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Effects of viral infection may be mild or
severe
 The
symptoms of a viral infection vary
depending on the host cell that is destroyed.
 Cell death also triggers immune response
which can cause fevers and inflammation.
 B. Some animal viruses linger for years.
 When virus does not produce symptoms, but
the viral genetic information is still inside
the cell it if called a latent viral infection.
 Examples: herpes simplex 1 and HIV
 Some can cause cancer like HPV and EpsteinBarr
 Antiviral
medications can interfere with
enzymes that are unique to viruses, but few
drugs can kill viruses without killing host
cells.
 The high rate of mutation in viruses make
them unlikely to be curable.
 Vaccines train the immune system to
recognize viruses and combat them before
infection occurs.
 Smallpox and polio have nearly been
eradicated.
 Plant
viruses like the tobacco mosaic virus
cause spots or streaks in plant tissue.
 Plants can fight off viral infections using
posttranscriptional gene splicing. Viral mRNA
is degraded which prevents new viruses from
forming.
 A.
a viroid is an infectious RNA molecule
 Viroids are naked RNA that can infect a cell.
 They cannot encode proteins, but they can
cause serious diseases in crop plants and are
spread by wind, insects, and farm
equipment.
 B. A prion is an infectious protein
 A prion is a “proteinaceous infectious
particle” .
 Prions cause mad cow disease and
Creutzfeldt-Jakob disease.
 16.1
prokaryotes are a biological success
story
 Prokaryotes are single-celled that lacks a
nucleus and membrane bound organelles.
 2 domains- Bacteria and Archaea
 Prokaryotes live everywhere on earth. There
are many species and more are being
discovered.
 Microbiologists learn from cultured cells and
from extracting microbial DNA directly from
the environment.
 A.
Microscopes reveal cell structures
 Internal structures- cell membrane, DNA(a
circular chromosome), ribosomes.
 The nucleoid is the region where the DNA is
located. There is NO nuclear membrane.
 Many also have a plasmid which is a circle of
DNA apart from the chromosome. Plasmids
are used in genetic engineering.
 External structures- Cell wall(most bacteria
and archaea) that is made of peptidoglycan a
polysaccharide.
Coccus- spheres
 Bacillus-rods
 Spirillum- spiral or corkscrew
 Arrangements- clusters(staphylo),
chains(strepto)
 Gram stain reaction distinguishes between two
types of cell walls Gram-positive- thicker cell walls made of
peptidoglycan that stain purple
 Gram-negative- thinner cell walls that stain
pink.
 Gram stain is used for identification purposes.

 Gram-negative
bacteria also have an outer
layer of lipid, polysaccharide and protein.
This causes fever and inflammation. It also
causes the toxic effects of bacteria such as
Salmonella.
 Some prokaryotes also have a slime layer
called a glycocalyx. It is sticky and allows the
bacteria to stick to surfaces, resist drying,
resist immune responses and plays a role in
creating biofilms.
 Pili- short hairlike projections that aid in
attachment.
 Many prokaryotes can move. Taxismovement in response to stimuli.
 Flagella-whiplike projections that aid in
movement.
 Two
genera of gram-positive bacteria
produce endospores(dormant, thick-walled
structures that can survive harsh conditions.
Once conditions improve, endospores
germinate and develop. Ex. Clostridium
botulinium and Bacillus anthacis
 B. Metabolic pathways may be useful in
classification.
 Methods by which organisms acquire carbon
and energy: autotrophs, heterotrophs,
phototrophs, chemotrophs
 Oxygen
requirements- obligate
aerobes(require O2), obligate anaerobes (O2 is
toxic), facultative anaerobes(with or without
O2)
 Prokaryotes
transmit DNA from generation to
generation through vertical gene transfer.
 Binary fission- asexual reproduction – DNA
replicates and then it is distributed to
daughter cells
 Bacterial cells can divide every 20 minutes in
the right conditions.
 New combinations of DNA can only be made
by horizontal gene transfer.
3
types of horizontal gene transfer
 Transformation- bacteria takes in bits of DNA
without contacting another cell.
 Transduction, a virus transfers combined DNA
to a bacterial cell
 Conjugation- DNA is exchanged through a sex
pilus
 Scientists
have identified 23 phyla within
domain Bacteria, but evolutionary
relationships are not clear.
 Major phyla



Proteobacteria-largest group of gram-negative
bacteria. Includes purple sulphur bacteria,
enteric bacteria(E. coli, Salmonella),
vibrios(causes cholera)
Cyanobacteria-autotrophs, some fix nitrogen,
free living or symbiotic
Spirochaetes- sprial shaped, cause lyme disease
and syphilis
 Major



phyla continued:
Phylum firmicutes- gram positive, medically
important, low proportion of G and C in DNA,
cause tetanus, anthrax, strep and staph
Phylum Actinobacteria- filamentous grampositive, high proportion of G and C in DNA, live
in soil, source of antibiotics
Phylum Chlamydiae- grow only in host cells, lack
cell walls, cause chlamydia
As new archaea are discovered we find that
there are some that are do not live in hot, acid,
or salty environments.
 3 main phyla of Archaea




Euryarchaeota-live in stagnant waters and anaerobic
intestinal tracts, generate large quantities of
methane gas, also includes photosynthetic halophiles.
Phylum Crenarchaeota- includes acidophiles and
thermophiles, but also contains a wide variety of soil
and water microorganisms with moderate
temperature requirements
Phylum Korarchaeota- mostly known from genes
extracted from the environment. Some are
thermophiles.
Microbes from vital links in ecosystems
 All species would die without bacteria and
archaea.
 They are essential to carbon cycle, they are
eaten by many organisms
 They are essential to nitrogen fixation, they
make nitrogen useful to organisms.
 B. Bacteria and Archaea live in and on Us
 We are a habitat for microorganisms. They help
us crowd out disease causing bacteria. Most
bacteria living on us are harmless, some cause
disease.

 Bacteria
must enter the body to cause
disease. They can enter by animal bite,
inhaling, sexual activity, or ingesting
contaminated food or water.
 Bacteria cause illness in a number of ways:
damage caused by the bacteria, toxins
produced by the bacteria, enzymes from the
bacteria may damage tissues
 Sometimes bacteria can produce toxins that
remain in poorly refrigerated or undercooked
foods and people get sick from the toxins,
not the bacteria themselves.
 Bacteria can also trigger immune responses.
 Many
foods are produced by bacterial
metabolism. Ex. Cheese, yogurt, vinegar
 Many microbes have industrial applications:
ex. Vitamins, ethanol and acetone
 Transgenic bacteria produce insulin and
blood clotting factors
 Bacteria are used in wastewater and sewage
treatment. They also remediate pollutants.