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Viruses
Viruses
What are they?
How do they work?
Where do they come from?
And… What good are they?
Viruses: Making a Living by Hijacking Cells
Not living organisms; lack some attributes of life.
Are infectious particles, can’t replicate
independently.
Not cells and don’t carry out metabolism
Made of RNA or DNA usually enclosed in protein
coat (viroids lack protein coat).
Protein coat (capsid) takes
many shapes.
DNA or RNA is always
within the capsid
Some viruses have an
envelope to cover them!
Envelope – came from host’s
cell membrane when virus
budded out of host
They have no envelope
Some VIRUSES have no envelope – they’re naked! HERE IS A virus
THAT INFECTS BACTERIA – It is called a bacteriophage.
How Big are viruses?
Polio virus = 20 nanometers
20nm
1 nm – 0ne billionth of a meter!
3000 polio viruses fit across the diameter of a
period at the end of a sentence in your book.
Viruses can’t reproduce
on their own
• They must invade a cell.
• Once inside a cell, they cause the
cell to make more viruses instead
of their usual proteins.
• They are intracellular obligate
parasites – they can’t do anything
on their own.
The lytic cycle demonstrates the steps that a virus
takes in order to take over a cell.
The steps are:
1. Attachment
11
2. Injection
5
3. Replication
4. Assembly
5. lysis
2
3
4
Sometimes the virus doesn’t kill the
cell right away and it becomes part
of the cell’s genes.
If this happens, the virus DNA
becomes a prophage and can become
activated at any time (like a time
bomb).
In the meantime, the prophage is
passed on to all the offspring of
that cell …. Maybe for many
generations.
.
When were viruses discovered?
Viruses have apparently always been around.
However, it wasn’t until 1897 that a Dutch
scientist named Beijerinck called an invisible
agent that was smaller than bacteria a virus
(Latin for poison). He was studying tobacco
leaves that had been infected with what we
now know as tobacco mosaic virus.
Classification of Viruses
By Shape
by Host type
by function
Animal viruses
Retroviruses
attack a certain
way.
DNA viruses attack
another way.
Plant viruses
Bacteria viruses
Retroviruses
Contain RNA
When infecting a cell, these viruses
have to transcribe the RNA to DNA
before the viral code can be read.
This requires an enzyme, reverse
transcriptase, to Change RNA to DNA
then the viral code can be added to the
cell’s DNA.
Once part of the cell’s Dna, the viral
code can cause the cell to make more
viruses.
HIV IS A RETROVIRUS
Gp120 & gp41
envelope
HIV LIFE CYCLE
1
2
hiv
3
4
gp41
5
6
7
HOW HIV GETS INTO A CELL
HIV infecting a T cell
hiV IN A CELL AND
BUDDING OUT OF A
CELL
Ways to get HIV
At birth from mother
Dirty needles
Unprotected sex
Treatment includes trying to
enhance body defenses using stem
cells
TREATMENT INCLUDES INHIBITORS OF
ENZYMES:
1. Reverse transcriptase inhibitor
This enzyme allows viral RNA to code for DNA
2. Protease inhibitor
This enzyme allows viral proteins to be cut and fit into the
final virus
3. Integrase inhibitor
This enzyme allows the virus DNA to join the cell’s DNA in the
nucleus
Effects of treatment are evident when
comparing infections suffered by AIDS
patients in 1993 with those in 1997
Drug-resistant HIV
T-cell count as disease progresses
WAYS TO AVOID GETTING
hiv IN THE FIRST PLACE
• ABSTINENCE.
• SAFE SEX – ALTHOUGH NO METHOD IS
100 % SAFE.
• DON’T SHARE NEEDLES OR ANYTHING
THAT CAN MIX BLOOD.
Viruses infect many organisms, including bacteria, plants, and
animals; cause much agricultural loss, mild to deadly human
diseases (cold, flu, chickenpox, herpes, rabies, AIDS, some
types of cancer).
polio
ebola
flu
smallpox
Aren’t you glad
we don’t get
smallpox
anymore?
Smallpox has
been eliminated
from the world
as a result of
immunizations
Vertebrates defend against viruses through
antibody-based immunity or cellular immunity.
1.
Immune system produces specific proteins (antibodies) that recognize and bind viral
particles, thereby blocking their replication.
2.
Immune cells called T cells recognize and destroy cells harboring viruses (cellular
immunity).
After first infection, body retains clones of antibody or T cells directed against
that viral strain:
3.
Rapid defense is mounted upon second infection.
This is what happened when you recovered from chicken pox.
This immune memory is the basis of vaccination;
vaccine consists of killed or nonfunctional
viruses, triggers immune response in body
without disease symptoms upon subsequent
infection with active virus.
Dr. Edward Jenner produced the
first vaccine that was used widely.
He injected cowpox pus into a boy;
the boy got cowpox and recovered.
Jenner then injected the boy with
smallpox pus and waited…..the boy
did not get smallpox.
Nonviral infectious agents
• Prions
– PIECE OF PROTEIN
– CAUSE OF MAD-COW
DISEASE
– CAN INFECT ANIMALS –
INCLUDING HUMANS
• vIROIDS
– Single strand of
RNA
– Causes plant
diseases
Human diseases caused by viruses
•
•
•
•
•
•
•
•
Common cold
Influenza (flu)
Chickenpox
Polio
HIV
Some pneumonia
Some meningitis
herpes
Domain Bacteria:
Masters of Every Environment
Bacteria exist in staggering numbers in wide
range of habitats.
1. Microflora of human gut includes 600 species
of bacteria in mouth alone; quarter of feces
by weight consists of bacteria.
YUCH!
Gut bacteria
A. Bacteria exist in staggering numbers in wide range of
habitats.
2. Nitrogen-fixing bacteria have symbiotic relationship
with some plants: convert molecular nitrogen into
forms usable by plant; nitrogen needed by animals comes
ultimately from plants.
3. Bacteria play an important role as decomposers (as in
city sewage plants)
Bacteria varied in shapes:
1. Cocci--spherical
2. Bacilli—rod-shaped
3. Spirochetes—spiral-shaped
Bacteria enormously diverse: 4,000 to 5,000
species found living in 1 gm of forest soil.
Some bacteria names have prefixes
that describe their structure
• Diplo = bacteria in pairs
– Ex – diplococcus or diplobacillus
This diplococcus
causes gonorrhea
Strepto = means chain of cells
streptococcus or streptobacillus
Staphylo = means cluster
Ex – staphylococcus – a major cause of infection
in hospitals
Characteristics of bacteria:
1. lack cell nucleus, as do all
prokaryotes (eukaryotes have
nucleus).
2. Have almost no other cell
organelles, no cytoskeleton.
3. DNA present as single chromosome;
haploid organisms.
Bacteria cell - Prokaryotic
plasmid
Reproduction is asexual, by simple
splitting (binary fission); daughter
cells genetic clone of parent cell.
Are single-celled; may form colonies.
(EACH DOT ON THE PLATE IS A COLONY MADE UP OF MILLIONS OF BACTERIA)
We combat disease-causing bacteria with
antibiotics.
1. Most antibiotics are from fungi, which have
waged war of survival with bacteria.
2. Antibiotics must exploit differences in cell
biology of bacteria and humans to keep from
harming patient (e.g., penicillin destroys
bacterial cell walls, but has no effect on
animal cells).
Antibiotics, when placed on a paper disc,
inhibit growth of bacteria in Petri dishes….
The larger the zone of inhibition, the more
effective the antibiotic is.
Least effective
most effective
Mode of nutrition
Autotrophs
Photoautotrophy—Use light energy and
carbon dioxide to create energy-rich
carbon compounds, as plants do too.
Chemoautotrophy—Use inorganic compounds
(hydrogen sulfide, ferrous iron) to fix
carbon from carbon dioxide.
Most Monerans are
Heterotrophs
Escherichia coli
spirillum
anthrax
Domain Archaea - Newly recognized as
ancient group of prokaryotes.
Divergent from all other life-forms;
majority of genes (from Methanococcus)
unique to group, not previously known
to science.
Stromatolites –
Rock formations
made by some of
these bacteria
Some live in extreme environments (extremophiles):
High or low temperatures, high pressure, high
salt, extreme pH.
Thermophiles: live in hot water
Halophiles: live with high salt
Great Salt Lake
Endospore production – preserves the cell
during hard times– not a form of
reproduction
• Steps in formation of an endospore
Endospore
Bacteria that are
harmful to humans and
that form endospores:
Clostridium tetani –
causes tetanus
Clostridium botulinum –
causes deadly food
poisoning
Cell Wall Composition – gram
positive or gram negative
• Gram positive Gram negative
• Stains blue
stains pink
Respiration – process of
getting energy from food
Aerobic
» Need oxygen
» Can’t live without oxygen = obligate aerobes
» EX – TUBERCULOSIS BACTERIUM
Tb lung
» Prefers to live with oxygen = facultative
aerobes
• Anaerobic –
– don’t need oxYgen
– SOME CAN’T SURVIVE WITH OXYGEN –
THESE ARE OBLIGATE ANAEROBES
EX – TETANUS
This baby probably got tetanus from
honey – don’t give honey to a baby!
SOME CAN LIVE WITH OXYGEN BUT PREFER TO
LIVE WITHOUT IT – fACULTATIVE
ANAEROBES
E. coli
How Important are
bacteria to the world?
• Decomposition – most important
function for living things. What
happens to all the dead bodies?
• Here is a bacterium
of decay
Food web
Nitrogen cycle
Cow Digestion
Tooth Decay
Yuch!
Don’t forget to brush and floss your teeth!
Foods from bacteria
cheese
yogurt
sauerkraut
Diseases caused by bacteria
Anthrax – a natural pathogen that can be used for
bioterrorism
Lyme disease – causes illness
and can lead to arthritis
plague
gonorrhea
Strep throat
Food poisoning
Salmonella food poisoning
– from eggs, chicken,
mayonnaise
Botulism –
from
improperly
canned foods
Here is a white blood cell
attacking a bacillus
Medical uses of bacteria
• Genetic engineering to produce medical
products –
– Insulin
– Human growth hormone
Gene for human insulin or hgh
Now all cells will have the gene and
will make the product
Uses of bacteria other
than food production
• Bioremediation – using
microorganisms to rid environment
of harmful substances
– Ex – oil spill site
– Hazardous waste site
– Sewage treatment
Medical uses of bacteria
• Genetic engineering to produce medical
products –
– Insulin
– Human growth hormone
Gene for human insulin or hgh
Now all cells will have the gene and
will make the product
What conditions do bacteria need
for the best growth?
1. Food source (your soup is good)
2. Proper temperature - human
pathogens (disease causers) live best
at 98.6 F.
3. Moisture
4. Oxygen (aerobes) or not (anaerobes)
Change any of these and the growth of
bacteria can be slowed down or
stopped.
We compete with bacteria for our
food – they eat the same stuff we
do…. How do we preserve our
food?
Drying (prunes)
salting
refrigeration
freezing
pickling
That’s all folks!