Bacteria & Viruses
Biology
Science Department
Deerfield High School
DO NOW:
What are the characteristics of viruses?
Bacteria? What kingdom do each of
these belong? Are they living? Why or
why not?
Biology
Science Department
Deerfield High School
What do you already know?
 What are the differences between
viruses and bacteria?
 Are all bacteria harmful?
 When you get a cold, should you
take an antibiotic to help you get
better?
 What’s the best and easiest thing
to do to avoid getting sick?
Biology
Science Department
Deerfield High School
Bacteria
 Bacteriology is the study of bacteria
 Bacteria are prokaryotic, unicellular
organisms containing DNA and ribosomes.
 Bacteria have ALL the characteristics of living
things.
 Bacteria have the greatest percentage of the
biomass on Earth!
Biology
Science Department
Deerfield High School
Bacterial Structure
 Basic structure of bacteria:
Peptidoglycan*
Cell
wall
Flagellum
Biology
Science Department
Deerfield High School
Cell
Ribosome
membrane
DNA Pili
Bacterial Structure
 Bacteria have three distinct shapes:
spherical
(cocci)
Biology
Science Department
Deerfield High School
rod-shaped
(bacilli)
spiral
(spirilla)
Bacteria
 Bacteria have a variety of important uses:
– Help make interesting food (buttermilk, yogurt, cheese,
sauerkraut, pickles, and olives, etc…)
– Decompose organic matter (recycle nutrients from dead
organisms; break down sewage into simpler compounds)
– Nitrogen fixation (chemically changes nitrogen gas, N2,
into ammonia, NH3, so plants can make amino acids)
– Human health (bacteria on skin help prevent infection &
bacteria in gut helps digest food & make vitamins)
– Biotechnology (used to make antibiotics, insulin, human
growth hormone, vitamins, and other drugs)
Biology
Science Department
Deerfield High School
How Do Pathogenic Bacteria Work?
 Bacteria produce disease in one of two ways:
 Using cells for food: The bacteria break down
healthy cells for food, destroying tissues
 Releasing toxins: The bacteria produce a
toxin (poisonous protein) that is released into
the bloodstream where it can travel
throughout the body, disrupting normal
activity and damaging tissues
Biology
Science Department
Deerfield High School
Bacteria
 A rather vocal minority (less than 1%) of
bacteria cause disease in humans, animals, and
plants.
 Bacteria can cause a variety of diseases:
– Food Poisoning
– Scarlet Fever
– Tuberculosis
– Whooping Cough
– Cholera
– Bacterial Meningitis
– Syphilis
– Pneumonia
– Ulcers
– Leprosy
– Strep Throat
– Tetanus
Biology
Science Department
Deerfield High School
VIDEO CLIP:
Understanding
Bacteria
http://www.youtube.com/watch?v=
yToii3-p-NI
Biology
Science Department
Deerfield High School
Viruses
 Virology is the study of viruses
 Viruses are “biological entities” containing
either DNA or RNA that require another
cell to survive.
 Viruses have some, but not all, of the
characteristics of life.
*So are viruses living or non-living?*
 Viruses seem to exist only to make more
viruses!
Biology
Science Department
Deerfield High School
Biology
Science Department
Deerfield High School
Viral Structure
 All viruses have the same basic structure:
Capsid
(Protein coat)
Biology
Science Department
Deerfield High School
Nucleic
acid core
(DNA or
RNA)
Biology
Science Department
Deerfield High School
How Do Viruses Work?
 In order to replicate and make copies of itself,
viruses need a host cell. Any living cell can
become a host cell (human, animal, plant, and
even bacterial cells!)
 Without a host cell, viruses cannot function (i.e.are harmless!)
 Although any cell can theoretically become a host
cell, specific viruses will only infect specific cells
(EX: HIV will only infect human T cells, a part of your
immune system)
Biology
Science Department
Deerfield High School
How Do Viruses Work?
 Attach: The capsid of the virus binds to receptor
proteins on the surface of a host cell, tricking the
host cell into thinking it’s not a foreign invader.
 Inject: The virus then injects its genetic material
(DNA or RNA) into the host cell.
 Assemble: The viral genes are expressed, turning
the host cell into a virus-making factory.
 Repeat: The host cell eventually bursts, releasing
the hundreds of newly formed viruses to infect VIDEO CLIP:
How Viruses
Work
surrounding cells!
Biology
Science Department
Deerfield High School
lysogenic cycle is a viral replication cycle in which
the virus's nucleic acid is integrated into the host cell's
chromosome, a provirus is formed and replicated each
time the host cell reproduces, the host cell is not
killed until the cycle is activated. At this time the
virus remains quiet for a very long time and it is said
to be hidden.
lytic cycle is a viral replication cycle in which a virus
takes over a host cell's genetic material and uses the
host cell's structures and energy to replicate until the
host cell bursts, killing it. This cycle kills the host cell
almost right away.
Biology
Science Department
Deerfield High School
Biology
Science Department
Deerfield High School
Biology
Science Department
Deerfield High School
Viruses
 Viruses can cause disease in humans, animals, plants,
and even bacteria!
 Viruses can cause a variety of diseases:
– Common cold
– Hepatitis A, B & C
– Herpes
– Mononucleosis
– Warts
– Chickenpox
Biology
Science Department
Deerfield High School
– Polio
– Influenza
– Mumps
– Measles
– Viral Meningitis
– AIDS
VIDEO CLIP:
Viral Disease
Biology
Science Department
Deerfield High School
Protection
 There are a few big ways to protect yourself
against pathogens (disease causing agents)
– Antibiotics (drugs to kill bacteria)
– Antivirals (drugs to treat viruses)
– Vaccination (using your body’s own immune
system to preemptively guard against attack)
Biology
Science Department
Deerfield High School
Antibiotics
 Antibiotics can only be used to treat bacterial
infections!
 Target specific structures on bacteria to kill them.
 First made from a fungus (penicillin), now most
are made artificially.
 Unfortunately, antibiotic resistance (where the
antibiotic doesn’t kill the target bacteria anymore)
is becoming a major problem.
Biology
Science Department
Deerfield High School
Antivirals
 Antivirals can only be used to treat certain viral
infections!
 Does not “kill” or disarm the virus permanently; only
shortens symptoms by 1-2 days.
 Usually only prescribed to patients with life
threatening symptoms or those that have a greater
chance of developing complications (because of their
age or they have a high-risk medical condition).
 Just like antibiotics, there is evidence of antiviral
resistance too!
Biology
Science Department
Deerfield High School
Vaccination
 Vaccines can only be used to prevent infections
(both viral and bacterial) from leading to disease.
 “Trick” your immune system to make antibodies
that destroy foreign “bodies” or particles (such as
bacteria and viruses). Your body remembers how to
make these antibodies when the real thing invades.
 Made from a weakened virus, inactivated virus, or
by using only part of the virus/bacteria itself.
VIDEO CLIP:
Vaccination
Biology
Science Department
Deerfield High School
Biology
Science Department
Deerfield High School
To Review....
 What are the differences between viruses
and bacteria?
 Are all bacteria harmful? Explain.
 When you get a cold, should you take an
antibiotic to help you get better? Why?
 What’s the best and easiest thing to do to
avoid getting sick?
Biology
Science Department
Deerfield High School
http://www.youtube.com/watch?v=
3xRttWuf3wQ
Biology
Science Department
Deerfield High School
Bacteria
Virus
Both
Biology
Science Department
Deerfield High School