Viruses and Bacteria
Chapter 18
What is a virus?

Considered non-living particles by most
biologists because they:
– Do not carry out cellular respiration
– Do not grow and develop
– Cannot replicate on their own

Viruses are named after:
– The disease they cause (poliovirus)
– The organ they infect (adenovirus)
Viral Structure

Genetic Material in
the form of:
– DNA
– RNA

Capsid: outer protein
coat
– 4 common shapes
 Polyhedral
 Helical
 Enveloped
 Bacteriophage or
phage
Polyhedral Viruses
Herpes virus
 Adenovirus
 Polio virus

Helical Viruses

Tobacco
Mosaic Virus
Enveloped Viruses

Contain an envelope
made of
– Lipids
– Carbohydrates
– Proteins

Examples
– Influenza Virus
– HIV
Bacteriophages
“phage”
 Is a virus that attacks
bacteria

Viruses are Specific
Each virus is
specialized
 Most viruses
are speciesspecific
 Many viruses
are also cellspecific

Viral Replication Cycles

Lytic Cycle
– Kills the host cell

Lysogenic Cycle
– Similar to lytic cycle but does not immediately
kill host cell
– Viral genetic material recombines with host
cell’s DNA
– Provirus: Viral DNA that is integrated into host
cell’s chromosome
 Examples: HSV I & II, hepatitis B, and chicken pox
Lytic Cycle






A virus attaches to a host cell.
Virus releases its genetic material
into the host cell.
The injected genetic material
recruits the host cell's enzymes.
The enzymes make parts for more
new viruses.
The new parts assemble into new
viruses.
The new particles lyse (burst) the
host cell and exit.
Lysogenic Cycle

Retroviruses
Type of RNA
virus that reverse
transcribes itself
into DNA
 The newly
transcribed DNA
inserts into host’s
DNA
 Ex: HIV

Prokaryotes
Unicellular organisms
without membranebound organelles
 2 Kingdoms

– Archaebacteria
– Eubacteria
Archaebacteria
Live in harsh environments
 3 types

– Methane-producers




“Methanogens”
Marshes
Lake sediments
Animal digestive tracts
– Salt-dwellers
 “Halophiles”
 Dead Sea
– Heat/Acid-dwellers
 “Thermoacidophiles”
 Deep ocean vents
Eubacteria: The Heterotrophs
Bacteria that obtain their
nutrients from elsewhere
 Some are parasites

– Feed off of living
organisms

Some are saprophytes
– Feed on dead organisms
– Feed on organic wastes
(recyclers)
Eubacteria: Photosynthetic
Autotrophs
Bacteria that convert
solar energy into food
 Cyanobacteria or
blue-green algae
 Found in aquatic
environments
 Composed of chains
of independent cells

Eubacteria: Chemosythetic
Autotrophs
Break down and release
energy from inorganic
compounds such as H2S
 Important in converting
atmospheric nitrogen
into usable forms plants
need

– Nitrogen Fixation
Structure
Identifying Bacteria: Gram Stain

Gram staining reflects
differences in cell wall
composition
– Gram-positive bacteria
stain blue/violet
– Gram-negative bacteria
stain pink
Identifying Bacteria: Shapes
Bacterial Reproduction
Asexually by binary
fission
 Very rapid at optimal
conditions

– can double every 20
minutes
Bacterial Reproduction

Sexually by conjugation
Common Bacterial Diseases
Disease
Agent
Symptoms
Treatment
Strep Throat
Streptococcus
pyogenes
sore throat, fever
antibiotic
Tetanus
C. tetani
stiff jaw, muscle spasm,
paralysis
antibiotic, clean
wound
Tuberculosis
M. tuberculosis chronic cough, chest pain, antibiotic
blood in sputum
Dental Caries
S. mutans
toothache
remove decay
Botulism
C. botulinum
blurred vision, paralysis,
slurred speach
antitoxins
Cholera
Vibrio cholera
diarrhea, vomiting
re-hydration,
antibiotic
Traveler's Diarrhea Escherichia coli stomach cramps, diarrhea
re-hydration,
antibiotic
Beneficial Bacteria

Nitrogen Fixation
N2
→
NO2- + NO3-
Converts Nitrogen into a
usable form for plants

Food
–
–
–
–
–
Yogurt
Cheese
Pickles
Sour cream
Sauerkraut