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31.1 Pathogens and Human Illness
KEY CONCEPT
Germs cause many diseases in humans.
31.1 Pathogens and Human Illness
Germ theory proposes that microscopic particles or
microorganisms cause certain diseases.
– proposed by Louis Pasteur
– led to rapid advances in understanding disease
31.1 Pathogens and Human Illness
• Supported by Koch’s postulates.
• Four conditions that prove a pathogen causes a disease
• Particles are disease-causing agents called pathogens.
31.1 Pathogens and Human Illness
There are different types of pathogens.
• Bacteria are single-celled
organisms.
– cause illness by
destroying cells
– release toxic chemicals
31.1 Pathogens and Human Illness
• Viruses are genetic
material surrounded by
a protein coat.
– force host cells to
make more viruses
– very small
31.1 Pathogens and Human Illness
• Fungi can be multicellular or single-celled.
– take nutrients from host cells
– occur in warm and damp places
31.1 Pathogens and Human Illness
• Protozoa are single-celled organisms.
– use host cells to complete their life cycles
– take nutrients from host cell
31.1 Pathogens and Human Illness
• Parasites are multicellular organisms.
– grow and feed on a host
– possibly kill the host
31.1 Pathogens and Human Illness
• Different pathogen cause common infectious diseases.
31.1 Pathogens and Human Illness
Pathogens can enter
the body in different
ways.
Pathogens are
spread by
Direct contact:
requires touching
an infected
individual
Kissing
sexual intercourse
Indirect contact:
does not require
touching an
infected individual
Hand shaking
touching an
infected
surface
breathing in
infected
air
18.2 Viral Structure and Reproduction
KEY CONCEPT
Viruses exist in a variety of shapes and sizes.
18.2 Viral Structure and Reproduction
Viruses differ in shape and in ways of entering host
cells.
• Viruses have a simple structure.
– genetic material
– capsid, a protein shell
– maybe a lipid envelope, a protective outer coat
enveloped
(influenza)
capsid
nucleic acid
lipid
envelope
helical
(rabies)
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
polyhedral
(foot-and-mouth
disease)
surface
proteins
capsid
nucleic acid
18.2 Viral Structure and Reproduction
• Bacteriophages infect bacteria.
capsid
DNA
tail sheath
tail fiber
18.1 Studying Viruses and Prokaryotes
What are viruses?
Are viruses living?
Why not?
18.1 Studying Viruses and Prokaryotes
Viruses differ from living cells.
• Living things
– Reproduce on their
own
– Use nutrients and
energy
– Grow and develop
– Respond to the
environment
• Viruses are not living
because:
1 nanometer
– Don’t carry
out (nm) = one
billionth of a meter
respiration, grow, or
develop
100 nm
– Can’t reproduce on
viroids
their own
5-150 nm
prokaryotics cells
200-10,000 nm
viruses
50-200 nm
prion
2-10 nm
18.1 Studying Viruses and Prokaryotes
Viruses, bacteria, viroids, and prions can all cause
infection.
• Any disease-causing agent is called a pathogen.
1 nanometer (nm) = one
billionth of a meter
100 nm
eukaryotics cells
10,000-100,000 nm
viruses
50-200 nm
prokaryotics cells
200-10,000 nm
viroids
5-150 nm
prion
2-10 nm
18.1 Studying Viruses and Prokaryotes
Differences between the types of small particles
Particle or
Organism
Description
Prion
Made of proteins only; cause other proteins to fold incorrectly
which makes them NOT work
No cure; body can not defend against proteins; MAD COW disease
Viroid
Single stranded DNA or RNA & NO protein coat
Disease of plants that passes through seeds or pollen
Virus
Made of DNA or RNA with a protein coat
Must have a host cell to reproduce
FLU, HIV, SARS
Bacteria
Living cell contains DNA & RNA
Reproduce easily on their own
Salmonella, E coli
18.1 Studying Viruses and Prokaryotes
Differences between the types of small particles
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– bacteriophages pierce host cells and inject their DNA
into the cell
colored SEM; magnifications:
large photo 25,000; inset 38,000x
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– viruses of eukaryotes enter by endocytosis
18.1 Studying Viruses and Prokaryotes
• Viruses enter cells in various ways.
– viruses of eukaryotes also fuse with membrane
18.2 Viral Structure and Reproduction
Viruses cause two types of infections.
• A lytic infection causes the host cell to burst.
host bacterium
The bacterophage attaches
and injects it DNA into a host
bacterium.
The host bacterium breaks apart,
or lyses. Bacteriophages are able
to infect new host cells.
The viral DNA
forms a circle.
The viral DNA directs the host
cell to produce new viral parts.
The parts assemble into new
bacteriophages.
The virus may enter the
lysogenic cycle, in which the
host cell is not destroyed.
18.2 Viral Structure and Reproduction
• A lysogenic infection does no immediate harm.
The prophage may leave the
host’s DNA and enter the
lytic cycle.
The viral DNA is called a prophage
when it combines with
the host cell’s DNA.
Many cell divisions produce a
colony of bacteria infected
with prophage.
Although the prophage is not
active, it replicates along with
the host cell’s DNA.
31.2 Immune System
KEY CONCEPT
The immune systems consists of organs, cells, and
molecules that fight infections. The immune system is
the body system that fights off infection and pathogens
31.2 Immune System
Many body systems protect you from pathogens.
• Many other tissues and systems help the immune system.
– Skin is a physical barrier to infection.
– Mucous membranes trap pathogens entering the body.
– The circulatory system transports immune cells.
31.2 Immune System
Cells and proteins fight the body’s infections.
• White blood cells attack infections inside the body.
– Phagocytes engulf and destroy pathogens.
– T cells destroy infected cells.
– B cells produce antibodies.
31.2 Immune System
• Three types of proteins fight off invading pathogens.
– Complement proteins weaken pathogen membranes.
– Antibodies make pathogens ineffective.
– Interferons prevent viruses from infecting healthy cells.
antibody
pathogens
31.2 Immune System
Immunity prevents a person from getting sick from a
pathogen.
Passed through genetics
Acquired after the body
Or through mother’s milk
undergoes a specific
immune response
Prevent future illness if the body becomes
infected
18.3 Viral Diseases
KEY CONCEPT
Some viral diseases can be prevented with vaccines.
18.3 Viral Diseases
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
18.3 Viral Diseases
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
– influenza
18.3 Viral Diseases
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
– influenza
– SARS
18.3 Viral Diseases
Viruses cause many infectious diseases
• There are many examples of viral infections.
– HIV
• The body has
natural
defenses
against viruses.
HIV-infected
white
blood cell
18.3 Viral Diseases
Vaccines are made from weakened pathogens.
• A vaccine stimulates the body’s own immune response.
• Vaccines prepare the immune system for a future attack.
• Vaccines are the only way to control the spread of viral
disease.
18.6 Bacterial Diseases and Antibiotics
KEY CONCEPT
Understanding bacteria is necessary to prevent
and treat disease.
18.6 Bacterial Diseases and Antibiotics
Some bacteria cause disease.
• Bacteria cause disease by invading tissues or making
toxins.
• A toxin is a poison released by an organism.
18.6 Bacterial Diseases and Antibiotics
• Normally harmless bacteria can become destructive.
– may colonize new tissues
18.6 Bacterial Diseases and Antibiotics
• Normally harmless bacteria can become destructive.
– immune system may be lowered
31.4 Immunity and Technology
KEY CONCEPT
Living in a clean environment and building immunity
help keep a person healthy.
31.4 Immunity and Technology
Many methods are used to control pathogens.
• Antibiotics and antiseptics cause pathogens to burst.
31.4 Immunity and Technology
• Antiseptics kill pathogens outside of the body.
– do not target specific pathogens
– examples include vinegar and soap
• Antibiotics kill pathogens inside the body.
– target one specific bacterium or fungus
– not effective against viruses
– Vaccines help to identify and make viruses ineffective
– Given to a person to prevent illness
– Can be made of dead or weakened virues
31.4 Immunity and Technology
• Antibiotic resistance can cause medicines to become
ineffective.
– Some bacteria in a population have genes that make
them immune to antibiotics.
– These bacteria spread the gene, making the antibiotics
useless.
A bacterium carries
genes for antibiotic
resistance on a plasmid.
A copy of the plasmid is transferred
through conjugation.
Resistance is quickly
spread through
many bacteria.
31.4 Immunity and Technology
Vaccines artificially produce acquired immunity.
• Vaccines also control pathogens and disease.
– given to prevent illness
– contain the antigen of a weakened pathogen
31.4 Immunity and Technology
• Vaccination provides immunity.
– stimulates a specific
immune response
memory B cells
– causes memory
cells to be produced
– allows immune
system to respond
quickly to infection
– has such a fast
response, a person
will not get sick
Antigens in a vaccine
trigger an immune response,
and memory B cells are
made.
1
2
3
A memory B cell is
stimulated when the real
pathogen binds to it.
The B cell quickly activates
and makes antibodies that
fight the pathogens before
you get sick.