Download Ch. 19 Bacteria and Viruses

Ch. 19 Bacteria and Viruses
Ch. 19 Outline
• 19-1: Bacteria
– Classifying prokaryotes
– Identifying Prokaryotes
– Metabolic Diversity
– Growth and Reproduction
– Importance of Bacteria
Bacteria
• Once microscopes were invented, scientists
discovered a world of microorganisms.
• The smallest and most common microorganisms
are the prokaryotes, which are single-celled
organisms that lack a nucleus
• The word bacteria is so familiar, that we will use it
as a common term to describe prokaryotes
Ch. 19 Outline
• 19-2: Viruses
–
–
–
–
What is a virus?
Viral Infection
Retroviruses
Viruses and Living Cells
• 19-3 Diseases caused by bacteria and
viruses
–
–
–
–
Bacterial Diseases in Humans
Controlling Bacteria
Viral Diseases
Viroids and Prions
Bacteria
• Prokaryotes range in size from 1 to 5 micrometers
in diameter. There are exceptions to this rule. The
Epulopiscium fisheloni is about 500 micrometers
long.
Classifying Prokaryotes
• All prokaryotes were once classified in a
single Kingdom named Monera.
• Two Kingdoms of bacteria: Eubacteria,
Archaebacteria
• Some scientists think that the Eubacteria
and Archaebacteria should be classified as
Domains.
Classifying Prokaryotes
• Eubacteria: the larger of the two kingdoms
• Some live in fresh water, salt water, land, on and
within the human body. They can infect large
animals
– Eubacteria cell walls protects the cell from injury and
determines its shape
– Eubacteria cell walls contain peptidoglycan, a
carbohydrate
– Inside the cell wall, a cell membrane protects the
cytoplasm of eubacteria. Some eubacteria have a
second cell membrane outside the cell membrane
Classifying Prokaryotes
• Archaebacteria are similar to Eubacteria in that
they are equally small, lack nuclei, and have cell
walls
• Archaebacteria do not have peptidoglycan in their
cell walls, plus they have different membrane lipids
• Also, the DNA sequences of key archaebacteria are
more like those of eukaryotes than those of
eubacteria
• ****archaebacteria may possibly be
ancestors of eukaryotes****
tainano.com
Classifying Prokaryotes
• Many archaebacteria live in harsh environments.
One group of arcaheabacteria is the methanogens,
that produce methane gas.
• Methanogens Use only CO2, H and N to produce
energy to live, and as a result give off methane gas.
• Live in swamps, marshes, gut of cattle, termites, etc.
• Methanogens are decomposers
• Other archaebacteria live in
extremely salty environments or in
hot springs, mud or digestive tracts
of animals
www.biology.iupui.edu/.../N100/2k23domain.html
Classifying Prokaryotes
Bacteria
are classified into the kingdoms of
include a variety of
lifestyles such as
live in harsh
environments such as
Classifying Prokaryotes
Bacteria
are classified into the kingdoms of
Eubacteria
Archaebacteria
include a variety of
lifestyles such as
Living in
soil
Infecting
large
organisms
live in harsh
environments such as
Thick mud
Animal
digestive
tracts
Salty lakes
Hot springs
Identifying Prokaryotes: Shapes
• Prokaryotes are identified by:
– Their shape
– The chemical nature of cell walls
– The way they move
Identifying Prokaryotes: Shapes
Rod-shaped prokaryotes are called bacilli
Spherical shaped prokaryotes are called
cocci
Spiral and corked-shaped prokaryotes are
called spirilla
Identifying Prokaryotes: Cell Walls
• Two different types of cell walls are found in
Eubacteria
• A method called Gram staining is used to tell
the two different types of cell walls apart
• Violet stain is used to stain the peptidoglycan
cell walls
• Alcohol treatment may wash away the violet
stain. If the violet stain remains, then the
bacteria are said to be Gram-positive
• These bacteria have thick peptidoglycan
cell walls
Identifying Prokaryotes: Cell Walls
• Gram-negative bacteria have much thinner
cell walls inside an outer lipid layer
• Alcohol dissolves the lipid and removes the
violet stain from the cell walls. The
counterstain makes these bacteria appear
pink
Identifying Prokaryotes: Cell Walls
•
What does the type of cell wall have to do with
a bacterium’s resistance to antibiotics?
 Gram negative bacteria’s extra layer outside
the cell wall can make it hard for some
antibiotics to get inside the cell (where they
can work).
 That makes it important for a doctor to know
what kind of bacteria is causing the infection so
that most effective antibiotic can be used to
treat it.
Identifying Prokaryotes: Movement
• How are the ways prokaryotes move?
– Some do not move
– Propelled by flagella
– Lash snake or spiral forward
– Glide
• Which characteristic of prokaryotes
illustrates their diversity best?
By the way they obtain energy
Identifying Prokaryotes: Metabolic Diversity
• Which characteristic of prokaryotes illustrates
their diversity best?
– By the way they obtain energy
• Most prokaryotes are heterotrophs, meaning
they get their energy by consuming organic
molecules made by organisms
• Other prokaryotes are autotrophs and make
their own food from inorganic molecules
Identifying Prokaryotes: Metabolic Diversity
• Most heterotrophic prokaryotes must take in
organic molecules for both energy and a
source of carbon. These are called
chemoheterotrophs.
• Humans are also chemoheterotrophs
• If human food is not handled carefully,
bacteria may eat our food and release
toxins that cause food poisoning
Identifying Prokaryotes: Metabolic Diversity
• Photoautotrophs use light energy to convert carbon
dioxide and water to carbon compounds and oxygen
• Photoautotrophs are found where light is plentiful
• The photoautrophs Cyanobacteria contain a bluish pigment
and chlorophyll. They are found everywhere (land, salt and
fresh water) and are the first to recolonize an area after a
natural disaster.
Identifying Prokaryotes: Metabolic Diversity
• Chemoautotrophs perform chemosynthesis.
• They make organic carbon molecules from
carbon dioxide.
Identifying Prokaryotes: Metabolic Diversity
• Chemoautotrophs do not require light as a source
of energy. Instead, they use energy directly from
chemical reactions involving ammonia, hydrogen
sulfide, nitrites, sulfur or iron
• Some live deep in the darkness of the ocean
• They use hydrogen sulfide gas that flows from
hydrothermal vents in the ocean
Identifying Prokaryotes: Metabolic Diversity
• Like all organisms, bacteria need a constant
supply of energy. This energy is released by
the process of cellular respiration or
photosynthesis or both
• Organisms that require a constant supply of
oxygen to live are called Obligate Aerobes
• Obligate Anerobes DO NOT REQUIRE
oxygen and may be killed by it
Clostridium botulinum
Clostridium botulinum
•
Obligate Anerobe
found in soil
•
Gram positive
•
Rod-shaped
•
Grow in can foods
that have not been
properly sterilized
• Faculative Anerobes can live with or without
oxygen
• Faculative anerobes can live anywhere
because they can switch between the
processes of cellular respiration or
fermentation depending on their environment
Escherichia Coli (E. Coli)
• Faculative
anerobe
• Gram negative
• Rod shaped
• Lives anerobically
in large intestine
• Lives aerobically
in sewage or
contaminated water
Escherichia Coli (E. Coli)
•
Eschericha coli
are normal
inhabitants of our
digestive tract
•
A new strain of E.
coli (O157:H7)
has caused illness
and death for
people who ate
contaminated
hamburger meat.
Escherichia Coli (E. Coli)
Growth and Reproduction
• Bacteria can not grow and divide
indefinitely because of the availability of
food and they have to get rid of wastes
• Bacteria grow and divide very rapidly.
Their method of division is called binary
fission
– Bacteria grow until they double in size, copies
DNA and simply splits into two daughter cells
– Binary fission is just asexual reproduction
(no exchange of genetic material)
Binary Fission
http://www.swt.edu/~rr33/
Growth and Reproduction
• Conjugation: A
process of exchanging
genetic info in bacteria
– A hollow bridge forms
between two bacterial
cells and genes move
from one cell to the
other
– Increases genetic
diversity of bacteria
Growth and Reproduction
• When growth conditions become
unfavorable, many bacteria produce
spores, which can remain dormant until
there are more favorable growth conditions.
– Endospore: one type of spore formed when a
bacterium produces a thick internal wall that
encloses its DNA and a portion of its cytoplasm.
Importance of Bacteria
• We could not survive without bacteria. Some
are producers, others are decomposers,
and some are used by humans for various
things.
Endospores
Importance of Bacteria
• We could not survive without bacteria. Some are
producers, others are decomposers, and some are used
by humans for various things.
• Decomposers
– Bacteria help recycle nutrients in the environment
– Attack and digest dead tissue
– Break down complex compounds in sewage to simpler
ones
– Produce purified water
– Produce nitrogen and carbon dioxide gases
– Produce fertilizer compounds
Importance of Bacteria
• Nitrogen Fixers
– PLANTS NEED NITROGEN TO MAKE AMINO ACIDS
which are used to make PROTEINS
– Plants can not use nitrogen gas (N2) directly. Nitrogen
must first be changed chemically to ammonia (NH3) or
other nitrogen compounds. The process of converting
nitrogen gas to a form that plants can use is called
nitrogen fixation.
– Many plants have symbiotic relationships with nitrogenfixing bacteria. The bacterium Rhizobium, grows on the
roots of soybean plants. The plant provides nutrients for
Rhizobium, and it converts nitrogen gas in the air to
ammonia, which helps the plant.
Importance of Bacteria
• Human Uses of Bacteria
– Produce a wide variety of food and beverages
– Industry  cleaning up oil spills (digest
petroleum)
– Mine minerals from the ground
– Remove wastes and poisons from water
– Synthesize drugs and chemicals (genetic
engineering)
– Produce vitamins in human intestines
– Produce heat stable enzymes that can be used
in medicine, food production, and industrial
chemistry
Ch. 19 Outline
• 19-2: Viruses
–What is a virus?
–Viral Infection
–Retroviruses
–Viruses and Living Cells
What is a Virus?
• The word virus is derived from the Latin word for
poison
• Dmitri Ivanovski identified the cause of tobacco
mosaic disease by extracting juice from an
infected plant
• Martinus Beijerinck suggested that tiny particles
in the extracted juice caused tobacco mosaic
disease (called particles viruses)
• Wendell Stanley inferred that viruses were not
alive when he obtained crystals of tobacco
mosaic virus
What is a Virus?
• The word virus is derived from the Latin word for
poison
• Viruses: particles of nucleic acids, proteins and in
some cases, lipids
• Viruses are NON-LIVING, but they do reproduce.
• Viruses can reproduce only by infecting living cells
and once inside, they use the machinery of the
infected cell to produce more viruses
Viral Structures
A typical virus is composed of a core of DNA
or RNA surrounded by a protein coat.
What is a Virus?
• The simplest virus may have only a few
genes, whereas the most complex may
have more than a hundred genes
• A viruses protein coat is called its capsid.
The capsid includes proteins that enable a
virus to enter a host cell.
• The capsid proteins of a typical virus bind
to receptors on the surface of a cell and
“trick” the cell into allowing it inside.
What is a Virus?
• Once inside, the viral genes are expressed.
The cell transcribes and translates the viral
genetic information into viral capsid proteins
• Sometimes the genetic program causes the
host cell to make copies of the virus, and in
the process the host cell is destroyed.
What is a Virus?
• Viruses must bind precisely to proteins on the cell
surface and then use the host’s genetic system
• Viruses that infect bacteria are called bacteriophages
Viral Infection
• There are two types of viral infections: lytic and lysogenic
• Lytic Infection
– The virus enters the cell, makes copies of itself, and
causes the cell to burst (destroyed)
– In a lytic infection, the protein capsid is activated by
contact with a specific host cell
– It then injects its DNA directly into the host cell.
– The host cell cannot tell the difference between its own
DNA and the DNA of the virus
Viral Infection
– Consequently, the cell begins to make
messenger RNA from the genes of the virus
– This viral mRNA is translated into viral proteins
that act like a molecular wrecking crew,
chopping up the cell DNA, a process that shuts
down the infected host cell
– In this lytic infection, the virus then uses the
materials of the host cell to make thousands
of copies of its own DNA molecule
Viral Infection
– The viral DNA gets assembled into new virus
particles
– Before long, the infected cell lyses or bursts,
and releases hundreds of virus particles that
may go on to infect other cells
– Because the host cell is lysed and
DESTROYED, this process is called a lytic
infection
Viral Infection
• Lysogenic Infection
– A host cell makes copies of the virus
indefinitely
– A virus incorporates its DNA into the DNA of
the host cell, and the viral genetic information
replicates along with the host cell’s DNA
– Lysogenic viruses do not lyse the host cell
right away. A lysogenic virus remains inactive
for a period of time
Viral Infection
– The viral DNA that is embedded in the host’s
DNA is called a prophage
– The prophage may remain part of the DNA of
the host cell for many generations before it
becomes active.
– Eventually, from any number of factors, the DNA
of a prophage will be activated. It will remove
itself from the host cell DNA and direct the
synthesis of new virus particles
Lytic Vs. Lysogenic
Retroviruses
• Retroviruses: viruses that have RNA as their
genetic material.
• When a retroviruses infect a cell, they
produce a DNA copy of their RNA. This DNA,
much like a prophage, is incorporated into
the DNA of the host cell.
• There the retrovirus may remain dormant for
varying lengths of time before becoming
active
Retroviruses
• Retroviruses get their name from the fact that
their genetic information is copied
backwards, that is from RNA to DNA instead
of from DNA to RNA.
• The prefix retro means backwards
• The virus that causes acquired immune
deficiency syndrome (AIDS) is a retrovirus
and some cancers are caused by
retroviruses
Figure 18.9 The structure of HIV, the retrovirus that
causes AIDS
Glycoprotein
Viral envelope
Capsid
Reverse
transcriptase
RNA
(two identical
strands)
Figure 18.10 The reproductive cycle of HIV,
a retrovirus
HIV
Membrane of
white blood cell
1 The virus fuses with the
cell’s plasma membrane.
The capsid proteins are
removed, releasing the
viral proteins and RNA.
2 Reverse transcriptase
catalyzes the synthesis of a
DNA strand complementary
to the viral RNA.
HOST CELL
3 Reverse transcriptase
catalyzes the synthesis of
a second DNA strand
complementary to the first.
Reverse
transcriptase
Viral RNA
RNA-DNA
hybrid
4 The double-stranded
DNA is incorporated
as a provirus into the cell’s
DNA.
0.25 µm
HIV entering a cell
DNA
NUCLEUS
Chromosomal
DNA
Provirus
5 Proviral genes are
transcribed into RNA
molecules, which serve as
genomes for the next viral
generation and as mRNAs for
translation into viral proteins.
RNA genome
for the next
viral generation
mRNA
6 The viral proteins include capsid
proteins and reverse transcriptase
(made in the cytosol) and envelope
glycoproteins (made in the ER).
New HIV leaving a cell
9 New viruses bud
off from the host cell.
8 Capsids are
assembled around
viral genomes and
reverse transcriptase
molecules.
7 Vesicles transport the
glycoproteins from the ER to
the cell’s plasma membrane.
Viruses and Living Cells
• Viruses must infect a living cell in order to
grow and reproduce
• Viruses take advantage of the host’s
respiration, nutrition, and all other functions
and are therefore parasites
• Viruses are not alive because they are not
made up of cells and are able to live
independently
Viruses and Living Cells
• Yet viruses can reproduce, regulate gene
expression and even evolve after infecting
living cells
• Viruses are at the borderline of living and
non-living things
Viruses and Living Cells
• Viruses were not probably the first living
things because they are completely
dependent on living things
• Viruses may have evolved from the
genetic material of living things
Ch. 19 Outline
• 19-3 Diseases caused by bacteria
and viruses
– Bacterial Diseases in Humans
– Controlling Bacteria
– Viral Diseases
– Viroids and Prions
•
Bacterial Diseases in Humans
Pathogen: disease-causing agents
•
Disease can be considered a conflict between the
pathogen and the host
•
Louis Pasteur was the first scientist to show that
bacteria cause a number of human and animal
diseases (The Germ Theory)
Bacterial Diseases in Humans
• Bacteria produce disease in one
of two ways:
1. Damage the cells and tissue of the
infected organism by directly
breaking down the cells for food
2. Release toxins (poisons) that travel
throughout the body and interfere
with normal activity of the host.
• The gram positive bacterium Mycobacterium
tuberculosis is inhaled into the lungs where it
destroys lung tissue
• If bacterium enters a blood vessel, it may travel to
new sights and destroy more tissue
• The Gram positive strain of the Streptococcus
bacterium from Group A causes strep throat by
releasing toxins into the blood stream
• This infection can also cause damage to the heart
valves (rheumatic fever) and kidneys (nephritis).
Streptococcal infections can also cause scarlet
fever, tonsillitis, pneumonia, sinusitis and ear
infections.
• The Gram positive bacterium Corynebacterium
diptheria which causes diptheria infects the tissues
of the throat and releases toxins into the blood
stream
• Diptheria can lead to breathing problems, heart
failure, paralysis, and death
Preventing bacterial disease
• Vaccine: preparation of weakened or killed
pathogen
– Prompts body’s immune system and promts
the body to produce immunity to the disease
– Immunity is the body’s ability to destroy new
pathogens
• Antibiotics: compounds that block the
growth and reproduction of bacteria
Antibiotics
1. Antibiotic-resistant bacteria – bacteria
that have mutated that make them no
longer susceptible to the effects of
antibiotics
a. Genetic mutations for antibiotic resistance
happen spontaneously as a result of errors in
DNA replication
b. Taking Antibiotics eliminates the
susceptible bacteria from the body and
leaves the resistant bacteria, allowing them to
reproduce and pass on their genetic traits
(bacteria reproduce very rapidly!!!)
Antibiotics
c. Antibiotic misuse:
• Usually, if a full course of an Antibiotic is
taken, all the targeted bacteria are killed
and there is no chance for a resistant
strain to evolve;
•
but if the antibiotic is stopped early, the
surviving bacteria will be the ones that
were most resistant to the antibiotic
Antibiotics
2. There are now strains of tuberculosis and
S. aureus that are resistant to multiple
drugs = hard to treat! (Multiple Drug
Resistant Bacteria)
3. Widespread use of antibacterial soaps
can cause antibiotic resistant strains of
bacteria to evolve
• Bacillus Anthracis
(Anthrax)
• Gram positive
• Forms endospores
• Found in soil or on the fur
of animals or in their
digestive tracts
• Dangerous to humans
and animals
• Lung, intestines, and skin
• Respiratory difficulties,
fever, diarrhea, rash
Food Poisoning
•
Staphylococcus
aureus
•
Gram positive
•
causes the most
common type of food
poisoning
•
painful diarrhea and
vomiting
Food Poisoning
•
Salmonella bacteria
(from unprocessed milk,
pork, poultry, eggs)
•
Gram negative
•
cause vomiting,
nausea, and stomach
cramps, which can lead
to fever and death
(especially in the very
young or very old)
Bacteria Table
Preventing bacterial disease
• Controlling Bacteria
– There are various methods used to control
bacterial growth:
• Sterilization kills pathogenic bacteria with heat
• Disinfectants are chemical solution that kills
pathogenic bacteria
• Overuse of disinfectants increase the likelihood that
common bacteria will eventually evolve to become
resistant to them – and therefore much more
dangerous and difficult to kill
Preventing bacterial disease
• Controlling Bacteria
• Food processing allows storage of food in
refrigerators to prevent (delay) spoilage, or cooking
of food at high enough temperatures to kill pathogens
• Canning preserves food for a long time. Food is
heated to a high temperature and placed in sterile
glass jars or metal containers and sealed. Food that
has been properly canned will last almost indefinitely.
• Treating food with everyday chemicals such as salt
(salted meat), vinegar (pickled vegetables), or
sugar (jam) will preserve food.
Viral Disease in Humans
• Like bacteria, viruses produce disease
by disrupting the body’s normal equilibrium.
• Viruses may destroy cells they infect or
cause infected cells to alter their growth and
development
• Unlike bacteria, viral diseases cannot be
treated with antibiotics, but there are some
vaccines against viruses. Vaccines should
be used before an infection begins
Viral Disease in Humans
• Oncogenic or tumor causing viruses may produce
cancer by disrupting the normal controls over cell growth
and division
– Rous Sarcoma Virus in chickens
– Human Papilloma Virus – genital warts; cervical
cancer
Viral Disease in Humans
– Hepatitis B Virus – Liver cancer
– Epstein-Barr Virus – (the virus that causes mono or
even chronic fatigue syndrome) – Burkitt’s lymphoma
Viral Disease in Plants
• Plant viruses pose a serious threat to the foods
we eat
• Viruses have a hard time entering plant cells
because plant cells have a tough cell wall
• Viruses enter plants through tears in leaf tissues,
breaks in stems or roots, or microscopic cell wall
damage
• Most plant viruses are spread by feeding action of
insects
Virus Disease Table
Viroids and Prions
• Scientists have discovered two other virus-like particles
that also cause disease: Viroids and Prions
• Viroids cause disease in plants
• Prions cause disease in animals
• Viroids: Single-stranded RNA molecules that have no
surrounding capsids
– Affect _______ Cells
Viroids and Prions
• Viroids: Single-stranded RNA molecules that
have no surrounding capsids
• It is believed that viroids enter an infected cell and
direct the synthesis of new viroids
• The viroids then disrupt the metabolism of the
plant cell and stunt the growth of the entire plant
Prions
b. Prions – contain no DNA or RNA only protein
i.
Disease-causing proteins are folded into the wrong shape,
which does not allow it to function as it should.
ii.
If a normal prion comes into contact with a disease-causing
one, the normal one will also change its shape so that it is
folded wrong and no longer functions either; in this way, the
disease spreads
iii.
Diseases such as Scrapie (sheep), mad cow disease,
Creutzfeldt-Jacob disease (in humans) are all prion
diseases that can be distributed by eating meat that contains
the malfolded prion.
Prions