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How does your body prevent, and fight
off diseases? (Topic 6.3)
Fathead Minnow Cell infected with epizootic hematopoietic necrosis
virus (EHNV)
Pathogen: organism or virus that causes disease
• Examples: Viruses, bacteria, fungi, protists
How are viruses different than
bacteria?
• How do they get energy?
• Are they living? Why or why not?
• What type of cells do they have?
Why are viruses NOT considered to be
living organisms?
Characteristics of life
Virus
Bacteria
Growth
NO
YES
Metabolism
NO
YES
Mutation
YES
YES
Nucleic Acid
YES
YES
Reproduction
YES (with host) YES
Development
NO
YES
Use Energy
NO
YES
Bacteria are 20x larger than viruses
Virus
Bacteria
Animal Cell
Virus: 0.2 u
Bacteria: 2u
Eukaryotes 50-200u
KINGDOM
BACTERIA
Bacteria on the head of a pin
Anatomy of Bacteria Cells
Characteristics of Bacteria
• Prokaryotic (No nucleus or
membrane bound organelles)
• Cell wall present
• Asexual reproduction by binary
fission (some DNA
recombination through
“conjugation”)
• Heterotrophic (needs to eat
other things) and Autotrophic
(can make its own food)
• Can grow in colonies of trillions
of related individuals
• Not all pathogenic--Curable
VIRUS
VIRUSES
AR BIO
Anatomy of Viruses
Characteristics of Viruses
• Non-living particle
• Made of protein “coat”
and DNA or RNA
• Parasitic: Must live
inside living cells (host)
to reproduce
• Cause of many diseasesnot curable!
• Bacteriophages have DNA
• Retroviruses have RNA
How do pathogens enter the body? Vectors
Vector: an entity that carries and transports the pathogens,
and the disease
• Bacteria: direct body
contact, food or water,
contaminated surfaces
• Viruses: living fluids (Ex:
coughs, sneezes, body
fluids, bites of insects or
animals)
What are the three levels of defense that you have
against pathogens?
1st Level of Defense : Skin & Mucous Membranes
2nd Level of Defense: Macrophages
• Macrophages are “non-specific” because
they will swallow and destroy ANY cell
that is foreign
• Macrophages attempt to get rid of all
pathogenic cells
• Also called “phagocytes”
• Help other white blood cells
(lymphocytes) in the 3rd level of defense
2nd Level of Defense
Inflammatory Response
• Release of histamines to
induce swelling of blood
vessels in infected area
• Increases blood flow to
infected area to bring more
macrophages to infected site
Fever
• Body systems work together to
increase overall body
temperature, and temperature of
infected site
• Higher temperatures make it
harder for bacteria to function
and reproduce
3rd Level of Defense: Production of Antibodies
• Antigen: a protein found on the surface of a cell
that is used for recognition ; different pathogens
have their own antigens
• Antibody: a protein that recognizes a specific
antigen and binds to it ; used to mark pathogens ;
made by B-lymphocytes
• If macrophages are not able to contain the
infection, they will “call in” extra help by embedding
antigens onto their own surfaces.
rd
3
Level of Defense: Production
of Antibodies
• T-helper cells recognize antigens on macrophages
and are “activated” by binding to antigens
• Activation of T-helper cells stimulates B-cells to
produce antibodies (immune response)
3rd Level of Defense – Production of Antibodies
• Activated B-cells clone themselves, cloned cells are now
called “Plasma Cells”
• B-cells and plasma cells continue producing antibodies until
infection is cleared
• After infection is cleared, some plasma cells become
“memory cells” that can be easily activated in case of
future infection ; this is how you develop “immunity”
3rd Level of Defense – Destruction of AntigenAntibody Complexes
• Binding of antibodies to antigens provides macrophages
with specific targets so they only swallow pathogenic cells
Active vs. Passive Immunity
How does your body repair damage to broken blood
vessels? Blood clots (Scabs)
• Process of healing from a
damaged vessel is also
referred to as “haemostasis”
• Purpose is to prevent blood
loss, limit access for
pathogens, and allow for
tissue repair
• Coagulation: process by
which blood clots (and scabs)
are formed – involves a set of
reactions, called the
“coagulation cascade”
Steps of the Coagulation Cascade
1) Clotting factors (proteins) are released
by platelets
2) Clotting factors and platelets form a
plug to prevent blood loss
3) Clotting factors also trigger activation
of enzyme thrombin
4) Activation of thrombin catalyzes
(induces) conversion of fibrinogen to
insoluble fibrin
5) Fibrin strands form mesh that dries
and is maintained until skin tissue is
repaired under damaged site
Coagulation Cascade
Components of a Blood Clot
Why should you know your blood type?
• Antibodies are specific to
certain antigens
• An immune response is
triggered by “non-self
cells” (pathogenic
antigens)
• This is why blood
matches in transplants
and transfusions are
critical (you don’t want
to attack your own
blood/cells!)
Diagnosing Type of Infection Using WBCs
• Neutrophils are a type of
macrophage that
target/swallow bacteria
cells
• T-lymphocytes will target
many viruses
• Blood samples can be
assessed for elevated
levels of a certain WBC
– Ex: elevated levels of
neutrophils suggest a
bacterial infection
Medical Defenses Against Disease
• Viruses:
– Treat with antivirals (inside
body)
– Treat with antiseptics (outside
body)
• Bacteria:
– Treat with antibiotics (inside
body)
– Treat with antiseptics (outside
body)
Antibiotic Treatment for Bacteria
Which antibiotic would you
use to treat this bacteria?
Antibiotics (“against life”): kill
bacteria by attacking internal
metabolic processes
•Grow bacteria on a nutrient
agar plate
•Place antibiotic discs on plate
•Measure area where bacteria
are killed (did not grow) This is
the Zone of Inhibition
•The Zone of Inhibition which is
the largest shows which
antibiotic will be the most
effective against the infection
How HIV Infects Cells
1) HIV virus binds to, and
moves inside T-helper
cells
2) HIV inserts its own
genetic material into Tcells DNA, changing
directions for the cell
3) HIV uses T-cells
organelles to build new
viruses
4) Viruses get released
and go infect other cells
Image source: https://aidsinfo.nih.gov/images/factsheet/HIV-Lifecycle-03-f.jpg