Viruses and Prokaryotes
What is a Virus?
• A virus is a noncellular particle made up
of genetic material and protein that can
invade living cells
• Structure
– Core of nucleic acid surrounded by a protein
coat called a capsid
– Capsid can be DNA or RNA, but not both
– Core can be several to several hundred
genes
SO HOW BIG ARE
VIRUSES???
• Viruses are REALLY
small.
• They are much smaller
than bacteria.
• They can only be seen
with an electron
microscope.
Bacteriophage
• Bacteriophages are viruses that infect
bacteria
• Bacteriophage
– Head – capsid and DNA
– Tail – with fibers to attach to bacteria
T group
• Most commonly studied are T group – T1,
T2, T3, T4 etc...
• T4 has a DNA core within a protein coat,
and tail with tail fibers to attach to bacteria.
Viral shapes
• Variety of shapes
– Rod
– Tadpole
– Many sided, helical or cubelike
VIRUS SHAPES
• Round
• Rod-shaped
• Many sided
(icosohedral)
SHAPES MAY DIFFER BUT…
• All viruses have
• 1. Chromosome-like part that carries hereditary information – The Core
• 2. Protein coat: Protects hereditary information and provides the shape! The
Capsid
Tobacco Mosaic
Virus
T4 Bacteriophage
Head
DNA
Influenza
Virus
RNA
Capsid
proteins
Capsid
RNA
Tail
sheath
Tail
fiber
Surface
proteins
Membrane
envelope
ROUND VIRUSES
• Herpes virus
–There are
two types:
• Genital
• oral
ROD-SHAPED
• Tobacco
mosaic
virus
MANY SIDED
• bacteriophage
E coli bacteria
Is this why viruses infect us?
• YES!
• Viruses need
living
organisms in
order to
reproduce and
form more
viruses!
Injecting DNA virus
Virus Size
• Size – 20 to 400 nanometers (one
nanometer is one billionth of a meter)
• Specificity – usually infect specific
organisms
– Cannot infect animals if it infects plants
– Some can infect wider variety
– Rabies – all mammals, some birds
VIRUSES ARE SPECIFIC IN
THE CELLS THEY INFECT
Tobacco mosaic virus: only tobacco
plants…not wheat or corn
Rabies: only nervous system cells of mammals
Common cold: infects cells on airway passage to
lungs
Lytic Infection
•
Cause cells to lyse or burst
1. Infection – chance contact virus with right kind of bacterium. Virus
attaches to bacterium and injects its DNA. Most times, complete
virus particle does not enter.
2. Growth – Bacterium can’t tell difference between bacterial and viral
DNA. RNA polymerase causes mRNA to be made from cell for
virus. Viral DNA takes over and produces more DNA and viral
proteins.
3. Replication – Virus uses bacterial material to make thousands of
copies of the protein coat and DNA. Cell becomes filled with virus
particles. (All three stages can happen with E. coli within 25
minutes!)
4. DNA serves as central point for virus particles to be assembled.
Cells fill with virus and lyse (burst). New viruses can now infect new
cells.
SO HOW DO VIRUSES CAUSE
DISEASE?
Section 19-3
Bacteriophage
protein coat
Bacteriophage DNA
Bacterial
chromosome
Bacteriophage attaches to
bacterium’s cell wall
Bacteriophage enzyme lyses the
bacterium’s cell wall, releasing
new bacteriophage particles that
can attack other cells.
Lytic Cycle
Bacteriophage injects DNA
into bacterium
Bacteriophage proteins and
nucleic acids assemble into
complete bacteriophage
particles
Bacteriophage takes over
bacterium’s metabolism, causing
synthesis of new bacteriophage
proteins and nucleic acids
Bacteriophage
Bacteriophage DNA
Bacteriophage protein
Retroviruses
• RNA viruses
• When they infect a cell, they produce DNA
copies of their RNA genes.
• Retroviruses have their genetic information
copied backwards. RNA  DNA
• One retrovirus is HIV. Others cause cancer in
animals and humans.
• The theory is that viruses were not the first living
things. They are dependent on living things to
survive.
EUBACTERIA AND
ARCHAEBACTERIA:
The two bacterial
kingdoms
Bacteria on a pin head
Eubacteria
• “True” bacteria
• largest Kindgom of prokaryotes
• generally surrounded by cell wall composed of
complex carbohydrates
• have a cell membrane (some have 2 cell
membranes)
• Some have flagella for movement
• Found everywhere
• Some produce disease
• Some photosynthetic
• some very useful – cheese is just one example
PROKARYOTIC CELLS
• Prokaryote – what does that mean?
Classification of Prokaryotes
• All prokaryotes were in kingdom Monera.
• Now – 2 kingdoms
– Eubacteria and archaebacteria
Archaebacteria
• Archaebacteria includes organisms that
live in very harsh environments
• Methanogens – live in oxygen free
environments – mud, digestive tracts of
animals
• Extremely salty environments
• Hot springs
Identifying Bacteria
• Cell Shape
– Rod – bacilli
– Sphere – cocci
– Spiral – spirilla
Bacterial Shapes
Round
Rod
Spiral
Arrangement
• 2 cocci – diplococci
• long chains – streptococci
• clumps, clusters – staphylococci
Cell Wall
• Chemical nature – Gram staining
• Hans Christian Gram
• 2 dyes – crystal violet (purple) and safranine
(red)
– bacteria either take one or the other
– If only one thick layer of carbohydrate and protein
molecules outside the cell membrane – picked up
crystal violet – appeared purple – GRAM POSITIVE
– If cell had 2nd, outer layer of lipid and carbohydrate –
picked up safranine – appeared red GRAM
NEGATIVE
Bacterial movement
• propelled by flagella
• lash, snake, or spiral forward
• no movement
Bacterial Respiration
• Obligate aerobes – require oxygen
• Obligate anaerobes – must live in
absence of oxygen
– example is Clostridium botulinum
• Facultative anaerobes – can live with or
without oxygen
Reproduction
• Some can reproduce every 20 minutes
• Held in check by food and production of wastes
Types:
• Binary Fission
• Replication of DNA and division in half
• Asexual
• Conjugation
• Sexual – involves the exchange of genetic material
• Long bridge of protein forms between the cells
• Donor genetic information transferred to recipient
through bridge
• Recipient cell has different genes at the end than it did
to begin with
Importance of Bacteria
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Used in production of products we use every day
Yogurt
Cheese
Buttermilk
Sour cream
Pickles
Sauerkraut
Vinegar
Wine
Industry
digest petroleum
remove wastes and poisons from water
synthesizing drugs – through genetic engineering
Symbiotic Relationships
(mutuallism)
• E. coli in humans – help us digest food –
make vitamins we can’t, we give them a
home, food, and transportation
• Bacteria in the intestines of cattle allow
them to break down cellulose (in grass
and hay)
Bacteria in the Environment
• Bacteria are like the stage hands that
allow the show to go on without being
seen (or always given the credit)
• Bacteria recycle and decompose dead
material
• Saprophytes – organisms that use the
complex molecules of a once living
organism as their food source
Sewage decomposition
• Sewage treatment – bacteria is added
directly to the raw sewage
• How does a septic tank work?
Nitrogen Fixation
• All organisms are TOTALLY dependent on
monerans for Nitrogen
• All Plants need nitrogen to make amino acids (NH2)
• Because animals eat plants, they get their
proteins from plants
• What percentage of the air is Nitrogen?
• Plants, and most other organisms cannot use
this directly
• Need Nitrogen to be “FIXED” chemically as
ammonia
Nitrogen Fixation
• Scientists can make synthetic nitrogen containing
fertilizers by mixing Nitrogen and Hydrogen gases,
heating to 500 degrees C and compressing it to 300 X
normal atmospheric pressure – dangerous, expensive,
time consuming
• Many cyanobacteria can take nitrogen from the air and
convert it to a useable form – this is called Nitrogen
Fixation
• Bacteria are the only organisms that can do this.
• Some plants have a symbiotic relationship with nitrogen
fixing bacteria
• soybean – Rhizobium grows in nodules around roots
Diseases caused by Viruses and Monerans
• only a small number of viruses and
bacteria can cause disease
• Pathogens – organisms that cause
disease
• All viruses infect living cells
• Disease occurs when infection causes
damage to the cells
Viruses and Disease
• Examples are:
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Small Pox
Polio
Measles
AIDS
Mumps
Influenza
Yellow Fever
Rabies
Common Cold
Ebola etc…
Vaccine
• The body’s own defenses must be used
• Vaccine – dead or weakened viruses that
stimulate the bodies defense system
• Symptoms can be treated sometimes, but
once someone is infected by a virus, there
is not much science can do
Bacteria and Disease
• Bacterial diseases include:
– Diptheria
– TB
– Typhoid
– Tetnus
– Hansen disease
– syphilis
– cholera
– bubonic plague
– Flesh Eating Bacteria
2 ways bacteria cause disease
1. Damage cells and tissues of infected
organisms directly by breaking down cells
2. Releasing toxins (poisons)
• Many bacteria can live without a host organism
(on a petri dish)
• Rickettsiae cannot live outside a host cell. They
have leaky cell walls
• Rickettsiae cause Rocky Mountain Spotted
Fever, typhus, and Legionnaire’s disease
• Measures to fight bacterial infection
include:
– Antibiotics – drugs and natural compounds
that attack and destroy bacteria in the body
– NOT Effective against viruses