Unit 3 – Chapter 19
 Latin
= “Poison”
 A tiny disease-causing agent consisting of
a core of nucleic acid, usually encased in
protein.
 Not cellular
 Cannot move about on own
 Cannot carry on metabolic activities
independently
 Pathogen – a disease causing agent
 Consist
of a core of nucleic acid
• Contain either DNA or RNA (not both)
 Surrounded
by a protein coat
• Lack Ribosomes and enzymes necessary for
protein production
 Classified
according to common
characteristics
• Type of nucleic acid
• Presence or absence of a protein coat
 Does
not use Linnaean system
 Escaped
Gene Hypothesis
• Viruses were originally fragments of DNA or RNA
that “escaped” from cellular organisms
• Some viruses may trace their origins to animal
cells, plant cells, or bacterial cells
• May explain why each virus usually infect only
certain ‘related’ species
 Viruses
that attack/kill
bacteria
 AKA “Bacteria Eaters” or
“phages”
 Complex virus
 Used to be used in place
of antibiotics and sulfa
drugs
 They are making a
comeback because of
bacterial resistance to
antibiotics
Used to
attach to
bacteria
 Lytic
Cycle vs. Lysogenic Cycle
The life cycle of a virus that kills the host cell by lysing
(destroying) it
 Forces host cell to replicate viral particles by using its
metabolic machinery
1.
The virus attaches to receptors on the host cell wall
2. Nucleic acid of virus moves through plasma
membrane and into the cytoplasm of the host cell
3. The protein coat remains on the outside exterior of
the host cell
4. The virus uses the cell’s metabolic machinery to
make new bacteriophage viruses
5.
Bacterial cell lyses and releases many phages to
infect other cells
6. Results in the death of the host cell

 The
life cycle of a virus that kills the host
cell by lysing (destroying) it
 Forces host cell to replicate viral particles
by using its metabolic machinery
1.
2.
3.
4.
5.
6.
The virus attaches to receptors
on the host cell wall
Nucleic acid of virus moves
through plasma membrane and
into the cytoplasm of the host
cell
The protein coat remains on the
outside exterior of the host cell
The virus uses the cell’s
metabolic machinery to make
new bacteriophage viruses
Bacterial cell lyses and releases
many phages to infect other
cells
Results in the death of the host
cell
Fig. 19-2, p. 367
 Describe
 What
the Lytic Cycle.
organisms does it occur in?
 Integrate
their DNA into the host bacteria
cells’ DNA
 Does not destroy its host
 Prophage – when viral nucleic acid is
integrated with bacterial DNA
 When bacterial DNA replicates, viral
prophage replicates
 Bacterial cells carrying prophages are called
“lysogenic cells”
 Can spontaneously turn to lytic
Lysogenic Cycle
Fig. 19-3, p. 368
NO



Not cellular
A cell is “the basic unit of
life”
By itself, a virus can do
nothing
YES


• It cannot metabolize
• It cannot reproduce

Does not have the metabolic
machinery nor cellular
structures to do so

Once in the presence of a
living cell a virus behaves as
if it were alive
It reproduces by taking over
the metabolic machinery of
the host cell
Uses the cell’s enzymes,
ribosomes, and other
components
 Are
viruses alive?
 Viroid:
• Small & Circular in shape
• Infectious molecule of RNA
• Causes many plant diseases
 Prion
• An infectious agent
• Composed only of protein
 Cellular
organisms
 2 Domains– Bacteria & Archea
 3 main shapes
• Cocci – Spherical
 Groups of 2 – Diplococci
 Long Chains – Streptococci
 Irregular grape-like clumps – staphylococci
• Bacilli – Rod Shaped
• Spirilla – Helix Shaped
Fig. 19-5a, p. 370
Fig. 19-5b, p. 370
Fig. 19-5c, p. 370
 Prokaryotic
cell structure is simpler than
eukaryotic cell structure
 Lack membrane-bound organelles
•
•
•
•
•
No nuclei
No mitochondria
No chloroplasts
No endoplasmic reticulum
No Golgi apparatus
 Mostly Unicellular
 Small is size (typically
1/1000 the size of a
Eukaryotic cell)
 Usually have a cell wall
Fig. 19-6, p. 371
 Prokaryotes
are heterotrophs
• Hetero = “other” Tropho = “nourishment”
• Must obtain organic molecules from other
organism
 Most are decomposers
 They get their nourishment from dead organic matter
 Or they live in or on other organisms
 Commensals – neither help nor harm their hosts
 Parasites – live at the expense of their host and can cause
disease
 Mutualistic – both organisms benefit from the association
 What
is the difference between parasitic,
commensal, and mutualistic prokaryotes?
 Some
prokaryotes are Autotrophs
 “Auto” = self
“tropho” = nourishment
 Manufacture their own organic molecules
from carbon dioxide
 Photosynthetic prokaryotes –
• Obtain energy from light
 Chemiosynthetic
prokaryotes -
• Obtain energy from chemical reactions
 Most
Prokaryotes are Aerobes
• They require atmospheric oxygen for cellular
respiration
 Some
are Faculative Anaerobes
• They use oxygen for cellular respiration if
available, but will respire anaerobically when
oxygen is absent
 Some
are Obligate Anaerobes
• Carry on cellular respiration only in the absence of
oxygen
 Binary
Fission
• One cell divides into two similar cells
 Conjugation
• Two cells of different physiological mating types
come together, and genetic material is transferred
through pilli from one cell (donor) to the other
(recipient)
Donor
cell
Conjugation
pilus
Recipient
cell
Fig. 19-10, p. 373
 Biofilms
are microbial communities that
consist of many species of prokaryotes
• In watery environments, unicellular organisms
secrete a slimy, glue-like substance rich in
polysaccharides
 They embed themselves in it.
 Ex. Dental Plaque
ARCHAEA


Absence of peptidoglycan in
cell wall
Most live in harsh
environments
BACTERIA




Present almost universally
Abundant in air, soil, water
Abundant in bodies of
organisms
FEW PLACES ON EARTH
ARE COMPLETELY
DEVOID OF BACTERIA
 3 Main Types
• Methanogens (methane producers)
 Obligated anaerobes that produce methane gas from simple
carbon compounds
 Live in sewage and swamp sediments
 Common in digestive tracts of humans and other animals
• Halophiles
 Live in very salty environments
 Use aerobic respiration to make ATP
 Carry out a form of photosynthesis – using purple pigment
• Thermophiles
 Grow in hot and acidic environments
 Found in hot springs and volcanic areas under the sea
 Wall-less Bacteria
• Mycoplasmas
• A tiny bacterium bounded by a plasma membrane but
lacking a typical bacterial cell wall
• Live in soil, sewage, or are parasitic on plants or
animals
 Gram-Negative
• Bacteria that does not retain Gram stain/do not have
peptidoglycan
 Gram-Positive
• Bacteria that do retain Gram stain/contain
peptidoglycan
Table 19-1, p. 376
Fig. 19-12, p. 375