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Bacteria and Viruses
HIV Virus
Generalized Bacterial Cell
Yersinia pestis
Bacterial Facts
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All bacteria are prokaryotes: they lack
membrane-bound organelles within their
cells.
All bacteria are microscopic in size.
Fossils of bacteria have been found that
are 3.5 billion years old.
The oldest fossils of eukaryotic cells are
2.5 billion years old.
Bacterial Evolution and Classification
Bacteria are separated into two kingdoms:
Archaebacteria and Eubacteria
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Archaebacterial cells have cell
walls that lack the chemical
peptidoglycan.
Archaebacterial genes have
introns and exons, like the genes
of eukaryotes.
Archaebacteria are more ancient
than eubacteria.
Today, many archaebacteria can
only exist in extreme
environments like that of the
ancient Earth.
Archaebacteria probably evolved
from an earlier ancestor that led
to all of the eukaryotes.
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Most bacteria today are
eubacteria.
Eubacterial cells have cell walls
that contain the chemical
peptidoglycan.
Eubacterial genes lack introns
and exons, and are unlike the
genes of eukaryotes.
Most eubacteria can be grouped
into two groups: Gram + or
Gram -.
Although some eubacteria cause
diseases, many more are helpful
to the environment.
Kingdom Archaebacteria
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Methanogens are archaebacteria
that harvest energy by changing
H2 and CO 2 into methane gas.
They are anaerobic
chemoautotrophs.
They live in the mud at the
bottom of swamps and in
sewage and in the large
intestines of many vertebrates
including humans.
Extreme halophiles live in very
salty environments like the Great
Salt Lake and the Dead Sea.
They are also chemoautotrophs,
in that they use salt to produce
ATP.
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Thermoacidophiles are
archaebacteria that thrive in very
acidic environments (a pH less
than 2) with very high
temperatures (up to 110oC), such
as volcanic vents on land or in
deep water near cracks in the
ocean floor.
Thermoacidophiles can be found in
the hot springs in Yellowstone.
Kingdom Eubacteria
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I.
Most bacteria are eubacteria, II. Bacteria are also classified by
which exist in many shapes
how they group together: two
and sizes. They also have
together (diplo-), chains of
metabolic and genetic
bacteria (strepto-), or clusters
differences.
(staphlo-)
Eubacteria are classified
according to four basic criteria.
Most eubacteria come in one
of three basic shapes: rodshape (bacillus), round
(coccus), or spiral (spirilla).
Bacteria Types: Bacillus
III.
IV.
Bacteria can be classified according to
the composition of their cell walls as
Gram + or Gram -.
Bacteria can be classified according to
their type of respiration: obligate
aerobes need O2, obligate
anaerobes are poisoned by O2, and
facultative anaerobes can exist in
the presence or the absence of O2.
Some Phyla of Eubacteria
Phylum
Shape
How it
moves
Importance
Type of metabolism
Gram
stain
Cyanobacteria
Bacilli,
cocci
Gliding,
some
don’t
move
Filled Earth’s
atmosphere with
oxygen.
Aerobic,
photosynthetic
autotrophs
Gram -
Spirochetes
Spirals
Corkscrew
motion
One type of
spirochete causes
syphilis.
Aerobic and anaerobic
heterotrophs
Gram -
Gram +
bacteria
Bacilli,
cocci
Flagella,
some
don’t
move
Many cause
diseases like tooth
decay, but some
are used to
culture yogurt and
cheese.
Aerobic and anaerobic
heterotrophs and
photosynthetic
autotrophs
Gram +
Proteobacteria
Bacilli,
cocci,
spirals
Flagella,
some
don’t
move
Enteric bacteria
live in intestinal
tracts, nitrogenfixing bacteria,
chemoautotrophs
Aerobic and anaerobic
heterotrophs, unusual
metabolism, some are
photosynthetic
autotrophs
Gram -
Photosynthetic Bacteria
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Most of the world’s
photosynthesis is carried
out by bacteria.
There are four kinds of
photosynthetic bacteria,
classified according to the
photosynthetic pigment
they contain.
Green-sulfur bacteria and
purple-sulfur bacteria are
anaerobic. They use sulfur
containing compounds like
H2S as an electron source
instead of H2O. They
produce elemental sulfur
instead of O2.
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Purple non-sulfur bacteria
use organic compounds like
acids for photosynthesis.
One group of
photosynthetic bacteria is
especially important. The
cyanobacteria are
responsible for the present
amounts of O2 in the
atmosphere.
Several types of Cyanobacteria
Chemoautotrophic Bacteria
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Chemoautotrophs do not get
their energy from the sun.
Instead, they get energy by
removing high-energy electrons
from inorganic molecules like
ammonia (NH3), methane (CH4),
or hydrogen sulfide (H2S).
Chemoautotrophic bacteria like
Nitrobacter or Nitrosomonas live
in the soil and are important to
the environment and to
agriculture.
These bacteria are important in
the process of nitrification,
making atmospheric N2 into
nitrates, which plants need for
growth.
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Nitrogen is needed by all living
things because it is a component
of amino acids, which are the
building blocks of protein.
Without these nitrifying bacteria,
plants and other living things
could not take nitrogen into their
bodies, and thus could not
survive.
Nitrobacter,
shown as red
or orange
amid other
bacteria.
Heterotrophic Bacteria
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Most bacteria are heterotrophic. 
They get their organic molecules
from other living things.
Along with fungi, heterotrophic
bacteria are the main
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decomposers in the living world.
Heterotrophic bacteria are crucial
to the recycling of molecules in 
the living world. They break
down the bodies of dead
organisms into small molecules 
that can be absorbed and used
by other living things.
Other activities of heterotrophic
bacteria can be helpful or harmful
to other living things.
More than half of our antibiotics
are produced by various species
of the heterotrophic bacterial
genus Streptomyces.
Another genus of heterotrophic
bacteria, Staphlococcus, secretes a
toxic substance into food that causes
nausea, vomiting, and diarrhea.
Species of the bacteria Rhizobium live
symbiotically in nodules on the roots
of a type of plants called legumes.
These plants include beans and peas
peanuts, alfalfa, and clover, among
others.
The plant nodules make an anaerobic
environment for the Rhizobium and
the bacterium fixes nitrogen for use
by the plant. When these crops are
planted, they replenish the soil’s
nitrogen used by other crops.
Disease-Causing Bacteria
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Bacteria can also be parasitic.
When parasitic bacteria invade your
body, they can secrete toxic
substances or attack your cells. You
now have a “disease.”
Pathogenic bacteria cause a host of
diseases. Many of these can be
treated with antibiotics, although
many bacteria are becoming
antibiotic resistant.
Antibiotics are substances produced
by other bacteria or by fungi that
interfere with the growth or
reproduction of disease-causing
bacteria. Antibiotics are useless
against viruses.
Many bacterial diseases have
affected the course of human
history. Some of these are bubonic
plague, cholera, and typhoid fever.
Bacteria and Disease
Disease
Pathogen
Areas Affected
How Spread?
Botulism
Clostridium bolulinum
Nerves
Improperly preserved
foods
Cholera
Vibrio cholerae
Intestines
Contaminated water
Dental caries
Streptococcus mutans, S.
sanguis, and S. salivarius
Teeth
Bacteria enter the mouth
from the environment
Gonorrhea
Neisseria gonorrhaeae
Urethra, fallopian tubes,
epididymis
Person-to-person by
sexual contact
Lyme disease
Borrelia burgdorferi
Skin, joints, heart
Tick bite
Rocky Mt. Spotted
Fever
Rickettsia ricketsii
Blood, skin
Tick bite
Salmonella food
poisoning
Salmonella
Intestine
Contaminated water and
food
Strep throat
Streptococcus pyogenes
Upper respiratory tract,
blood, skin
Person-to-person by
sneezes, coughs, or
direct contact
Tetanus
Clostridium tetani
Nerves at synapses
(junctions between nerves
Contaminated wounds
Tuberculosis
Mycobacterium tuberculosis
Lungs, bones, other internal
organs
Person-to-person by
coughs
Chart from Modern Biology, Holt, Rinehart, Winston
Comparing Bacterial Cells to
Eukaryotic Cells
Bacterial Cell
Eukaryotic Cell
Internal
They lack membrane-bound They have membrane-bound
Compartments organelles or membrane
organelles or membrane systems.
systems.
Cell Size
Most are 1 micrometer in
diameter (1 µm).
Most are at least 10 µm in diameter.
Multicellularity
All are unicellular.
Some are unicellular, but many are
multicellular.
Chromosomes
One circular piece of DNA
Linear chromosomes are made of
DNA combined with histone proteins.
Cell Division
Binary fission only
Nucleus divides by mitosis before
cytokinesis.
Flagella
Made of one protein fiber
that spins like a corkscrew
Made of groups of microtubules that
contract to whip back and forth
Metabolic
Diversity
Have many metabolic
All are aerobic.
pathways that eukaryotes
lack (anaerobic metabolism)
Viral Structure
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All viruses have a nucleic acid, either
DNA or RNA, surrounded by a
protein cover, called a capsid. They
do not have cytoplasm inside the
capsid and are not made of cells.
Many viruses that infect animals also
have an outer membrane called the
envelope that surrounds the capsid.
The envelope is made of proteins,
lipids, and glycoproteins that help it
attach to the cell membrane of the
host cell.
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Viruses differ greatly in their
appearance. Some are just
one nucleic acid molecule
inside a protein capsid made of
just one protein.
More complex viruses contain
several pieces of DNA or RNA,
and the capsid can be made of
several different proteins.
Viruses are either helical in
shape (and look like rods) or
are polyhedral. The usual
polyhedron is an isacohedron
made of 20 triangular faces.
Bacteriophage viruses have a
complex shape with a
polyhedral head attached to a
helical tail.
Are Viruses Alive? What do you think?
Biologists have agreed upon several characteristics of living
things.
 Viruses are not made of cells. Viruses
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Cellular organization: All
living things are made of
cells.
Metabolism: All living things
use energy to grow, move,
and perform other functions.
Homeostasis: All living things
control their internal
conditions even when
external conditions change.
Reproduction: All living things
produce offspring.
Heredity: All living things use
DNA as their genetic
material.
Viruses do not perform
homeostasis.
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are composed of two basic parts: a
nucleic acid and a protein coat.
Viruses can be crystallized.
Viruses do not use energy or perform
any other functions of living things
unless they are inside of a living thing
and antibiotics are useless against
them.
Viruses can only “reproduce” when
inside of a living thing.
Viruses do contain a nucleic acid.
Some of them contain DNA and some
contain RNA.
Since viruses do not have many of the
characteristics of life, they are not
considered to be alive.
Viral Replication
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Viruses can only be replicated
by infecting a cell and using
the cell’s enzymes and other
molecules to build new
viruses. They cannot
reproduce by themselves.
Bacteriophages are viruses
that infect bacteria. Their
replication patterns are similar
to the patterns of viruses that
cause such human diseases as
colds, measles, and AIDS.
Bacteriophage
viruses
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Some viruses are described as
virulent because they cause disease.
These viruses attach to a host cell,
hijack its DNA, and after the host
has produced new viruses, it bursts.
The newly released viruses are free
to infect other host cells. This cycle
of immediate host destruction is
called a lytic cycle.
Viruses that infect host cells without
killing them immediately are in a
lysogenic cycle. They can stay inside
their host cells for years. AIDS is
caused by the HIV virus, which can
remain in a lysogenic cycle for up to
10 years before causing disease
symptoms.
Viruses and Disease
Disease
Symptoms
Vaccine?
Mode of Transmission
Chickenpox
Blisters, painful rash, fever
Yes
Air currents
Measles
Blotchy rash, respiratory
congestion, high fever
Yes
Air currents
Rubella
Rash, swollen glands
Yes
Air currents
Mumps
Painful swelling in salivary
glands
Yes
Air currents
Smallpox
Blisters, lesions, fever,
malaise, often fatal
Yes
Air currents
Infectious
hepatitis
Fever, chills, nausea,
swollen liver, jaundice,
painful joints
Yes
Contaminated food or water
Polio
Headache, stiff neck,
possible paralysis
Yes
Contaminated food or water
AIDS
Immune system failure,
fatal
no
Sexual contact, contaminated
blood products or hypodermic
needles
Chart from Biology: Principles and Explorations, Holt, Rinehart, and Winston