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VIRUSES, BACTERIA &
ARCHAEA
VIRUSES
Viruses are non-living infectious particles
Lack cellular organization
Lack growth
Lack metabolic abilities
Energy production
Waste generation
Require a host cell for replication
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Viral Structure
Nucleic acid in a protein coat
Nucleic acid can be DNA or RNA
Protein coat = capsid
May be surrounded by an envelope
Size
~10-200 nm
Slide 17
Fig. 22.16, p. 364
viral RNA
protein subunits of coat
18-nm diameter,
250-nm length 80-nm diameter
lipid envelope; proteins span the envelope, line its inner surface, and spike out above it
viral RNA
reverse transcriptase
viral coat (proteins)
100-120 nm diameter
DNA
protein coat
sheath
base plate
tail fiber
65-nm diameter head,
225-nm total length 3
Examples of viruses
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Tobacco mosaic virus Bacteriophage
Influenzavirus
Adenovirus
Herpesvirus
Quick Quiz: True or false: A virus is a
living organism.
A) True
B) False
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Quick Quiz: A virus is not considered a
living organism because it cannot do
which of these functions?
A) Grow
B) Reproduce
C) Metabolize
D) Respond to their environment
E) All of the above
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Viral Replication
Steps in Viral Replication:
Attachment to host cell
Penetration of host cell
Replication and synthesis of nucleic acids
and proteins
Assembly of viral components
Release of new viral particles
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Viral Replication
Steps in Viral Replication:
Attachment to host cell
Penetration of host cell
Replication and synthesis of nucleic acids
and proteins
Assembly of viral components
Release of new viral particles
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Figure 20-5 p326
A4 Viral enzyme excises viral DNA from chromosome.
C Viral proteins self-assemble into a coat around viral DNA.
D Accessory parts are attached to viral coat.
B Host replicates viral genetic material, builds viral proteins.
A3 Cell divides; recombinant DNA in each descendant cell.
A2 Chromosome and integrated viral DNA are replicated.
Lysogenic
Pathway
Lytic
Pathway
A1 Viral DNA is inserted into host chromosome by viral enzyme action.
A Viral particle binds, injects genetic material. E Lysis of host cell lets
new viral particles escape.
Reproduction of Bacteriophage
Reproductive cycles
Lytic vs. lysogenic cycles
Quick Quiz: True or false: During the
lysogenic cycle, a virus’s DNA is
incorporated into a host cell’s genome.
A) True
B) False
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(following animation)
Quick Quiz: My mom just got shingles,
which is a localized recurrence of the
chickenpox virus, varicella zoster. If
you have chickenpox as a child, then
you can get shingles as an adult.
Which cycle does varicella zoster use?
A) Lytic
B) Lysogenic
C) Both lytic and lysogenic
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Replication of DNA Viruses of
Plants & Animals
Examples
Polio, rabies, chickenpox, herpes, influenza
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Replication of RNA Viruses
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VIROIDS & PRIONS
Viroids
Infectious RNA
Cause of Hepatitis D
Prions
Infectious proteins
Kuru
Scrapie
CJD (Creutzfeldt-Jakob disease)
Bovine spongiform encephalopathy (“mad
cow”): variant CJD (vCJD)
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Quick Quiz: Which of the following is a
living organism?
A) Virus
B) Prion
C) Prokaryote
D) Viroid
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Quick Quiz: Why was “prokaryote” the
right choice on the previous slide?
A) It is the only one that has DNA
B) It is the only one that is cellular
C) It is the only one that has proteins
D) All of the above
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PROKARYOTES
Taxonomy
Domain: Archaea Bacteria
Kingdom: Archaebacteria Eubacteria
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Prokaryotic vs. Eukaryotic Cells
Component Prokaryote Eukaryote
Plasma membrane yes yes
Cell wall most some
DNA circular linear
Nucleus no (nucleoid) yes
Membrane-bound no yes
organelles
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General Characteristics of Prokaryotes
Unicellular
Unique cell structure & organization
Extremely diverse metabolic abilities
Most abundant organisms on the planet
Found in every habitat
Most are beneficial or benign
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Size
Range: 0.2 m – 5 mm (length)
Most ~ 1 m or smaller
Slide 1
Fig. 22.1, p. 354
100 µm 20 µm 0.5 µm
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Categorization of Prokaryotes
Cell shape
Cell wall properties
Thick – gram positive
Thin – gram negative
Metabolic abilities
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Prokaryote structure
Shape
Coccus (cocci)
Bacillus (bacilli)
Spirillum (spirochete)
Organization
Single
Chains
Clusters
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Gram-negative
Gram-positive
Metabolic Classes
Two ways to categorize organisms
metabolically
What is our carbon source?
Autotrophs
Heterotrophs
What is our energy source?
Phototrophs
Chemotrophs
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Metabolic Classes
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Metabolic Classes
Third way to categorize organisms
metabolically
How does the organism handle O2?
Aerobe – requires oxygen
Obligate anaerobe – cannot survive in oxygen
Facultative anaerobe – doesn’t need it, but can live
with it
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Quick Quiz: Prokaryotes may get their
energy in which of the following ways?
A) From the sun
B) From chemicals
C) From carbon dioxide
D) A and B
E) A and C
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Quick Quiz: You are a scientist who
has discovered a new kind of
prokaryote that lives deep in the
ocean, where it’s dark. What can you
definitely say about this organism?
A) It’s an autotroph
B) It’s a heterotroph
C) It’s a chemotroph
D) It’s a phototroph
E) It’s a photoautotroph
F) It’s a chemoheterotroph
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Fig. 21-8b, p. 340
cytoplasm,
with ribosomes
DNA, in
nucleoid region
pilus
flagellum
outer capsule
cell wall
plasma membrane
Prokaryote structure
Reproduction
Asexual
Binary fission
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Gene transfer
“Horizontal” gene transfer
Conjugation from other bacteria
Transduction from viruses
Transformation – naked DNA from environment
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sex pilus
Fig. 21-11, p. 341
nicked plasmid conjugation tube
Quick Quiz: Which of the following
processes does a bacterium use to
reproduce?
A) Conjugation
B) Binary fission
C) Transduction
D) Transformation
E) Infection
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Quick Quiz: If binary fission is
analogous to a couple having a baby,
then gene transfer is analogous to…
A) Cousins having a baby together
B) A person donating bone marrow to a stranger
C) Adopting a baby from a stranger
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Types of Eubacteria
Nitrogen fixers
N fixers nitrifiers denitrifiers
N2 ammonia nitrites & nitrates N2
Food fermentations
Lactic acid bacteria (e.g., lactobacilli)
Cheese, yogurt, pickles, sauerkraut
Pathogens
Salmonella enteritidis
Staphylococcus aureus
Clostridium botulinum
Streptococcus pyogenes 33
Types of Eubacteria
Thermophiles
“Heat lovers” – Thermus aquaticus
Cyanobacteria
Photosynthetic, produce atmospheric oxygen
Proteobacteria
Large, diverse group of bacteria
Gram-positive heterotrophs
Many produce endospores and/or toxins
Spirochetes & chlamydia
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Types of Archaebacteria
Extreme environments
Chemoautotrophs
Obtain energy from inorganic compounds
Examples:
Methanogens
Extreme thermophiles
Extreme halophiles
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Quick Quiz: Pathogens causing strep
throat, staph infections, and
salmonella food poisoning are…
A) Eubacteria
B) Archaebacteria
C) Prions
D) Viruses
E) All of the above
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Quick Quiz: Pathogens causing strep
throat, staph infections, and
salmonella food poisoning are…
A) Eubacteria
B) Archaebacteria
C) Prions
D) Viruses
E) All of the above
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