Download Viruses and Prokaryotes Chapter 18

Viruses and Prokaryotes
18.1- Studying Viruses and
Prokaryotes
• A virus is an infectious
particle made only of a strand
of DNA or RNA surrounded
by a protein coat
• A bacteria is a one-celled
organism that can also cause
infections
18.1- Studying Viruses and
Prokaryotes
• Viruses and bacteria
are pathogens.
Pathogens are
organisms or particles
that cause diseases.
However, this is where
the similarities end.
18.1- Studying Viruses and
Prokaryotes
• A virus is a problem for
scientists because they don’t
even believe it is a living
organism.
• Living things have certain
characteristics:
• They must show most notably
reproducing on their own
(VIRUSES CANNOT DO THIS)
• In fact, viruses are not anywhere in
Linnaean classification.
18.1- Studying Viruses and
Prokaryotes
• Other structures called
viroids are even less like
living things. Viroids cause
diseases in plants.
• Finally, prions are the least
likely to be living. These are
just proteins that cause other
proteins to act incorrectly.
18.1- Studying Viruses and
Prokaryotes
• Viruses, Viroids, and Prions are all particles that
cause infections but are not considered living
things because they do not have all the
characteristics of living organisms
18.2- Viral Structure and Reproduction
• Virus’ structure is very basic. It
is made up of genetic material
(DNA or RNA) surrounded by
a protein shell called a capsid.
• Viruses have many different
shapes and sizes. Their shape
usually tells us something
about how it infects a host cell
18.2- Viral Structure and Reproduction
• A virus can only reproduce with the help of a host
cell.
• It has no mechanism to do it by itself: it has no
organelles, membranes, no need for oxygen or
ATP.
• It simply carries its genes to a cell and has that cell
copy the genes for the virus
18.2- Viral Structure and Reproduction
• Viruses are specific.
• Certain viruses can only infect
certain cells because of the viral
shape.
• For example, the bacteriophage is
a virus that ONLY infects
bacteria.
• The bacteriophage has a
specific shape that
allows it to anchor to
bacteria and inject its
DNA. The whole
bacteriophage does not
enter the bacteria
18.2- Viral Structure and Reproduction
• Viruses that infect eukaryotes differ from bacteriophages
in the way they enter cells.
• Generally, the whole virus enters the cell through
endocytosis.
• Regardless of how viruses get into their host cells, all cause
infection.
• Only two types of infection a virus causes
• LYTIC INFECTION
• LYSOGENIC INFECTION
18.2- Viral Structure and Reproduction
• A lytic infection causes the host
cell to burst releasing new viral
offspring into the host’s system
and each new virus infects
another cell.
• This type of infection happens
very quickly.
18.2- Viral Structure and Reproduction
• A lysogenic infection merges
together the host cell’s DNA and
the viral DNA.
• The viral DNA combines with the
host cell DNA to create a prophage.
• As the cell gets ready for mitosis,
it copies it’s DNA and
unknowingly copies the viral
DNA as well.
• This viral DNA then gets passed on to
two more cells. This can go on forever
or at anytime the prophage can
activate and burst all infected cells.
18.2- Viral Structure and Reproduction
18.4- Bacteria and Archaea
• Prokaryotes, which include
bacteria and archaea are the most
widespread organisms on earth.
There are approximately (10^30)
prokaryotes on Earth.
• These organisms live on about
every square inch of Earth
including rocks, soil, polar ice
caps, deserts, and volcanoes.
• Scientists also acknowledge there
may be as many as 1 billion
different types of bacteria
18.4- Bacteria and Archaea
• Prokaryotes are grouped based upon their need
for oxygen:
• Obligate Anaerobes- can not live in the presence of
oxygen and are actually poisoned by it. These organisms
live in the harshest enviornments on Earth
• Obligate Aerobes- Organisms that must have oxygen to
survive
• Facultative Aerobes- these types of organisms can live
with or without oxygen
18.4- Bacteria and Archaea
18.4- Bacteria and Archaea
• Domain Bacteria and Domain Archaea
comprise all prokaryotes on Earth.
• Domain Bacteria are more diverse and are the ones you
encounter of a daily basis.
• Domain Archaea are the prokaryotes that live in the
harshest of environments.
• However, these two groups have some
similarities.
18.4- Bacteria and Archaea
Structural Comparisons• Under the microscope, Archaea and
Bacteria look very similar.
• Both are single-celled,
prokaryotic, and have cell
walls
• Most all of Bacteria and
Archaea come in
generally 3 different
shapes
1. Rod-Shaped
(Bacilli)
2. Circle-Shaped
(Coccus)
3. Spiral-Shaped
(Spirilla)
18.4- Bacteria and Archaea
• Most all prokaryotes have no membranebound organelles.
• Their DNA is free-floating in the cytoplasm.
• They also have a structure called a plasmid, that is a
small piece of genetic material that can replicate
separately from regular chromosome.
18.4- Bacteria and Archaea
• Most all prokaryotes
move on their own• Most use a flagella, which
is a whip-like tail at the end
of the organism. While
looking the same, the
flagella of Bacteria and
Archaea are differently
structurally.
• Some also have pili, which
are shorter extensions all
around the cell.
18.4- Bacteria and Archaea
Molecular Comparisons• Molecular analysis techniques finally
allowed scientists to see the many
differences between Bacteria and Archaea.
• Actually, most scientists believe archaea are
more closely related to Eukaryotes rather
than Bacteria.
• Archaea contain lipids in their cell
membranes and walls
18.4- Bacteria and Archaea
Molecular Comparisons (cont.)
• Bacteria, however, contain a substance
called peptidoglycan, a polymer only
found in Bacteria.
• The amount of peptidoglycan in the
cell walls is an important
characteristic of Bacteria.
• This polymer is detected by a process
called Gram-Staining.
18.4- Bacteria and Archaea
Gram-Staining• Bacteria are placed in 2 groups
based on this test: Gram tests
are used to detect the amount of
peptidoglycon in a cell wall.
• Gram-Negative: Stains
red and means there is
only a thin layer of
peptidoglycan
• Gram-Positive: Stains
purple and means there
is a very thick layer of
peptidoglycan
18.4- Bacteria and Archaea
18.4- Bacteria and Archaea
• Prokaryotes have found numerous
ways to survive and pass on genes:
They are very quick at adapting to
a new environment.
• Most prokaryotes reproduce asexually
and binary fission the chromosome
copies itself and the cell doubles in size
and then splits in half.
• Prokaryotes can sexually reproduce
through conjugation the pili of each
prokaryote connect and this connection
is used to exchange genes
18.4- Bacteria and Archaea
• Prokaryotes can also survive unfavorable
conditions by certain an endospore.
• This is a specialized cell with a thick wall to protect
the prokaryotes from harsh conditions
18.5- Beneficial Roles of Prokaryotes
• Prokaryotes, such as
bacteria, are a key part of
animal digestion of foods.
• If we didn’t have these bacteria,
it would take up to 7 days to
digest food.
• They (bacteria) also make
vitamins and other
compounds and keep other
microbes away.
• The bacteria gets a place to live
and food.
18.5- Beneficial Roles of Prokaryotes
• Prokaryotes benefit us
in other ways too.
• Many of the foods we
enjoy are fermented by
bacteria.
• Yogurt, cheese, pickles,
soy, sauerkraut, and
vinegar depending of
prokaryotes to be made.
18.5- Beneficial Roles of Prokaryotes
• Prokaryotes also help balance the ecosystem:
• Some, like cyanobacteria, produce oxygen while others
recycle carbon and other gases
• Other bacteria fix nitrogen so plants can use it: Plants
need nitrogen, but can’t use it in it’s atmosphere gas
form.
• Bacteria takes atmospheric nitrogen and converts it to
ammonia for plants to use.
• Soybeans would not survive without this benefit
18.5- Beneficial Roles and Prokaryotes
• Some prokaryotes can even be used to clean
the environment.
• So bacteria digests oil, helping in oil spills.
• Bacteria also breaks down decaying organic
matter.
18.6- Bacterial Diseases and
Antibiotics
• Bacteria can cause sickness for a host
organism in two ways:
1.Invading Tissues
2.Releasing Toxins
• EXAMPLES:
1. Tuberculosis- invading lung tissues
and kill white bloods cells
2. Botulism (Food Poisoning)- caused by
toxins released by a bacteria called
clostyidium botulinum.
18.6- Bacterial Diseases and
Antibiotics
Antibiotics• These are medications that
fight bacterial infection.
• THEY DO NOT FIGHT
VIRAL INFECTIONS
LIKE COLDS AND
FLUS!!!
18.6- Beneficial Diseases and
Antibiotics
• Antibiotics work by not allowing bacteria to
create cell walls so they cannot reproduce.
• Some organisms, such as some fungus, create
antibiotics normally.
• Antibiotics, however, should not be the 1st line
of defense against infections, prevention
should be…………WASH YOUR HANDS!!
18.6- Bacterial Diseases and
Antibiotics
• Finally, when given an antibiotic, do not abuse
it, but instead, follow the directions.
• When mis-used, bacteria can build-up a
resistance to antibiotics.
• Mis-using involves using too much or not taking all of
antibiotics of a given course of treatment.
• Both of these cases create “superbugs” that are
bacteria that can resist almost any antibiotic.