ________. It is
composed of a gluey
_____________.
It enables prokaryotes to
adhere to their:
substrate or to other
individuals in the colony.
Some capsules protect
against __________. Some
capsules shield pathogenic
bacteria from:
attacks by their host’s
immune system.
capsulecell wall
polysaccharide
dehydration
Flagella: long whip like structure
used for movement.
Pili are shorter and thinner than
flagella. Pili serve to attach
bacteria to:
1)a food source
2)the surface of a liquid
3)another bacteria during
reproduction.
How Do Bacteria Obtain
Energy?
Most bacteria are ___________.
They do not have the ability to
_________________.
The heterotrophic bacteria are
further divided into….
….saprophytes and parasites.
heterotrophs
make their own food
Saprophytes:
a.Saprophytes live on dead organic matter.
b.Saprophytes are very important as
decomposers.Parasites:
a.A parasite is an
organism that invades
plants and animals and
lives off of them.
b.Host: The organism
that the parasite is living
off of.
A few bacteria are __________. They have
the ability to __________________.
autotrophsmake their own food
Photoautotrophs:
Photosynthetic organisms that use light energy from
the sun to convert carbon dioxide and water into the
organic molecule glucose, and oxygen.
Chemoautotrophs:
Use the energy from inorganic
reactions as a source of energy
to build molecules of glucose.
Growth and ReproductionIf conditions are favorable for growth,
bacteria can grow and divide at incredible
rates.
Many bacteria can divide every
__________ (under ideal conditions).
If reproduction continued unchecked at
this rate, a single prokaryotic cell could
give rise to a colony….
….outweighing Earth in three days.
20 minutes
In reality, prokaryotic reproduction is limited by:
a) the eventual exhausting of food supply
b) being poisoned by their own metabolic waste
c) competition from other microbes
d) being consumed by other organisms
Binary fission is a
type of asexual
reproduction where:
one cell undergoes
cell division to form
two cells.
When the bacterium
has grown to nearly
double its size:
it replicates its DNA
and divides in half.
Two identical
daughter cells
are formed.
During conjugation, a _____________
forms between two bacterial cells.
hollow bridge
Through this tube,
genes move from
one cell to the other.
There is no increase in numbers;
but they have redistributed the
_________________. The
transfer of genetic information
increases ______________ in
future populations.
Now they can go back to binary
fission and increase their
numbers.
genetic information
genetic diversity
Endospore FormationWhen conditions for growth become
__________, many bacteria form
structures called __________.
unfavorable
endospores
An endospore is formed ____________.
The contents of the _________ draw up
together and a ________ is formed
around it.
inside of a cell
cytoplasm
thick wall
These endospores can….
….survive extreme dryness, heat or cold.
They can remain _______ for months or
years while waiting for favorable growth
conditions to return.
dormant
The Importance of Bacteria
Bacteria are vital to
maintaining the living world.
The prokaryotes can easily
survive without the
__________, but the
eukaryotes are totally
dependent on the
___________.
eukaryotes
prokaryotes
Bacteria
Are
Decomposers
All living things
depend upon a
constant supply of:
carbon, nitrogen,
and other essential
elements. These essential
elements must
be recycled
when an
organism dies.
Bacteria are ___________
that help to _______ these
essential chemical elements.
decomposers
recycle
When an organism
dies, it is attacked
by bacteria and
broken down into
simpler materials.
Nitrogen
Fixation
Plants and animals must
have ________ to build
___________. Amino
acids are needed to build
________.
nitrogen
amino acids
proteins
Nitrogen gas makes up about 80% of Earth’s atmosphere, but….
….plants and animals are not capable of using nitrogen gas directly.
In a process called ______________,
bacteria are able to convert
____________________, a form that
plants can use.
nitrogen fixation
nitrogen gas into nitrates
Plants take up these ______
through their ______ and use
them to build ____________.
nitrates
rootsplant proteins
Animals eat the plants, and convert the
_____ proteins into _______ proteins.plant animal
When an organism dies, bacteria __________
the organism, returning this nitrogen to the
__________ to be used again.
decompose
ecosystem
Human Uses For Bacteria
Bacteria are used to
produce a wide variety of:
foods and beverages.
Examples: sour cream,
yogurt, cheese.
Some bacteria can
digest oil and are
helpful in cleaning up
oil spills.
Bacterial Diseases in Humans
Some bacteria are _________.
A pathogen is a disease-causing agent.
pathogens
Bacteria produce diseases in one
of two ways:
Some bacteria:
damage the
cells and tissues
by breaking
down the cells
for food.
Other bacteria:
release toxins
or poisons in
the body of the
host.
Many of the
diseases caused
by bacteria can
be prevented
with the use of
vaccines.
Vaccine:
A weakened or killed form of the
pathogen that stimulates the body’s
immune system to produce antibodies.
Once the body has “learned”to make the correct antibody,
the body will be able to
respond rapidly if infected
with the living, active form of
the pathogen.This rapid response of
the immune system is
called ________.immunity
AntibioticsAntibiotics are
compounds that:
kill bacteria.
They are effective
against _______,
but have no affect
on ______.
bacteria
viruses
Symbiotic Relationships between Organisms
Symbiosis is a _________________ association
between organisms of different species.
There are three types of symbiotic relationships:
• Mutualism
• Commensalism
•Parasitism
close and permanent
Mutualism:
The relationship
is beneficial
to both species.
Commensalism:
A relationship in which one
species benefits from the
association while the other is neither harmed
nor helped.
Parasitism:
A relationship in which one
species benefits and the other is
harmed.
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