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Bacteria
And
Viruses
Inside this
Issue:
Volume 1, Issue 2
Newsletter 2011
By Professor Dante Joa, CHI
What bacteria do?
2
How does it help
cows?
2
Antibiotics
2
Viral Morphology
2
Fixing Nitrogen
in soil
2
VIRUSES
3
Are viruses even
alive?!?!
3
TYPES OF VIRUSES
3
Smaller than viruses
4
Influenza Serology 4
and Epidemiology
Complications of
influenza
5
Treatment and
Control
5
ORTHOMYXO VIRUS
5
Bacteria Basics.- They are alive!
Bacteria are the simplest of
creatures that are considered
alive. Bacteria are everywhere. They are in the bread
you eat, the soil that plants
grow in, and even inside of
you. They are very simple
cells that fall under the heading prokaryotic. That word
means they do not have an
organized nucleus. Bacteria
are small single cells whose
whole purpose in life is to
replicate.
Okay. So we've told you they
don't have an organized nu-
cleus. True. They do have
DNA. It is grouped in an area
called the nucleoid. They
have cell membranes like
other cells and even a protective cell wall. Mind you, their
cell wall is not like the one in
a plant. It's a special kind
that bacteria have for protection. They don't have any organelles, just ribosomes.
(These are all characteristics
of prokaryotes if you remember.)
What do they look like?
Very, very small.
You might have
seen pictures of
some bacteria.
Since we don't
know what you
have seen, we'll
tell you there are
three basic shapes.
Spherical bacteria
are in the shape of
little spheres or
balls. They usually
form chains of
cells like a row of
circles. Rod
shaped bacteria
are look like the E.
coli living in your
intestine. You can
imagine a bunch
of bacteria that
look like hot dogs.
They can make
chains like a set of
linked sausages.
Spiral shaped bacteria twist a little.
Think about balloon animals for
these shapes. It's
like a balloon animal in the shape
of a corkscrew.
Bacteria
Human Bacteria
Fixing Nitrogen
in soil
There are bacteria that go
through a process called
fixing nitrogen. These bacteria, living in the roots of
plants, actually help them
absorb nitrogen from the
surrounding soil. The nitrogen is very important
for the growth of the plant,
and these little bacteria
give them an advantage for
survival.
Nitrogen
-fixing
bacteria
protect
soybeans
Page 2
What do bacteria do?
All sorts of things. Sorry
to be so vague, but they
do just about everything.
Some help plants absorb
nitrogen (N) from the
soil. Some cause diseases
like botulism. Some bacteria even live inside the
stomachs of cows to help
them break down cellulose. Cows on their own
can digest grass and
plants about as well as
we do. They don't get
many nutrients out of the
plants and can't break
down the cellulose. With
those super bacteria, the
cellulose can be broken
down into sugars and
then release all of the energy they need. Imagine if
scientists could develop
bacteria to live inside of
us that would break
down plants. That would
be something. We could
eat grass and leaves all
day long.
Helping cows eat grass
As we said, not all protists
are bad for the world. In
the bacteria section we already told you about a species that lives in the digestive system in cows. These
bacteria help cows break
down the cellulose in
plants. Similar bacteria live
in all sorts of grazing animals, helping them survive
off plant material. Many
ecosystems are based on
ANTIBIOTICS
Scientists have even discovered fungi that will help you
battle bacterial diseases. So you get sick, the doctor
looks at you and says you have a bacterial infection,
maybe bronchitis. He prescribes an antibiotic to help
you get better. Antibiotics are drugs designed to destroy
bacteria by weakening their cell walls. When the bacterial cell walls are weak, your immune cells can go in and
destroy the bacteria. Although there are many types
now, one of the first antibiotics was called penicillin. It
was developed from a fungus (a fungus named Penicillium found on an orange, to be exact).
Viral Morphology
They say we learn best by
doing, so let’s study viral
structure by making a virus,
starting from the nucleic
acid inside and proceeding
to the capsid and envelope.
Virus are classified as either
DNA or RNA viruses. So we
have two choices for our virus: DNA or RNA . of course
nothing is quite that simple.
The nucleic strands can be
single-stranded, double
stranded, linear, or looped,
in separated segments or
one continuous strand. The
nucleic acid sequences can
encode a simple message or
encode hundreds of enzymes and structural proteins.
Volume 1, Issue 2
Page 3
VIRUSES
Viruses
Have these
unique
characteristics:
1. They are energy –less. They float around until they come in contact with an appropriate cell.
2. They are basic life forms composed of a protein coat, called a
capsid, that surrounds genetic material.
3. Viruses do not have organelles or ribosomes. Certain viruses are
futher enclosed by an external lipid bilayer membrane that surrounds the capsid and may contain glycoproteins. Some viruses
also carry some structural proteins and enzymes inside their
capsid.
4. The genetic material is either Dna or RNA. Never both!! The genetic material contains instructions to make millions of clones
of the original virus.
5. Replication of the genetic material occurs when the virus takes
control of the host cell’s synthetic machinery. Viruses contain
all of the genetic information, but no the enzymes, needed to
build millions of replicas of the original virus
TYPES OF VIRUSES
As you go on to study more
biology, you'll see many virus
types. There are three basic
shapes.
1) First there are helical virions. They are set up like a
tube. The protein coat winds
up like a garden hose around
the core.
2) Next comes the polyhedral
shape. This shape group includes the classic virus shape
that looks like a dodecahedron. A dodecahedron is a
geometric shape with twelve
(12) sides. These viruses have
many facets and a seemingly
hard shell of capsomeres
(pieces of a capsid). There is
a variation of the polyhedral
called globular. Globular
shapes are basically polyhedral virions inside of a
spherical (like a ball) envelope.
3) Last is the complex virus
shape. You may have seen
this one in books with the
geometric head and long
legs.
Are viruses even alive?!?!
We're starting with the smallest
of the small here. Some scientists argue that viruses are not
even living things. We suppose
it's easier to give you a list of
what they can't do as opposed
to what they can. What viruses
can't do:
(1) They can't reproduce on
their own. They need to infect
or invade a host cell. That host
cell will do all the work to duplicate the virus.
(2) They don't respond to anything. You can poke them or set
up barriers, it doesn't matter.
They either function or they are
destroyed.
(3) They don't really have any
working parts. While there
some advanced viruses that
seem fancy, viruses don't have
any of the parts you would normally think of when you think
of a cell. They have no nuclei,
mitochondria, or ribosomes.
Some viruses do not even have
cytoplasm.
We've already established what
viruses aren't. Let's talk about
what they are. Every virus has a
few basic parts. The most important part is a small piece of
DNA or RNA (never both). That
strand of nucleic acid is considered the core of the virus. The
second big part is a protein coat
to protect the nucleic acid. That
coat is called the capsid. The
capsid protects the core but
also helps the virus infect new
cells. Some viruses have another coat or shell called the
envelope. The envelope is made
of lipids and proteins in the
way a regular cell membrane is
structured. The envelope can
help a virus get into systems
unnoticed and help them invade new host cells.
Smaller than viruses
o
Pri
ns
There are things out there even
smaller than viruses. The two that
scientists have discovered are
called prions and viroids. A prion is
(as far as we know) just a protein.
Prions are proteins that can invade
cells and somehow direct their own
duplication, making more of the
isolated proteins. Viroids are a little
different in that they are just RNA.
Scientists have even discovered
that they are responsible for some
diseases.
Influ
en
Viroi za
ds
Influenza Serology and Epidemiology
Major mutational changes
usually result in altered
codon reading frames and a
nonviable virus.
Q: We all think that this is a
pesky but mild self-limiting
disease. It can cause pneumonia and more serious disease
in the elderly, but usually it
resolves without complications in 3 to 7 days. So why
When looking at the disease
have there been devastating
influenza, 2 questions about pandemics of influenza
epidemiology arise:
throughout history, as in
1918? Over a few weeks in
Q: If an antibody to the NA
1918,548,452 persons in the
and HA are protective, why
U.S., 12.5 million persons in
do we continually get epiIndia, and 20 million persons
demics of the bothersome
worldwide died from this viflu, with fever chills, myalrus.
gias, arthralgias, headache,
A: Antigenic Shift: Now we
are really shifting gears. We
and other miseries.
are taking the boat menA: Antigenic Drift: During vi- tioned above and airlifting it
ral replication mutations can to a mountain in the Himalaoccur in the HA or NA, lead- yas. With antigenic shift
ing to changes in the antithere is a complete change of
genic nature of these glycothe HA, NA or both. This can
proteins. This is termed anti- only occur with influenza
genic drift because the
type A because the mechachanges are small, just a lit- nism involves the trading of
tle drift of the sailboat in the RNA segments between aniwater. The resulting new
mal and human strains.
strains are only partially atWhen 2 influenza types cotacked by our immune sysinfect the same cell, undergo
tem, resulting in milder dis- replication and capsid packease in adults who have pre- aging, RNA segments can be
viously acquired antibodies. mispackaged into another viThere are 3 types of influenza virus: A, B, and C. These
types have many strains
separated by antigenic differences in HA and NA. Type A
infects humans, other mammals (swine, etc.), and birds.
Type B and C have only been
isolated from humans.
Swine Flu
Virus
rus. This virus now wields a
new HA or NA glycoprotein
that has never been exposed
to a human immune system
anywhere on the planet. So
the entire human population
would be susceptible, leading
to devastating pandemics.
The new HA and NA antigens
are given number subscripts
to differentiate them. The
pandemic of 1889 was
caused by a virus with an H2
hemagglutinin, the pandemic
of 1900 was caused by a new
virus with H3 hemagglutinin;
in 1918 a swine flu virus
transferred its HA to a human virus and so was called
Hswine hemagglutinin (HSW).
The chart below is only included to demonstrate the
many pandemics and their
new HA and NA antigenic
composition.
1989 H2N2
1900 H3N2
1918 HswN1
1947 H1N1
1957 H2N2*
1968 H3N2*
1977 H1N1*
*Notice also that some
strains can cause a second
pandemic as a new unexposed population grows to
adulthood.
Complications of influenza
Even the normal yearly flu can cause complications. The elderly and immunocompromised suffer more serious illness
as the virus spreads to the lower respiratory tract, resulting
in pneumonia. The viral infection also lowers the host defenses against many bacteria. Secondary bacterial pneumonias by Staphylococcus aureus, Streptococcus pneumoniae,
and others are common and the physician must follow patients (especially the elderly) closely until complete resolution of their illness. New fevers or failure to improve means
danger!!
Treatment and Control
Influenza viruses are grown in mass
quantities in chick embryos, which are
then inactivated, purified, and used as
vaccines. Scientists carefully choose 3
strains that are circulating in the population or expected to cause an outbreak
in the next season. These vaccines have
variable success depending on the accuracy of the “guesswork”. The vaccines
should be given to the elderly, immunocompromised patients, and health care
workers.
A drug called amantadine prevents the
uncoating of influenza A. This medication can prevent infection if given daily
before exposure, or it can decrease the
severity of the illness if given early in
the course.
ORTHOMYXO VIRUS
Morphology
1. Negative (-) singlestranded RNA
2. Segmented (7-8)
3. Lipid containing envelope
4. Helical symmetry
5. Replicates in the nucleus!
(Retroviruses are the only
other
type of RNA viruses that
replicate
in the nucleus)
Virulence Factors
1. Hemagglutinin (HA) glycoprotein:
binds tored blood cells. Also
binds
to receptors on cells of the
upper
respiratory tract, resulting
in dumping
of viral RNA into these cells.
2. Neuraminidase (NA) glycoprotein:
breaks down neuraminic
acid, an
important component of
mucin
Clinical
The Flu: Fever, runny nose,
cough, myalgias, arthralgias,
etc.
*Complications
1. Secondary bacterial pneumoniasin the elderly
2. Reyes Syndrome in children
who use aspirin; get liver
and brain
disease.
Treatment & Prevention
1. Vaccine
2. Amantadine:
Prevents uncoating of influenza type A.
Miscellaneous
1. Antigenic drift: small mutations
resulting in minor changes
in the
antigenicity of HA or NA .
This
results in epidemics of the
common
flu
2. Antigenic shift (only occurs with
influenza type A): reassortment
Major changes of the HA or
NA
(including acquisition of animal HA
or NA). This results in devastating
influenza pandemics
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