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Chapter 16
Bacteria and Viruses
Prokaryotes
Or 100 Trillion Friends That
You Didn’t Know You Had
Bacteria
• Were once included in Kingdom
Monera (which doesn’t exist anymore)
• Now 2 separate groups:
–Archeabacteria
–Eubacteria
Archaebacteria—cell wall lacks peptidoglycan
--contains membrane lipids (fats) not found in
any other living things.
--Live in extremely harsh environments
Ex.-Oxygen-free locations (thick mud,
digestive tract of animals, Great Salt
Lake, hot springs, etc)
Biologists refer to Archeaebacteria as
“extremophiles” (Lovers of the extremes)
Thermophiles: Heat lovers; live in hot springs of
Yellowstone National Park or deep sea ocean
vents
Halophiles: Salt lovers; thrive in areas like Great
Salt Lake
Methanogens: Oxygen free environments; such
as mud at bottom of lakes and swamps where
they produce “swamp gas” (methane)
Eubacteria—usually surrounded by a cell
wall (made of peptidoglycan—a carbohydrate)
that protects the cell from injury and
determines its shape
--As a result (of the protective cell wall), these
bacteria can live almost anywhere. (fresh
water, salt water, on land, on or in human
body, etc)
E. coli, a Typical Eubacterium
Pili
Flagellum
DNA
Prokaryotes are identified by:
1. SHAPE
Bacilli:
rod-shaped
prok’s
Cocci:
Spherical
prok’s
Spirilla:
Spiral and
corkscrewshaped
prok’s
2.Cell Walls
Two different kinds in Eubacteria.
•Completely composed of peptidoglycan (thick)
•Less peptidoglycan and an additional
outer membrane (thin)
How can you tell the difference??
Gram Staining: Test with violet and pink dyes.
Under a microscope, if the bacteria is purple they are
Gram-Positive; This is because of extra thick cell wall
(lots of peptidoglycan)
If bacteria is pink it is Gram-negative. (not a lot of
peptidoglycan)
Gram Staining Procedure
How is Gram Staining Useful?
• Doctors use Gram staining to identify bacteria
in order to prescribe the correct antibiotics.
Some antibiotics only work against Grampositive bacteria.
3. Movement
Some move, some don’t (non-motile)
If they do move, how do they move?
-flagella (might be scattered all over the cell,
or in one area)
-pili (short projections that help bacteria stick
to each other and to surfaces)
-“spiral” or “snake” forward
-glide a slime like material they secrete
Metabolic Diversity
Ways bacteria obtain energy!
(modes of nutrition)
Chemoheterotrophs-must take in organic
molecules for both energy and supply of
carbon
Photoheterotroph-perform photosynthesis for
energy, but must take in organic compounds
as a carbon source
Photoautotrophs-use light energy to convert
CO2 and H2O to carbon compounds and O2
Chemoautotrophs-make organic carbon
molecules from CO2 (don’t require light)
Growth and Reproduction
- Bacteria will divide very quickly if their
environment is favorable
- Binary Fission: Asexual reproduction
- offspring are genetically identical to parent
- no new genetic combinations
- under ideal conditions can occur every 20 min
- creates large numbers of bacteria in a short time
Jeff Simmonds - The Multiplication Song
http://www.youtube.com/watch?v=5Xi2Nc1UicQ
• Each spot represents
a single bacterial
cell that reproduced
by binary fission to
produce millions of
genetically identical
cells.
• Genetically identical,
good or bad?
Exchanging Genetic Information
• Bacterial cells need to be able to exchange genetic
information
- creates new genetic combinations which increases the
ability of the bacteria to survive
• Bacteria have 3 methods for exchanging DNA
-Transduction – viruses carry DNA from one bacterial
cell to another
-Transformation – bacteria can absorb “naked” DNA
released by dead bacteria from
the environment
- Conjugation – two bacteria join at a conjugation
bridge, one bacteria passes on a
copy of its plasmid or chromosome
Exchanging Genetic Information
Transduction – DNA is carried from one
bacteria to another by a virus
Transformation: Bacteria absorb
“naked” DNA from the
environment
Conjugation
Conjugation- one cell passes a copy of
its plasmid or chromosome to another
Donor Cell
Recipient
Cell
A special pilus forms
a connection called
a conjugation bridge
between 2 bacterial
cells
Plasmid
Conjugation bridge
The donor cell
copies its plasmid
or chromosome and
passes the copy
through the
conjugation bridge
Cells separate
Why are Bacteria important?
– Bacteria are vital to the living world.
• Some are producers that capture energy
by photosynthesis.
• Others are decomposers that break
down the nutrients in dead matter.
• Still other bacteria have human uses.
Human Uses of Bacteria
–foods and beverages
–removal of waste and poisons from
water
–mining minerals from the ground
–synthesis of drugs and chemicals via
genetic engineering
–production of vitamins in human
intestines
Viruses (Cell Pirates)
• Virus: a piece of hereditary material
covered by protein that infects and
reproduces only inside a living
organism
• doesn’t grow, respond, or eat
• some can be made into crystals and
be dormant for years
Virus Structures
RNA
Viral Infection
Lytic Cycle
2.Lysogenic Infection: virus integrates
its DNA into the DNA of host & viral
genetic info replicates along with host
cell’s DNA
- Can remain inactive for long time
Prophage: viral DNA that is embedded
in host’s DNA
-eventually, viral DNA will be activated &
new viruses will be made
Lysogenic Cycle
•
Simply put, both types of viruses
follow the same path in different time
frames:
1. The virus attaches to the cell
2. The virus invades the cell
3. The virus makes copies of its DNA
4. Then the new viruses are released
Section 19-3
Diseases caused by Bacteria and
Viruses
• Pathogens: disease causing agents.
Bacteria produce disease in one of two
ways:
1. Damage the cells and tissues of
the infected organism directly by
breaking down the cells for food.
2. Release toxins (poisons) that travel
throughout the body interfering with
the normal activity of the host.
Bacterial Disease in Humans
Lyme Disease
Bullseye mark around bite
Strep Throat
How do we stop these
types of infections?
Antibiotics – Compounds that block the
growth and reproduction of bacteria; not
effective against viruses.
There are various methods used to control
bacterial growth, including:
• Sterilization – Destroys all bacteria by
subjecting them to great heat for a
period of time. (Autoclave)
• Disinfectants – Chemical solutions that
kill pathogenic bacteria. (household
cleaners)
•Food Storage and Processing
• Refrigerate food
because the
bacteria will take
longer to
multiply.
• Boiling, frying, or
steaming can
sterilize certain
foods.
Viral Disease in Humans
–Viruses can attack and destroy certain
cells in the body, causing symptoms of
the disease.
PREVENTION
Vaccine – Is a preparation of weakened or killed
pathogens. It works by prompting the body to
produce immunity to the disease.
Most vaccines work only if used before an
infection begins.
Viral Diseases in Humans
Chickenpox
• Chicken pox
Smallpox