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Viruses and Prokaryotes
Chapter 20 pages 572 - 599
Estimated number of viruses on the planet is 1031! If you stacked them up
you would make a tower that would stretch beyond our galaxy and its
neighbors. Every time you get sick with the flu the number of viruses in
your body rises to 100 trillion in a few days. The slide shows viral
abundance in the oceans
Virus – a non-living particle made primarily of proteins and
nucleic acids. They can reproduce only by infecting cells.
Bacteriophage –attacks bacteria
Influenza virus
Lytic infection – viral DNA enters cell, makes copies of itself and causes
the cell to burst (lyse)
Lysogenic infection – viral DNA becomes part of host DNA (prophage) and
may not become active for many generations
Shingles is a viral disease caused by the virus that causes chicken
pox. After recovery from chicken pox the virus lies dormant in the
cells, sometimes for years, before causing its next disease, Shingles.
Chicken pox – highly contagious viral disease. Causes raw pockmarks
that heal. The disease is uncommon now with the advent of the
vaccine.
Common cold is a viral disease of the upper respiratory tract. It is a
retrovirus in that it contains RNA, not DNA. The host cells ribosomes
translate the viral RNA into capsid and other viral proteins. Within 8 hours
the host cell releases hundreds of new viruses to attack other cells.
HIV is a retrovirus that causes AIDS. When this virus infects a cell it makes
a DNA copy of its RNA which is inserted into the host cell DNA. Like a
prophage it may not activate for a while. When it does it programs the cell
to produce viral proteins and RNA.
Helper T cells, when activated by dendritic cells stimulate B cells to
produce antibodies that bind to a specific foreign protein.
The HIV virus attacks T4 helper cells. These are white blood cells that help
acitivate other immune cells when the body is attacked by disease.
• HIV infection sequence
Prokaryotes are either Archaea or Eubacteria. Eubacteria are the
larger of the two domains.
Comparison of Eukarya, Eubacteria and Archaea
Eubacteria cell structure. Gram negative bacteria do not stain
well and are more resistant to antibiotics.
Gram negative bacteria
Gram positive with negative
Archaebacteria cell structure is more similar to Eukaryotes than to
Eubacteria. Archaebacteria lack peptidoglycan in their cell wall.
Bacteria are classified according to cell shape.
Bacterial colony shapes.
Various bacteria colony shapes and colors
Hallophile bacteria colonies. Pink color is the dominant trait.
Needs extremely salty environment to live.
How organisms get energy
Heterotroph – Take in organic molecules from the environment or other
organisms to use as both energy and carbon supply.
This is a low-temperature electron micrograph of a cluster of E. coli
bacteria, magnified 10,000 times. Each individual bacterium is oblong
shaped
Photoheterotrophs – use light for energy, but cannot use CO2 as a source
for carbon. Microscopic view of the bacterium Rhodobacter sphaeroides, a
formaldehyde-ingesting organism which can be used to clean up
contaminated groundwater
Photoautotrophs – Use light energy to convert CO2 into carbon
compounds. This is a picture of Anabena, a common filamentous
cyanobacterium that also fixes nitrogen.
Chemoautotrophs – use energy released by chemical reactions involving
ammonia, hydrogen sulfide, sulfur, ferrous iron and hydrogen. Bacteria
living near this undersea black smoker can breakdown some of the
chemicals to get energy.
Binary Fission – A form of asexual reproduction. Under favorable
conditions bacteria can reproduce every 20 min.
Endospore formation – in poor conditions many bacteria can form an
endospore. These spores have a tough outer coat that resists stains. The
spores can exist for years and “come alive” when conditions are favorable
for growth.
Bacterial conjugation – a hollow bridge forms between two cells
and and exchange of genetic material, a plasmid, occurs. This results
in a cell with a different genetic genotype.
Obligate aerobe bacteria. These bacteria need oxygen to survive.
An example would be Mycobacterium tuberculosis: the bacterium
that causes tuberculosis in human beings.
Tuberculosis bacteria attack the lungs. It is spread through coughing
and sneezing. Most infections do not have symptoms. One in ten
progress to active disease which kills 50% of those untreated.
Tuberculosis can cause extensive scarring in the lungs
Known from antiquity, there was some success in treating
tuberculosis by placing people in sanatoriums, where they could get
fresh air and good food.
Tuberculosis has been treated with a combination of drugs for over
50 years. A challenge is getting people to complete their treatment
after they start feeling better.
Henry David Thoreau died of tuberculosis or consumption as it is
sometimes called.
Nelson Mandela
Ringo Starr
Obligate anaerobe. These bacteria die in the presence of oxygen. they live
deep in the soil, animal intestines or airtight containers. An example is
Clostridium botulinum; the bacterium that causes botulism
A nerve toxin that the bacterium emits is what causes botulism. One
of the initial symptoms is droopy eyelids.
Injections of botulinum toxin type A can remove wrinkles for
up to 4 months.
Facultative anaerobe – this type of bacteria can survive without oxygen
when necessary. Esherichia Coli lives anerobically in sewage and
anaerobically in human intestines.
Bacteria are essential in the decomposition of of organic matter. In this way
they return needed raw materials back into the environment. They are
especially useful in the decomposition of sewage.
A compost pile is a way that people use bacteria to decompose
organic material
Producers – photosynthetic bacteria are important producers. The
cyanobacterium Prochlorococcus is probably the most abundant
photosynthetic organism on the planet.
Prochlorococcus distribution.
Anabena – fresh water cyanobacteria – the heterocysts are cells that
specialize in nitrogen fixation. Akinetes are spore-like cells that
function in reproduction
Nitrogen fixation. Nitrogen is needed to make proteins and other
molecules. Only a few prokaryotes can convert N2 into useful forms. The
process involves turning N2 into ammonia and the ammonia into nitrates
that plants can use or attached to amino acids that all organisms can use
Disease causing bacteria (pathogens) cause disease by destroying
living cells or by releasing chemicals that upset homeostasis. The
slide below shows a person with strep throat.
Releasing Toxins – Some bacteria cause disease because of a
particular deadly toxin they release. Diptheria is an upper
respiratory illness caused by a bacterium that releases a toxin
Meningococcal disease – the bacteria attack the lining of the brain
and the endotoxin they produce can affect the heart and rupture
blood vessels.
A person with meningococcal disease. Even with prompt antibiotic
treatment 10% of infected people die. It is not unusual for patients to
lose hands and feet to this disease.
The endotoxins rupturing of blood vessels can result in amputation.
Even when antibiotics are used early about 10% of the cases will be
fatal.
Controlling bacteria – Washing hands and surfaces with soap.
Soap does not kill the bacteria but it is washed away.
Disinfectants – Chemical solutions (bleach, ammonia, hydrogen peroxide)
can be used to to clean surfaces. Hydrogen peroxide destroys bacterial cell
membranes.
Food storage – refrigeration, canning, pickling, salting, dehydration
can make it difficult for bacteria to grow
Sterilization by heat. Objects can be sterilized when placed boiling
water
Vaccines – A vaccine is a heat killed pathogen or part of a pathogen. The
body responds to the presence of the foreign protein by making antibodies
against the heat killed pathogen. If a live pathogen shows up the antibodies
are already there and the pathogen is defeated before it has a chance to
start.
Polio Vaccine – Developed by Dr. Jonas Salk in 1952. This vaccine
effectively ended the incidence of polio in the US.
A small percentage of people who contracted polio would become
paralyzed as the virus attacked the motor nerves. These patients are
in iron lungs as their chest muscles have become paralyzed.
Franklin D. Roosevelt contracted polio as a young man. He was loathe
to let the public see him in a wheel chair. This one of the few photos
that exist of him sitting in a wheel chair
Jack Nicklaus had polio as a young boy. Fortunately it did not cause any
paralysis. Only .5% of people infected would develop a paralytic symptoms.
But among millions infected this ended up to be a lot of people.
Sister Kenny – a self taught Australian nurse developed a physical therapy
for polio victims that greatly reduced their chances of becoming paralyzed.
She founded and ran the Sister Kenny institute for many years.
Viral diseases do not respond to antibiotics, but some can be
prevented with vaccines. There are some new medications out that
attack specific viral enzymes that host cells do not have.
Campaign to eradicate Polio. Global effort begun in 1988 by WHO – World
Health Organization. Cases have been reduced by 99.9% (From hundreds
of thousands to 291 in 2012). This child is getting the oral vaccine which
contains a weakened virus.
The annual flu vaccine is filled with antigens for three or four influenza
strains. Most of the time this vaccine causes the body to produce the right
antibodies to prevent these viruses from infecting the body.
There are several diseases that have appeared in the past 35 years.
Because there is little history of infection for people our bodies are not well
prepared to produce the antibodies to defeat these pathogens
SARS (Severe Acute Respiratory Syndrome) was found to be a virus
that had jumped from civets to humans. When a disease is able to
infect a new species that species often has trouble defending itself
Antibiotic resistance tests; the bacteria in the culture on the left are
sensitive to the antibiotics contained in the white paper discs. The
bacteria on the right are resistant to most of the antibiotics.
The misuse and overuse of antibiotics allows those bacterial organisms lots
of generations to develop immune strains. The accepted practice of giving
antibiotics to all livestock is one example.
Over time antibiotics are less effective. There are fewer new ones
being developed because the research is not funded well.
Bird Flu – a viral disease that initially infected chickens and evolved to
infect humans. First case in 2003 in china. It is transmitted from infected
birds to people and does not seem to go from person to person yet
Spanish Flu outbreak of 1918. The first of two H1N1 influenza pandemics –
the second in 2009. 500 million people affected and 50 to 100 million died.
US troops fighting in WWI contracted the disease and died at home. The
disease killed up to 20% of the people infected and about 5% of the worlds
population died.
A prion is an infectious agent that is a misfolded protein. When this
protein touches a normal cell protein the normal cell protein is
transformed into the disease causing misfolded protein.
Stanley Prusiner coined the term prion (protein infectious agent), to
describe the proteins he found in sheep afflicted with scrapie (1972). He
was strongly criticized for his work, but ended up with the Nobel prize in
medicine in 1997.
Scrappie is a fatal, degenerative disease that affects the nervous
system of sheep and goats. It is related to BSE (bovine spongiform
encephalopathy) or “mad cow disease” and chronic wasting disease.
This slide shows samples of brain tissue and compare scrapie with
KURU and CJD – other spongiform brain diseases
Mad Cow disease is BSE in humans. Cattle were getting the disease
through protein additives in their feed and humans would get the
disease by eating hamburger that included protein from the brain
and spinal cord. This disease first struck Great Britain in 1988.
Chronic Wasting disease. This is BSE in deer, moose and elk. Both
Minnesota and Wisconsin have periodically required hunters to have
their deer checked for CWD. In 2012 Minnesota required this from an
area where captive deer where found with CWD
To date, no strong evidence exists that CWD can be passed on to humans.
Many people strongly encourage others to not include nervous tissue in the
preparation of hamburger or sausage as that is where the prions are
located. This map shows CWD, by county, in 2013