Download Ch. 19 Bacteria and Viruses

Ch. 19
Biology
Virus
Bacterium
Animal
cell
0.25 µm
Animal cell nucleus
 Bacteria
are
prokaryotes with
cells much smaller
and more simply
organized than
those of eukaryotes
 Viruses are smaller
and simpler than
bacteria



Tobacco mosaic disease
stunts growth of tobacco
plants and gives their
leaves a mosaic coloration
In the late 1800s,
researchers hypothesized
that a particle smaller than
bacteria caused the disease
In 1935, Wendell Stanley
confirmed this hypothesis
by crystallizing the
infectious particle, now
known as tobacco mosaic
virus (TMV)
 Viruses
are particles of nucleic acid,
protein, and in some cases, lipids.
 Viruses can replicate only by infecting
living cells.
Copyright Pearson Prentice Hall
 Viruses
differ widely
in terms of size and
structure.
 All viruses enter
living cells and use
the infected cell to
produce more
viruses.
Copyright Pearson Prentice Hall
composed of a core of
DNA or RNA
surrounded by a
protein coat.
• A capsid is the virus’s
protein coat.
Copyright Pearson Prentice Hall
http://img.sparknotes.com/figures/2/285caff64361a769a0850014b87c228c/structure.gif
• A typical virus is
 DNA
viruses
• Genome is DNA
 RNA
viruses
• Genome is RNA
• Smaller than DNA viruses
• Lack of proofreading—leads to  evolution rate



Capsid proteins bind
to receptors on the cell
surface and “trick” the
cell into allowing it
inside.
Once inside, viral
genes are expressed
and the cell
transcribes and
translates them into
viral capsid proteins.
The host cell may
makes copies of the
virus, and be
destroyed.
http://www.flutrackers.com/forum/attachment.php?attachmentid=326&d=1148840493
Copyright Pearson Prentice Hall
 Most
viruses are
highly specific to the
cells they infect.
 Viruses that infect
bacteria are called
bacteriophages.
Copyright Pearson Prentice Hall
 Viruses
that infect
bacteria
 Set in motion a
genetic takeover of
bacteria, such as
Escherichia coli
 Once
the virus is inside the host cell, two
different processes may occur.
• Some viruses replicate immediately, killing the
host cell (lytic cycle).
• Others replicate, but do not kill the host cell
immediately (lysogenic cycle).
Copyright Pearson Prentice Hall
 Lytic
Infection
• In a lytic infection, a virus enters a cell, makes
copies of itself, and causes the cell to burst.
Copyright Pearson Prentice Hall
 First, the
bacteriophage
injects DNA into a
bacterium.
 The bacteriophage
DNA forms a circle.
 Phage DNA takes
control and has cell
make more phage
DNA and proteins
Copyright Pearson Prentice Hall
 Phage
DNA and
proteins are
assembled into new
bacteriophages
 The cell lyses
(bursts) and releases
bacteriophages
Copyright Pearson Prentice Hall
 Lysogenic
Infection
• Other viruses cause lysogenic infections in
which a host cell makes copies of the virus
indefinitely.
• In a lysogenic infection, a virus integrates its
DNA into the DNA of the host cell, and the viral
genetic information replicates along with the
host cell's DNA.
Copyright Pearson Prentice Hall
• A lysogenic infection
begins the same way
as a lytic infection.
• The bacteriophage
injects DNA into a
bacterium.
• The bacteriophage
DNA forms a circle.
• The viral DNA
embedded in the
host's DNA is called a
prophage.
Copyright Pearson Prentice Hall
• Bacterial cell can
divide normally
through binary fission
(copying the phage
DNA as well).
• Phage DNA can exit
the bacterial
chromosome and then
enter the lytic cycle.
Copyright Pearson Prentice Hall
 Retroviruses
contain RNA as their
genetic information.
 When retroviruses infect cells, they make
a DNA copy of their RNA.
 This DNA is inserted into the DNA of the
host cell.
Copyright Pearson Prentice Hall
A
retrovirus’ genetic
information is copied
backward—from RNA
to DNA.
 The virus that causes
AIDS is a retrovirus.
• Human
Immunodeficiency
Virus (HIV)
Copyright Pearson Prentice Hall
 Viruses
are NOT living things.
• Viruses are not made of cells.
• Viruses must infect a living cell in order to grow
and replicate.
• They have no metabolism--use host’s respiration,
nutrition, and all other functions of living things.
Copyright Pearson Prentice Hall
 Viruses
have many of the characteristics
of living things.
 After infecting living cells, viruses can
replicate, regulate gene expression, and
even evolve.
Copyright Pearson Prentice Hall
 Because
viruses are dependent on living
things, it seems likely that viruses
developed after living cells.
 The first viruses may have evolved from
genetic material of living cells.
 Viruses have continued to evolve over
billions of years.
Copyright Pearson Prentice Hall
Viruses that contain RNA as their genetic
information are known as
a)
b)
c)
d)
prions.
oncoviruses.
retroviruses.
bacteriophage.
Copyright Pearson Prentice Hall
The first type of virus to be studied was the
a)
b)
c)
d)
bacteriophage.
tobacco mosaic virus.
influenza virus.
AIDS virus.
Copyright Pearson Prentice Hall
Which of the following statements about viruses is
true?
a) Viruses appear similar to bacteria when studied with
a light microscope.
b) Viruses display the essential characteristics of living
things.
c) Viruses can reproduce independently if they contain
DNA.
d) Viruses cannot reproduce unless they infect a living
cell.
Copyright Pearson Prentice Hall
A virus integrates its DNA into the DNA of the host
cell but remains inactive for a while in
a)
b)
c)
d)
a lytic infection.
a lysogenic infection.
neither a lytic nor a lysogenic infection.
retroviral infection.
Copyright Pearson Prentice Hall
Retroviruses are considered unique because
a)
b)
c)
d)
they have RNA in their capsid and not DNA.
they have DNA in their capsid and not RNA.
after infection of a host cell, their RNA makes DNA.
after infection of a host cell, their DNA makes RNA.
Copyright Pearson Prentice Hall
Ch. 19
Biology
 Bacteria
and viruses are everywhere in
nature, but only a few cause disease.
 Disease-causing agents are called
pathogens.
Copyright Pearson Prentice Hall
 Bacterial
Disease in Humans
 Growth of pathogenic bacteria disrupts the body’s
equilibrium by interfering with its normal activities
and producing disease.
Copyright Pearson Prentice Hall
 Bacteria
produce disease in one of two
general ways.
• Some bacteria damage the cells and tissues
of the infected organism directly by breaking
down the cells for food.
• Other bacteria release toxins (poisons) that
travel throughout the body interfering with
the normal activity of the host.
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
 Many
bacterial diseases can be
prevented by vaccines.
 A vaccine is a preparation of weakened
or killed pathogens.
 When injected into the body, a
bacteria/virus may prompt the body’s
immunity to the disease.
 Immunity is the body's ability to destroy
new pathogens.
Copyright Pearson Prentice Hall
• If infection occurs, drugs
can be used to destroy
bacteria.
• These drugs include
antibiotics, which are
compounds that block
the growth and
reproduction of bacteria.
• A reason for increased
human life expectancy is
an increased
understanding of how to
prevent and cure
bacterial infections.
http://raleighway.com/who/c9b_ecoli_kirby.jpg
Copyright Pearson Prentice Hall
• There are various methods used to control bacterial
growth, including:
 sterilization
 disinfectants
 food processing
Copyright Pearson Prentice Hall
• Sterilization by Heat
 Sterilization destroys bacteria by subjecting them to
great heat.
 Most bacteria are killed by prolonged high
temperatures.
Copyright Pearson Prentice Hall
• Disinfectants
 Disinfectants are chemical solutions that kill
pathogenic bacteria.
 They are used to clean rooms where bacteria may
flourish.
Copyright Pearson Prentice Hall
• Food Storage and Processing
 Bacteria can cause food to spoil.
 Refrigerated food stays fresh longer because the
bacteria will take longer to multiply.
 Boiling, frying, or steaming can sterilize certain foods.
 Heat kills the bacteria
Copyright Pearson Prentice Hall
 Viruses
produce disease by disrupting
the body's normal equilibrium.
 Viruses can attack and destroy certain
cells in the body, causing symptoms of
the disease.
 Other viruses cause infected cells to
change patterns of growth and
development.
Copyright Pearson Prentice Hall
 Viral
diseases cannot be treated with
antibiotics.
 Vaccines are often the best protection
against most diseases.
 Most vaccines work only if used before
an infection begins.
 Symptoms may be treated with over-thecounter medicines.
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
 Viral
Disease in Plants and Animals
 Viruses produce serious animal diseases including
foot-and-mouth disease.
 Many viruses infect plants.
 These viruses pose a serious threat to many crops.
Copyright Pearson Prentice Hall
 Antibiotics
don’t work—no metabolic
reactions to interfere with
 Vaccines—harmless derivatives of
pathogenic microbes that stimulate the
immune system to mount defenses against
the actual pathogen
• Parts of viruses, modified or killed viruses are
injected into the body
• Allows immune system to make antibodies
against specific markers on the viral coat
 HIV mutates too fast for immune system to keep up with

Influenza, also known as the flu,
is a contagious disease that is
caused by the influenza
virus. It attacks the respiratory
tract in humans (nose, throat,
and lungs). The flu is different
from a cold. Influenza usually
comes on suddenly and may
include these symptoms:
• Fever
• Headache
• Tiredness (can be extreme)
• Dry cough
• Sore throat
• Nasal congestion
• Body aches
 Emerging
viruses are those that appear
suddenly or suddenly come to the
attention of scientists
 Severe acute respiratory syndrome (SARS)
appeared in China
 Outbreaks of “new” viral diseases in
humans are usually caused by existing
viruses that expand their host territory
Young ballet students in Hong
Kong wear face masks to
protect themselves from the
virus causing SARS.
The SARS-causing agent is a
coronavirus like this one
(colorized TEM), so named for
the “corona” of glyco-protein
spikes protruding form the
envelope.
Copyright Pearson Prentice Hall
Biologists know that bacteria can cause human
disease by
a) entering cells and using the cell to make new
bacteria.
b) producing toxic substances that interfere with normal
cell function.
c) decomposing the remains of dead organisms.
d) changing atmospheric nitrogen into nitrogen
compounds.
Copyright Pearson Prentice Hall
A process that destroys bacteria by subjecting
them to great heat is known as
a)
b)
c)
d)
refrigeration.
sterilization.
pickling.
boiling.
Copyright Pearson Prentice Hall
Which of the following diseases is transmitted by
a mosquito bite?
a)
b)
c)
d)
influenza
measles
West Nile virus
chickenpox
Copyright Pearson Prentice Hall
The best way to combat viral diseases is
a)
b)
c)
d)
to use antibiotics.
to treat individual symptoms.
to use preventive vaccines.
to let the disease “cure itself.”
Copyright Pearson Prentice Hall