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BIOLOGY
Chapter 20: pp. 354 - 372
10th Edition
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b. Bacilli:
Bacillus anthracis
SEM 35,000X
b: © Gary Gaugler/Visuals Unlimited;
20 nm
TEM 500,000X
Tobacco mosaic virus: RNA virus with a helical capsid.
Sylvia S. Mader
Viruses, Bacteria
and Archaea
Influenza virus: RNA virus with a helical capsid surrounded by an
envelope with spikes.
spikes
RNA
capsid
envelope
RNA
c.
capsid
d.
a: © Dr. Hans Gelderblom/Visuals Unlimited; b: © Eye of Science/Photo Researchers, Inc. c: © Dr. O. Bradfute/Peter Arnold, Inc.; d: © K.G. Murti/Visuals Unlimited
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
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1
Outline

Viruses




Structure
Classification
Reproduction
Prokaryotes



Structure
Reproduction
Nutrition

Bacteria
 Archaea
2
The Viruses





Are associated with a number of plant,
animal, and human diseases
Can only reproduce using the metabolic
machinery of the host cell
Are noncellular;
May have a DNA or RNA genome.
With the invention of the electron
microscope, these infectious agents could
be seen.
3
The Viruses: Structure
Generally smaller than 200 nm in diameter
 Each type has at least two parts


Capsid: Outer layer composed of protein
subunits
Some enveloped by membrane
 Others “naked”



Nucleic acid core: DNA or RNA
Vary in shape from thread-like to polyhedral
4
The Viruses: Structure
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Capsid (protein)
Covering
Envelope (not found in all viruses)
Virus particle
Nucleic acid molecule (DNA or RNA)
Inner core
Various proteins (enzymes)
5
Viruses
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Adenovirus: DNA virus with a polyhedral
capsid and a fiber at each corner.
TEM 80,000X
TEM 90,000X
T-even bacteriophage: DNA virus with a
polyhedral head and a helical tail.
fiber protein
capsid
fiber
DNA
protein unit
neck
tail sheath
DNA
capsid
tail fiber
pins
a.
base plate
b.
20 nm
TEM 500,000X
Tobacco mosaic virus: RNA virus with a helical capsid.
Influenza virus: RNA virus with a helical capsid surrounded by an
envelope with spikes.
spikes
RNA
capsid
envelope
RNA
c.
capsid
d.
a: © Dr. Hans Gelderblom/Visuals Unlimited; b: © Eye of Science/Photo Researchers, Inc. c: © Dr. O. Bradfute/Peter Arnold, Inc.; d: © K.G. Murti/Visuals Unlimited
6
Viral Categorization

Classification is based on:
Type of nucleic acid
 Size and shape
 Presence / absence of outer envelope

7
Parasitic Nature

Viruses are:
Obligate intracellular parasites
 Cannot reproduce outside a living cell
 Can be cultured only inside living cells

Chicken egg
 Tissue culture

8
“Growing” Viruses
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© Ed Degginger/Color Pic Inc.
9
Viral Reproduction

Gain entry into specific host cell


Viral nucleic acid then enters a cell


Capsid (or spikes of the envelope) adhere to
specific receptor sites on the host cell surface.
Viral genome codes for production of protein
units in the capsid.
Relies on host cell enzymes, ribosomes,
transfer RNA (tRNA), and ATP for its own
replication
10
The Bacteriophages: Reproduction

Bacteriophages – Viruses that infect
bacterial cells
Portions of capsid adhere to specific receptor
on the host cell
 Viral nucleic acid enters the cell
 Once inside, the virus takes over metabolic
machinery of the host cell

11
Bacteriophages: The Lytic Cycle

Lytic cycle may be divided into five stages:
Attachment
 Penetration
 Biosynthesis
 Maturation
 Release

12
The Bacteriophages: The Lysogenic Cycle

Phage becomes a prophage
Becomes integrated into the host genome
 Becomes latent
 May later reenter the lytic cycle

13
Lytic and Lysogenic Cycles in Prokaryotes
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1. ATTACHMENT
Capsid combines with receptor.
bacterial
cell wall
nucleic acid
bacterial
DNA
capsid
2. PENETRATION
Viral DNA enters host.
5. RELEASE
New viruses leave host cell.
INTEGRATION Viral DNA is integrated
into bacterial DNA and then is passed
on when bacteria reproduce.
LYTIC
CYCLE
viral
DNA
viral
DNA
LYSOGENIC
CYCLE
4. MATURATION
Assembly of viral components.
3. BIOSYNTHESIS
Viral components are synthesized.
prophage
daughter cells
14
Health Focus: Flu Viruses

A flu virus has an H (hemagglutinin) spike and an
N (neuraminidase) spike

H spike allows the virus to bind to the receptor


N spike attacks host plasma membranes




16 different types
Allows mature viruses to exit the cell
9 different types
Each type of spike can occur in different varieties
called subtypes.
Our immune system only recognizes H spikes and N
spikes it has been exposed to.
15
Spikes of Bird Flu Virus
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capsid
RNA genome
envelope
N (neuraminidase)
spike
H (hemagglutinin)
spike
mutation 1
mutation 2
a. Viral genetic mutations occur in a bird host
Human
flu virus
Bird
Flu
virus
combination
In host cell
b. Combination of viral genes occurs in human host
16
Reproduction of Animal Viruses
Animal virus enters the host cell
 Uncoating releases viral DNA or RNA


Budding:
Viral particles released in a bud
 Acquires a membranous envelope


Retroviruses (AIDS)
Contain reverse transcriptase
 Carries out RNA  cDNA reverse transcription
 cDNA becomes integrated into host DNA



Replicated as host DNA replicates
Viral DNA is transcribed; new viruses are produced
17
Reproduction of the Retrovirus HIV-1
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1. Attachment
receptor
envelope
spike
2. Entry
capsid
nuclear
pore
3. Reverse transcription
viral RNA
reverse transcriptase
cDNA
Integration
host DNA
ribosome
4. Biosynthesis
ER
viral
mRNA
provirus
viral
enzyme
capsid
protein
5. Maturation
viral RNA
6. Release
18
Viral Infections

Viruses are best known for causing infectious
diseases in plants and animals

Herpes, HIV, cancer


Viroids



Viruses lack metabolism; thus, antibiotics have no effect
Naked strands of RNA
Many crop diseases
Prions


Protein molecules with contagious tertiary structure
Some human and other animal diseases - Mad cow disease
19
The Prokaryotes

Include bacteria and archaea, which are
fully functioning cells
A single spoonful of earth can contain >1000
prokaryotes
 Range in size from 1-10 µm in length and
0.7-1.5 µm in width

20
Pasteur’s Experiment
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HYPOTHESIS A: Bacteria arise spontaneously in a broth.
HYPOTHESIS B: Bacteria in the air contaminate a broth.
FIRST EXPERIMENT
SECOND EXPERIMENT
flask is open to air
flasks outside building
opened briefly
boiling to
sterilize
broth
89% show growth
boiling to
sterilize
broth
air here is pure
air enters here
flasks inside building
opened briefly
boiling to
sterilize
broth
bacteria collect here
32% show growth
CONCLUSION:
Hypothesis B is supported because relative concentrations of bacteria in
the air explain the results.
100% have no growth
CONCLUSION:
Hypothesis B is supported because when air reaching the broth contains
no bacteria, the flask remains free of growth.
21
Prokaryote Structure
Lack a membrane-bounded nucleus (DNA
in nucleoid region)
 Outer cell wall containing peptidoglycan
 Some move by means of flagella
 Lack membranous organelles
 May have accessory ring of DNA (plasmid)

22
Prokaryote Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Prokaryotic cell
Cell envelope
Glycocalyx
Cell wall
Plasma membrane
Cytoplasm
Nucleoid
Ribosomes
Thylakoids (cyanobacteria)
Appendages
Flagella
Conjugation pilus
Fimbriae
23
Flagella
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TEM 13,250X
hook
filament
capsule
cell wall
basal
body
plasma
membrane
© RDF/Visuals Unlimited
24
BACTERIA & VIRUSES
Prokaryotic vs. Eukaryote Flagella
Binary Fission
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cytoplasm
cell wall
nucleoid
0.5 µm
© CNRI/SPL/Photo Researchers, Inc.
26
Reproduction in Prokaryotes

Asexual


Prokaryotes reproduce asexually by means of
binary fission
Methods of genetic recombination

Conjugation
Sex pilus forms between two cells
 Donor cell passes DNA to recipient cell through
pilus

Transformation…
 Transduction…

27
Fimbriae and Sex Pilus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
epithelial cell of intestinal villus
bacterium
a.
bacterium with fimbriae
flagellum
conjugation pilus
fimbriae
b.
5 µm
1 µm
a: Courtesy USDA, photo by Harley W. Moon; b: Courtesy C. Brinton, Jr.
28
Reproduction in Prokaryotes

Transformation
Occurs when bacterium picks up free pieces of
DNA from other prokaryotes
 Becomes incorporated into genome


Transduction
Occurs when bacteriophages carry portions of
bacterial DNA from one cell to another
 Serve as vectors


Some bacteria form resistant endospores
under unfavorable conditions
29
BACTERIA & VIRUSES
Spore Forming Bacteria:
Endospores
 NOT a form of reproduction
 One endospore per cell
 Contain chromosome & small amount
cytoplasm
 Allow germination after decades or
centuries
BACTERIA & VIRUSES
B. subtilis
B. anthracis
The Endospore of Clostridium tetani
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
endospore
© Alfred Pasieka/SPL/Photo Researchers, Inc.
32
Prokaryotic Nutrition

Oxygen requirements:
Obligate aerobes – unable to grow in the
absence of free oxygen
 Obligate anaerobes – unable to grow in the
presence of free oxygen
 Facultative anaerobes – able to grow in either
the presence or absence of free oxygen

33
Autotrophic Prokaryotes

Photoautotrophs
Use solar energy to reduce carbon dioxide to
organic compounds
 Photosynthetic


Chemoautotrophs
Oxidize inorganic compounds to obtain the
necessary energy
 Use it to reduce CO2 to an organic compound
 Chemosynthetic

34
Heterotrophic Prokaryotes

Most prokaryotes are chemoheterotrophs
that take in organic nutrients
Aerobic saprotrophs decompose most large
organic molecules to smaller molecules
 Essential components of healthy ecosystem


May be free-living or symbiotic
Nitrogen fixation
 Commensalism
 Parasites

35
Nodules of a Legume
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
root
nodule
Courtesy Nitragin Company, Inc.
36
The Bacteria

Bacteria are the more common type of
prokaryote.


Over 2,000 different bacteria have been named.
Most bacterial cells are protected by a cell
wall

Contains peptidoglycan
37
BACTERIA & VIRUSES
Gram
Pos.
Cell
Wall
BACTERIA & VIRUSES
Gram
Neg.
Cell
Wall
The Bacteria
Bacteria are commonly diagnosed using
the Gram stain procedure
 When washed after staining:

Gram-positive bacteria retain dye and appear
purple
 Gram-negative bacteria do not retain dye and
appear pink

40
BACTERIA & VIRUSES
GRAM STAIN
BACTERIA & VIRUSES
Gram + Cocci
Gram - Bacilli
The Bacteria
Structure of cell wall also of diagnostic use
 Bacteria can be further classified in terms
of their three basic shapes

Spiral (spirilli), Spirochaete
 Rod (bacilli), and
 Round (cocci)
 Vibrio (comma)

43
BACTERIA & VIRUSES
Diversity of Bacteria
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a. Spirillum:
Spirillum volutans
SEM 3,520X
b. Bacilli:
Bacillus anthracis
SEM 35,000X
c. Cocci:
SEM 6,250X
Streptococcus thermophilus
a: © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited; b: © Gary Gaugler/Visuals Unlimited; c: © SciMAT/Photo Researchers, Inc.
45
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46
Cyanobacteria
Formerly called the Blue-Green algae
(Cyanophyta)
 Cyanobacteria are Gram-negative bacteria
that photosynthesize
 Believed to be responsible for introducing
oxygen into the primitive atmosphere

Lack visible means of locomotion
 Can live in extreme environments
 When commensals with fungi, form lichens

47
Diversity Among the Cyanobacteria
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DNA thylakoids
plasma
membrane
cell wall
storage
granule
a. Gloeocapsa
LM 250X
b. Oscillatoria
LM 100X
c. Oscillatoria cell
a: © Michael Abbey/Photo Researchers, Inc.; b: © Tom Adams/Visuals Unlimited
48
The Archaea

Archaea were earlier considered bacteria

Carl Woese


discovered that the base sequence of their
rRNA differs from Bacteria
Other differences:
Archaea do not have peptidoglycan in their cell
walls like the Bacteria
 Archaea biochemical more like Eukarya than
Bacteria


Archaea now thought to be more closely
related to Eukarya than to Bacteria
49
Archaea Metabolism
Most are chemoautotrophs
 Some mutualistic
 Some commensalistic
 None known to be parasitic
 None are photosynthetic
 Many live in harsh conditions

50
Types of Archaea

Many live in harsh conditions:

Anaerobic marshes



Salty lakes



Methanogens
Produce methane from hydrogen gas and carbon dioxide
Halophiles
Require high salt concentrations for growth, and
Hot sulfur springs



Thermoacidophiles
Reduce sulfides and survive best at temperatures above 80ºC
Plasma membranes contain unusual lipids convey tolerance of
high temperatures
51
Archaebacteria vs. Eubacteria
•Cell Wall
Eubacteria: Peptidoglycan
Archaebacteria: No peptidoglycan
•Plasma Membrane:
Eubacteria: Lipids in bilayer
“ester-linked’.
Archaebacteria: “Ether-linked”
52
BACTERIA & VIRUSES
Archaebacteria vs. Eubacteria
•GENE TRANSFER MACHINERY:
Eubacteria: Ribosomal proteins &
RNA polymerase different from
Eukaryotes.
Archaebacteria: Ribosomal protein
& RNA is SIMILAR to eukaryotes
BACTERIA & VIRUSES
Archaebacteria vs. Eubacteria
•GENE ARCHITECTURE:
Eubacteria: No Introns
Archaebacteria: Sometimes Introns
BACTERIA & VIRUSES
PROKARYOTE VS. EUKARYOTE
1. Multicellularity
2. Cell Size
3. Chromosomes
4. Cell Division/Genetic Recombination
A. Asexual Division:
a. Binary Fission
b. Fragmentation
c. Budding
BACTERIA & VIRUSES
Bacterial Growth Curve
BACTERIA & VIRUSES
BACTERIAL GROWTH
1. Lag Phase:
Intense synthesis of enzymes & AA
Bacteria adjusting to new substrate
2. Log Phase:
Exponential growth
N(t) = N(0)2n
3. Stationary Phase:
Equilibrium achieved
death = replication
BACTERIA & VIRUSES
BACTERIAL GROWTH
3. Stationary Phase:
Essential nutrient depleted
Toxic byproducts
Physiologic Change occurs
Metabolism becomes unbalanced
Gram staining variable
Peptidoglycan cell wall deteriorates
BACTERIA & VIRUSES
BACTERIAL GROWTH
4. Death Phase:
Death rate exceeds replication
Bacteria decrease exponentially
BACTERIA & VIRUSES
MEASURING BACTERIAL GROWTH
1. Viable Counts:
Each bacterium produces colony
CFU’s
2. Turbidity:
Spectrophotometry
Higher population, less transmission
3. Analysis of Cellular Components
Measure amount of DNA, Protein, etc.
BACTERIA & VIRUSES
Viable counts
Utilize serial
Dilutions.
Count the
CFU’s
BACTERIA & VIRUSES
MEASURING BACTERIAL GROWTH
1. Viable Counts:
Each bacterium produces colony
CFU’s
2. Turbidity:
Spectrophotometry
Higher population, less transmission
3. Analysis of Cellular Components
Measure amount of DNA, Protein, etc.
BACTERIA & VIRUSES
Spectrophotometric analysis
measures the turbidity of a
solution
BACTERIA & VIRUSES
MEASURING BACTERIAL GROWTH
4. Analysis Metabolic Products:
Measure consumption substrate
Measure substance produced
e.g. Lactic acid
Bacterial Diseases in Humans
65
Viral Diseases in Humans
66