Download Bacteria & Viruses

Bacteria & Viruses
By the end of this class you should understand:
• How life may have arisen from nonliving
materials
• Modern classifications of bacteria and familiar
species we encounter every day
• The life cycle of parasitic protists
• How viruses work and whether they are alive
• How to protect yourself from bacteria and
viruses
Early Life on Earth
• Life first appeared around 3.8
billion years ago, soon after
liquid water formed
– Not recognizable as modern
life
• Fulfilled the basics of life
– Reproduced
– Took in energy
– Probably didn’t maintain
homeostasis very well yet
Nonliving Synthesis
• Life is formed from large assemblies
of macromolecules
– How could these have been
assembled without life?
• There are a number of hypotheses
on how these molecules could have
been assembled
– Clay deposits that preferentially
collect charged particles and then
dried up
– Hydrothermal vents at the ocean
floor naturally produce carbon
molecules
Protocells
• One way or another, these
molecules eventually formed into
protocells
– Protocells have been studied as a likely
mechanism for a precursor to life
• Essentially, fatty acids collect into a
simple membrane, and inside,
enzymes made of RNA called
ribozymes convert other molecules
into RNA
– Cell grows as more RNA is absorbed
and splits naturally
Evidence for Protocells
• A lot of evidence exists that
this mechanism is possible,
but that’s not the same
thing as evidence that it
actually happened
• The key evidence is protein
synthesis
– Common to all life
– Uses RNA-based process
(ribosomes and tRNA)
Prokaryotes Revisited
• Modern bacteria are nothing
like early bacteria
• Through natural selection, only
the hardiest and fastestreproducing bacteria were
represented in the next
generation
– Bacteria can ideally reproduce in
20 minutes
– One bacterium in a soup of
nutrients can make a colony of
100 million bacteria in 12 hours
Three Modern Domains of Life

Archaea



Eubacteria



Bacteria that resemble early life
Live in unusual environments
What we think of as bacteria
All pathogens are eubacteria
Eukarya

All eukaryotes including humans
Archaea


Oldest and least changed bacteria
Many live in hostile environments






Extremely acidic
Deep ocean vents
Boiling hot springs (extreme thermophiles)
Salt marshes (extreme halophiles)
Oil wells
Others live in more “normal” environments
Eubacteria


Most bacteria that we are familiar
with
Many are harmless or even helpful


Bacteria that live on our skin and in
our gut are called normal flora and
they crowd out more dangerous
bacteria
Some are dangerous to our health


Usually eat our tissues for nutrients
Some release dangerous toxins
instead
Classifications of Eubacteria

Gram staining

Gram positive: turn purple in a Gram stain
•

Has a cell membrane and a crunchy cell wall
Gram negative: stay pink in a Gram stain
•
Has two cell membranes with a wall between
Another Classification

Aerobic
– Aerobic bacteria can survive in air
– Many bacteria on the skin
– Mitochondria are related to early aerobic
bacteria

Anaerobic bacteria
– Die when exposed to air
– Lack catalase and peroxidase enzymes
– Many bacteria in your gut and that spoil food
How do anaerobes get around?




Solution: spores!
Some bacteria create
spores in harsh
conditions
These spores can
survive almost
anything
Turn back into bacteria
when the conditions
have improved
Bacteria shapes





Coccus – sphere
Bacillus – rod
Spirillum –
spiral
Many other
weirder shapes
also exist
Often in the
bacteria name
Staphylococcus



Gram positive
Common on human skin,
usually harmless
Some are harmful



Infections
Food poisoning
Responsible for “Staph
infection”
Streptococcus



Gram positive
Many also found on human
skin
Dangerous strains responsible
for “strep throat”


Even more dangerous types
cause Scarlet fever
Most dangerous is “flesheating” bacteria

Pictures not provided for the faint
of stomach
Escherichia coli





“E. coli”
Gram negative
Common in human digestive tract
Helpful for metabolism
Some virulent strains exist


“E. coli” outbreaks are really “Rare
and dangerous strain of mutated E.
coli outbreak”
Often not the bacteria that is
harmful but the toxins it produces
Salmonella




Gram negative
Commonly found in humans
and farm animals
Can cause food poisoning in
undercooked poultry products
Other species cause typhoid
fever


Infect human cells using a
capsule
Potentially lethal
Antibiotics

Antibiotics are chemicals that
selectively kill bacteria and not
eukaryotic cells




Ineffective against human, yeast, and
protozoa
Effective against certain types of
bacteria only
Penicillin was the first antibiotic that
killed all Gram-positive bacteria
Ampicillin and Streptomycin kill all
bacteria
Antibiotic resistance

Bacteria constantly mutate and
develop new genes


Bacteria also pass genes to each
other on plasmids, small rings of
DNA
As a result, bacteria may
develop a resistance to an
antibiotic, so taking antibiotics
regularly is generally
inadvisable

Additionally, antibiotics kill the
normal flora of your intestines
and possibly your skin
Better the devil you know...


MRSA (methicillinresistant Staph aureus) is
very dangerous
Can have many
resistance plasmids


Becoming increasingly
common in hospitals
Best defense is a healthy
immune system and
normal flora
This is a real problem…
Protists
• Protists are eukaryotic single-celled organisms
– Amoebas, paramecium, etc.
– Many probably resemble early eukaryotes
• I will not be covering most of the protists since
there are approximately a hojillion of them,
but I will cover Plasmodium, the protist that
causes malaria
– Because I’m friendly like that!
– Most protists are NOT infectious
Malaria Life Cycle
Virus


A virus is a nonliving infectious particle that
uses genetic information to reproduce
All viruses reproduce by injecting their genetic
molecules into a host cell


The genetic molecules (DNA or RNA) force the cell
to make more viruses
Viruses have no metabolism of their own and do
not maintain homeostasis or reproduce
independently
Parts of a Virus

All viruses have:




Protein coat
Spikes that
target host cell
Genetic material
Some viruses
have a
membrane called
an envelope
What about these weirdos?




This is a bacteriophage
Virus that infects bacteria
Useful in scientific research
Keeps its DNA in the capsule,
injects it through the tube
into the bacteria

Bacteria have enzymes that try
to chop up DNA that doesn’t
belong, so it’s an ongoing arms
race!
What does the genetic info do?



Sample: HIV in
human cell
Essentially the
DNA or RNA
causes the cell to
make more viral
proteins
The viruses are
exocytosed or bud
off with envelope
until the cell dies
Host specificity


The virus spikes can only latch onto certain
receptors
This keeps viruses from freely moving
between different species of animals


Crossover occurs due to mutation, e.g. “bird flu”
Viruses can only infect certain cells in the host



HIV only infects Helper T cells
Rhinovirus infects epithelial cells
Some viruses (e.g. herpes) infect nerve cells
•
These are generally incurable
Antibiotics NOT for Viruses
• Do NOT take antibiotics for viruses
– Not only will it do nothing, it exposes you to potential
bacterial infections to go with your viral infection!
• Vaccines are available for some viruses
– A vaccine is a piece of a bacterium or virus that your
immune system “learns” to kill
– Pre-training your immune system so you don’t get the
same disease again
• Many viruses and some bacteria mutate too
quickly to have effective vaccines made!
Protip:
• VACCINES DO NOT CAUSE AUTISM
• There was a time when vaccines were packaged with
an antiseptic called thimerosal, which is a mercurycontaining compound
– They are no longer packaged as such
• The original study linking vaccines and autism was
discredited, and many scientists have repeated the
experiment but found no statistically significant
difference
• Autism is a developmental disorder and more
prevalent in males, it cannot be caused by an injection
at six months of age
See you in lab!