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Virus and Bacteria Notes
• Bacteria are grouped into two kingdoms:
-Eubacteria and Arcahebacteria
• -Eubacteria and Archaebacteria have different
membrane lipids and archaebacteria lack the
peptidoglycan found in eubacteria cell walls.
• -Archaebacterial genes are more like those of
eukaryotes than those of eubacteria.
Bacteria are Prokaryotes and have:
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-Cell Wall
-Cell Membrane
-NO nucleus
-Ribosomes
-NO organelles
-Flagella (for
mobile species)
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Bacteria come in three shapes:
Bacillus- rod shaped bacteria.
Cocci- spherical shaped bacteria.
Spirilla- spiral/corkscrew shaped
bacteria
Metabolic Diversity
• Some bacteria are heterotrophs. They
are referred to as chemoheterotrophs.
• As bacteria take in organic molecules
for both energy and a supply of carbon.
• Some bacteria are autotrophs. They
are photoautotrophs if they use light
energy to convert CO2 and water to
carbon compounds. These are often
found near surfaces of lakes, streams,
and oceans.
• Chemoautotrophs can perform
chemosynthesis that perform the same
task as photoautotrophs except they do
not need to use light. They rely on
chemical reactions instead. Many are
found at hydrothermal vents.
Releasing Energy
• Obligate aerobes- require a constant
supply of oxygen
• Obligate anaerobes- must live in the
absence of oxygen
• Facultative anaerobes- Can function with
or without oxygen.
Growth
• _Binary_ Fission is when a bacteria divides in
half producing identical cells. This is asexual
and much simpler than mitosis.
• _Conjugation__- Some bacteria can exchange
genetic information this way when a hollow
bridge forms between two bacteria cells and
genes move from once cell to the other.
SPORE Formation- In unfavorable conditions,
bacteria can form spores that can remain
dormant for months while conditions improve.
Then the bacteria can germinate and grow
again.
Bacteria in the World
Decomposers - Bacteria can help the
ecosystem by breaking down dead tissue.
Very important also in sewage treatments!
Nitrogen Fixers- Bacteria can live in the
nodules of plant roots and fix nitrogen
(nitrogen fixation) which is critical in the
nitrogen cycle.
-Bacteria are also found in our intestines!
They make vitamins that the body cannot
produce by itself and we supply the bacteria
with a warm and safe home. This is a mutual
symbiotic relationship!
• Bacteria can also cause disease in
animals and plants.
• -Bacteria can do this by damaging cells
ant tissues directly.
• -Or bacteria can release toxins that
travel throughout the body and
interfere with the normal activity of the
host.
http://www.nwlincs.org/mtlincs/pilot
project/science/lsvirusbacteria.htm
VIRUSES
I. Virus Characteristics
-Viruses are not considered alive as they do
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not have a metabolism or reproduce on
their own.
-Viruses are composed of DNA or RNA
surrounded by a protein coat called a
capsid.
-If viruses are composed of RNA as
their genetic material, they are called
retroviruses
Are Viruses Living or
Non-living?
• Viruses are both and neither
• They have some properties of life
but not others
• For example, viruses can be killed,
even crystallized like table salt
• However, they can’t maintain a
constant internal state (homeostasis).
What are Viruses?
• A virus is a noncellular particle
made up of genetic
material and
protein that can
invade living cells.
II. Types of Viruses
A. Bacteriophages
•Viruses that attack
bacteria are called
bacteriophage or just
phage
•T-phages are a specific
class of bacteriophages
with icosahedral heads,
double-stranded DNA,
and tails
T-phages
•The most commonly studied
T-phages are T4 and T7
•They infect E. coli , an
intestinal bacteria
•Six small spikes at the base of
a contractile tail are used to
attach to the host cell
•Inject viral DNA into cell
Diagram of T-4
Bacteriophage
•Head with 20
triangular surfaces
•Capsid contains
DNA
•Head & tail fibers
made of protein
B. Retroviruses
Characteristics of Retroviruses
•Contain RNA, not DNA
•Contain enzyme called Reverse
Transcriptase
•When a retrovirus infects a cell, it
injects its RNA and reverse
transcriptase enzyme into the
cytoplasm of that cell
ENZYME
Retroviruses
cont…
•HIV, the AIDS
virus, is a
retrovirus
•Feline Leukemia
Virus is also a
retrovirus
C. Viroids &
Prions
1.Viroids
•Small, circular RNA
molecules without a
protein coat
•Infect plants
•Potato famine in
Ireland
•Resemble introns
cut out of eukaryotic
2. Prions
•Prions are “infectious
proteins”
• They are normal body
proteins that get converted
into an alternate configuration
by contact with other prion
protein involved in human
and mammalian prion proteins
• They have no DNA or RNA
•The main diseases is called
“PrP”
Prions cont….
•Prions form insoluble
deposits in the brain
•Causes neurons to rapidly
degeneration.
Ex. Mad cow disease (bovine
spongiform encephalitis:
BSE) is an example
•People in New Guinea used
to suffer from kuru, which
they got from eating the
brains of their enemies
III Viral
History
Discovery of Viruses
•Beijerinck (1897)
coined the Latin name
“virus” meaning poison
•He studied filtered plant
juices & found they
caused healthy
•plants to become sick
Tobacco Mosaic Virus
•Wendell Stanley
(1935) crystallized
sap from sick
tobacco plants
•He discovered
viruses were made of
nucleic acid and
protein
Smallpox
•Edward Jenner (1796)
developed a smallpox
vaccine using milder
cowpox viruses
•Deadly viruses are
said to be virulent
•Smallpox has been
eradicated in the
world today
IV. SIZE of Viruses
•Viruses are smaller
than the smallest cell
•Measured in
nanometers
•Viruses couldn’t be
seen until the electron
microscope was
invented in the 20th
century
V.Viral Reproduction:
1. LYTIC CYCLE
-a virus enters a cell and makes copies of itself that
results in the immediate destruction of the host
cell as it LYSES or BURSTS.
5 Steps of Lytic Cycle
• 1. Attachment to the cell
• 2. Penetration (injection) of viral DNA or
RNA
• 3. Replication (Biosynthesis) of new viral
proteins and nucleic acids
• 4. Assembly (Maturation) of the new viruses
• 5. Release of the new viruses into the
environment (cell lyses)
Lytic Cycle Review
• Attachment
• Penetration
• Biosynthesis
• Maturation
• Release
Phage attaches by tail fibers to
host cell
Phage lysozyme opens cell wall,
tail sheath contracts to
force tail core and DNA into
cell
Production of phage DNA
and proteins
Assembly of phage particles
Phage lysozyme breaks cell wall
Bacterial
cell wall
Bacterial
chromosome
Capsid
DNA
Capsid
Sheath
1 Attachment:
Phage
attaches to
host cell.
Tail fiber
Base plate
Pin
Cell wall
Tail
Plasma membrane
2 Penetration:
Phage pnetrates
host cell and
injects its DNA.
Sheath contracted
Tail core
3 Merozoites
released into
bloodsteam from
liver may infect
new red blood cells
Tail
DNA
4 Maturation:
Viral components
are assembled into
virions.
Capsid
5 Release:
Host cell lyses
and new virions
are released.
Tail fibers
2. Lysogenic Cycle
•Phage DNA injected
into host cell
•Viral DNA joins host
DNA forming a
prophage
•When an activation
signal occurs, the
phage DNA starts
replicating
Lysogenic Cycle
•Viral DNA (part of
prophage) may stay
inactive in host cell for
long periods of time
•Replicated during each
binary fission
•Over time, many cells
form containing the
prophages
The Lysogenic Cycle
Viral Latency
•Once a prophage cell is activated, host cell
enters the lytic cell
•New viruses form a & the cell lyses
(bursts)
•Virus said to be virulent (deadly)
ACTIVE
STAGE
INACTIVE STAGE
Viral Latency
•Some viruses have the ability to
become dormant inside the cell
•Called latent viruses
•They may remain inactive for long
periods of time (years)
•Later, they activate to produce new
viruses in response to some external
signal
•HIV and Herpes viruses are
examples
Virulent Viruses
HOST
CELL
LYSES &
DIES
Virulence
VIRUS DESTROYING HOST CELL
Lytic and Lysogenic Cycles
copyright cmassengale
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Viral Disease
Like bacteria, viruses also can cause
disease by disrupting the body’s normal
equilibrium.
Smallpox, measles, mononucleosis,
influenza, colds, warts, AIDS, Ebola
Some viruses may cause some cancers
like leukemia -
Herpes Virus
SIMPLEX I and II
Adenovirus
COMMON COLD
Influenza Virus
Treatment for
Viral Disease
Unlike bacterial diseases,
antibiotics do NOT work on
viruses.
-A vaccine can be used to
prevent a viral disease.
Vaccines
• An attenuated virus is a weakened, less
vigorous virus
• “Attenuate" refers to procedures that weaken
an agent of disease (heating)
• A vaccine against a viral disease can be
made from an attenuated, less virulent strain
of the virus
• Attenuated virus is capable of stimulating an
immune response and creating immunity, but
not causing illness
Other Viral Treatments
•Interferon are naturally
occurring proteins made
by cells to fight viruses
•Genetic altering of
viruses (attenuated
viruses)
•Antiviral drugs (AZT)
•Protease inhibitors –
prevent capsid
formation