Biology in Focus - Chapter 24
Transcript of Biology in Focus - Chapter 24
CAMPBELL BIOLOGY IN FOCUS
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Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
24Early Life and the Diversification of Prokaryotes
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Earth formed 4.6 billion years ago The oldest fossil organisms are prokaryotes dating
back to 3.5 billion years ago Prokaryotes are single-celled organisms in the
domains Bacteria and Archaea Some of the earliest prokaryotic cells lived in dense
mats that resembled stepping stones
Overview: The First Cells
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Figure 24.1
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Prokaryotes are the most abundant organisms on Earth
There are more in a handful of fertile soil than the number of people who have ever lived
Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms
Some prokaryotes colonize the bodies of other organisms
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Figure 24.2
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Concept 24.1: Conditions on early Earth made the origin of life possible
Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into macromolecules
3. Packaging of molecules into protocells, membrane-bound droplets that maintain a consistent internal chemistry
4. Origin of self-replicating molecules
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Synthesis of Organic Compounds on Early Earth
Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, and hydrogen)
As Earth cooled, water vapor condensed into oceans, and most of the hydrogen escaped into space
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In the 1920s, A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment
In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible
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However, the evidence is not yet convincing that the early atmosphere was in fact reducing
Instead of forming in the atmosphere, the first organic compounds may have been synthesized near volcanoes or deep-sea vents
Miller-Urey-type experiments demonstrate that organic molecules could have formed with various possible atmospheres
Organic molecules have also been found in meteorites
Video: Hydrothermal Vent Video: Tubeworms
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Figure 24.3
Mas
s of
amin
o ac
ids
(mg)
Num
ber o
f am
ino
acid
s
1953 19532008
20
2008
10
0
200
100
0
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Figure 24.3a
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Abiotic Synthesis of Macromolecules
RNA monomers have been produced spontaneously from simple molecules
Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock
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Protocells
Replication and metabolism are key properties of life and may have appeared together
Protocells may have been fluid-filled vesicles with a membrane-like structure
In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer
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Adding clay can increase the rate of vesicle formation Vesicles exhibit simple reproduction and metabolism
and maintain an internal chemical environment
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Figure 24.4
Vesicleboundary
Precursormolecules only
1 m
Rel
ativ
e tu
rbid
ity, a
nin
dex
of v
esic
le n
umbe
r
(a) Self-assembly
Time (minutes)
0.4
0.2
00 20 40 60
Precursor molecules plusmontmorillonite clay
20 m(c) Absorption of RNA(b) Reproduction
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Figure 24.4a
Precursormolecules only
Rel
ativ
e tu
rbid
ity, a
nin
dex
of v
esic
le n
umbe
r
Time (minutes)
0.4
0.2
00 20 40 60
Precursor molecules plusmontmorillonite clay
(a) Self-assembly
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Figure 24.4b
20 m(b) Reproduction
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Figure 24.4c
Vesicleboundary
1 m
(c) Absorption of RNA
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Self-Replicating RNA
The first genetic material was probably RNA, not DNA
RNA molecules called ribozymes have been found to catalyze many different reactions For example, ribozymes can make complementary
copies of short stretches of RNA
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Natural selection has produced self-replicating RNA molecules
RNA molecules that were more stable or replicated more quickly would have left the most descendant RNA molecules
The early genetic material might have formed an “RNA world”
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Vesicles with RNA capable of replication would have been protocells
RNA could have provided the template for DNA, a more stable genetic material
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Fossil Evidence of Early Life
Many of the oldest fossils are stromatolites, layered rocks that formed from the activities of prokaryotes up to 3.5 billion years ago
Ancient fossils of individual prokaryotic cells have also been discovered For example, fossilized prokaryotic cells have been
found in 3.4-billion-year-old rocks from Australia
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Figure 24.5
Time (billions of years ago)
10 m30
m
5 cm
Nonphotosynthetic bacteria
Cyanobacteria
Stromatolites
Possibleearliestappearancein fossil record
4 3 2 1 0
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Figure 24.5a
Time (billions of years ago)
Nonphotosynthetic bacteria
Cyanobacteria
Stromatolites
Possibleearliestappearancein fossil record
4 3 2 1 0
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Figure 24.5b
30
m
3-billion-year-oldfossil of a cluster ofnonphotosyntheticprokaryote cells
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Figure 24.5c
5 cm1.1-billion-year-oldfossilized stromatolite
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Figure 24.5d
10 m
1.5-billion-year-old fossilof a cyanobacterium
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The cyanobacteria that form stromatolites were the main photosynthetic organisms for over a billion years
Early cyanobacteria began the release of oxygen into Earth’s atmosphere
Surviving prokaryote lineages either avoided or adapted to the newly aerobic environment
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Concept 24.2: Diverse structural and metabolic adaptations have evolved in prokaryotes
Most prokaryotes are unicellular, although some species form colonies
Most prokaryotic cells have diameters of 0.5–5 µm, much smaller than the 10–100 µm diameter of many eukaryotic cells
Prokaryotic cells have a variety of shapes The three most common shapes are spheres (cocci),
rods (bacilli), and spirals
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Figure 24.6
3 m
(a) Spherical (b) Rod-shaped (c) Spiral
1 m
1 m
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Figure 24.6a
(a) Spherical
1 m
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Figure 24.6b
(b) Rod-shaped
1 m
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Figure 24.6c
3 m
(c) Spiral
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Cell-Surface Structures
A key feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment
Eukaryote cell walls are made of cellulose or chitin Bacterial cell walls contain peptidoglycan, a network
of modified sugars cross-linked by polypeptides
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Archaeal cell walls contain polysaccharides and proteins but lack peptidoglycan
Scientists use the Gram stain to classify bacteria by cell wall composition
Gram-positive bacteria have simpler walls with a large amount of peptidoglycan
Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic
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Figure 24.7
Peptido-glycanlayer
Cellwall
Gram-negativebacteria
10 m
Gram-positivebacteria
(b) Gram-negativebacteria
(a) Gram-positivebacteria
Plasmamembrane Plasma membrane
Peptidoglycanlayer
Cellwall
Outermembrane
Carbohydrate portionof lipopolysaccharide
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Figure 24.7a
Peptido-glycanlayer
Cellwall
(a) Gram-positivebacteria
Plasmamembrane
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Figure 24.7b
(b) Gram-negativebacteria
Plasma membrane
Peptidoglycanlayer
Cellwall
Outermembrane
Carbohydrate portionof lipopolysaccharide
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Figure 24.7c
Gram-negativebacteria
10 m
Gram-positivebacteria
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Many antibiotics target peptidoglycan and damage bacterial cell walls
Gram-negative bacteria are more likely to be antibiotic resistant
A polysaccharide or protein layer called a capsule covers many prokaryotes
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Figure 24.8
Bacterialcell wall
Bacterialcapsule
Tonsilcell
200 nm
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Some bacteria develop resistant cells called endospores when they lack an essential nutrient
Other bacteria have fimbriae, which allow them to stick to their substrate or other individuals in a colony
Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA
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Figure 24.9
Fimbriae
1 m
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Motility
In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from a stimulus
Chemotaxis is the movement toward or away from a chemical stimulus
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Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends
Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently
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Figure 24.10
Flagellum
Filament 20 nm
HookMotorCell wall
RodPeptidoglycanlayer
Plasmamembrane
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Figure 24.10a
20 nm
Hook
Motor
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Evolutionary Origins of Bacterial Flagella
Bacterial flagella are composed of a motor, hook, and filament
Many of the flagella’s proteins are modified versions of proteins that perform other tasks in bacteria
Flagella likely evolved as existing proteins were added to an ancestral secretory system
This is an example of exaptation, where existing structures take on new functions through descent with modification
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Internal Organization and DNA
Prokaryotic cells usually lack complex compartmentalization
Some prokaryotes do have specialized membranes that perform metabolic functions
These are usually infoldings of the plasma membrane
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Figure 24.11
Respiratorymembrane
0.2 m 1 m
Thylakoidmembranes
(a) Aerobic prokaryote (b) Photosynthetic prokaryote
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Figure 24.11a
Respiratorymembrane
0.2 m
(a) Aerobic prokaryote
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Figure 24.11b
1 m
Thylakoidmembranes
(b) Photosynthetic prokaryote
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The prokaryotic genome has less DNA than the eukaryotic genome
Most of the genome consists of a circular chromosome
The chromosome is not surrounded by a membrane; it is located in the nucleoid region
Some species of bacteria also have smaller rings of DNA called plasmids
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Figure 24.12
Plasmids
1 m
Chromosome
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There are some differences between prokaryotes and eukaryotes in DNA replication, transcription, and translation
These allow people to use some antibiotics to inhibit bacterial growth without harming themselves
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Nutritional and Metabolic Adaptations
Prokaryotes can be categorized by how they obtain energy and carbon Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals
Autotrophs require CO2 as a carbon source
Heterotrophs require an organic nutrient to make organic compounds
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Energy and carbon sources are combined to give four major modes of nutrition Photoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy
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Table 24.1
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The Role of Oxygen in Metabolism
Prokaryotic metabolism varies with respect to O2
Obligate aerobes require O2 for cellular respiration
Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration, in which substances other than O2 act as electron acceptors
Facultative anaerobes can survive with or without O2
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Nitrogen Metabolism
Nitrogen is essential for the production of amino acids and nucleic acids
Prokaryotes can metabolize nitrogen in a variety of ways
In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)
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Metabolic Cooperation
Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells
In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products
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Figure 24.13
20 m
Heterocyst
Photosyntheticcells
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In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms
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Reproduction
Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours
Key features of prokaryotic biology allow them to divide quickly They are small They reproduce by binary fission They have short generation times
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Adaptations of Prokaryotes: A Summary
The ongoing success of prokaryotes is an extraordinary example of physiological and metabolic diversification
Prokaryotic diversification can be viewed as a first great wave of adaptive radiation in the evolutionary history of life
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Prokaryotes have considerable genetic variation Three factors contribute to this genetic diversity
Rapid reproduction Mutation Genetic recombination
Concept 24.3: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes
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Rapid Reproduction and Mutation
Prokaryotes reproduce by binary fission, and offspring cells are generally identical
Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population
High diversity from mutations allows for rapid evolution
Prokaryotes are not “primitive” but are highly evolved
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Figure 24.14 Experiment
0.1 mL(population sample)
Results
Daily serial transfer
Old tube(discardedaftertransfer)
New tube(9.9 mLgrowthmedium)
Popu
latio
n gr
owth
rate
(rel
ativ
e to
anc
estr
alpo
pula
tion)
Generation10,000 20,00015,0005,0000
1.8
1.6
1.4
1.2
1.0
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Figure 24.14a
ResultsPo
pula
tion
grow
th ra
te(r
elat
ive
to a
nces
tral
popu
latio
n)
Generation10,000 20,00015,0005,0000
1.8
1.6
1.4
1.2
1.0
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Genetic Recombination
Genetic recombination, the combining of DNA from two sources, contributes to diversity
Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation
Movement of genes among individuals from different species is called horizontal gene transfer
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Transformation and Transduction
A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation
Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
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Figure 24.15-1
1 Phage infects bacterialdonor cell with A andB alleles.
Donor cell
A B
Phage DNA
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Figure 24.15-2
2
1 Phage infects bacterialdonor cell with A andB alleles.
Phage DNA isreplicated andproteins synthesized.
Donor cell
A B
A B
Phage DNA
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Figure 24.15-3
3
2
1 Phage infects bacterialdonor cell with A andB alleles.
Phage DNA isreplicated andproteins synthesized.
Fragment of DNA withA allele is packagedwithin a phage capsid.
Donor cell
A
A
B
A B
Phage DNA
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4
3
2
1 Phage infects bacterialdonor cell with A andB alleles.
Phage DNA isreplicated andproteins synthesized.
Fragment of DNA withA allele is packagedwithin a phage capsid.
Phage with A alleleinfects bacterialrecipient cell.
Recipientcell
Crossing over
Donor cell
A− B−
A
A
A
B
A B
Phage DNAFigure 24.15-4
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Figure 24.15-5
Phage infects bacterialdonor cell with A andB alleles.
Incorporation of phageDNA creates recombinantcell with genotype AB.
Phage DNA isreplicated andproteins synthesized.
Fragment of DNA withA allele is packagedwithin a phage capsid.
Phage with A alleleinfects bacterialrecipient cell.
Recombinantcell
Recipientcell
Crossing over
Donor cell
A B−
A− B−
A
A
A
B
A B
Phage DNA
5
4
3
2
1
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Conjugation and Plasmids
Conjugation is the process where genetic material is transferred between prokaryotic cells
In bacteria, the DNA transfer is one way In E. coli, the donor cell attaches to a recipient by a
pilus, pulls it closer, and transfers DNA
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Figure 24.16
Sex pilus
1 m
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The F factor is a piece of DNA required for the production of pili
Cells containing the F plasmid (F+) function as DNA donors during conjugation
Cells without the F factor (F–) function as DNA recipients during conjugation
The F factor is transferable during conjugation
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Figure 24.17-1
1 One strand ofF cell plasmidDNA breaks atarrowhead.
Bacterialchromosome
Bacterialchromosome
F plasmid
Matingbridge
F cell(donor)
F− cell(recipient)
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Figure 24.17-2
21 One strand ofF cell plasmidDNA breaks atarrowhead.
Bacterialchromosome
Bacterialchromosome
F plasmid
Matingbridge
F cell(donor)
F− cell(recipient)
Broken strandpeels off andenters F− cell.
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Figure 24.17-3
321 One strand ofF cell plasmidDNA breaks atarrowhead.
Bacterialchromosome
Bacterialchromosome
F plasmid
Matingbridge
F cell(donor)
F− cell(recipient)
Broken strandpeels off andenters F− cell.
Donor andrecipient cellssynthesizecomplementaryDNA strands.
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Figure 24.17-4
4321 One strand ofF cell plasmidDNA breaks atarrowhead.
Bacterialchromosome
Bacterialchromosome
F plasmid
Matingbridge
F cell(donor)
F− cell(recipient)
F
cell
F
cell
Broken strandpeels off andenters F− cell.
Recipient cellis now arecombinantF cell.
Donor andrecipient cellssynthesizecomplementaryDNA strands.
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The F factor can also be integrated into the chromosome
A cell with the F factor built into its chromosomes functions as a donor during conjugation
The recipient becomes a recombinant bacterium, with DNA from two different cells
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R Plasmids and Antibiotic Resistance Genes for antibiotic resistance are carried in R
plasmids Antibiotics kill sensitive bacteria, but not bacteria with
specific R plasmids Through natural selection, the fraction of bacteria
with genes for resistance increases in a population exposed to antibiotics
Antibiotic-resistant strains of bacteria are becoming more common
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Concept 24.4: Prokaryotes have radiated into a diverse set of lineages
Prokaryotes have radiated extensively due to diverse structural and metabolic adaptations
Prokaryotes inhabit every environment known to support life
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An Overview of Prokaryotic Diversity
Applying molecular systematics to the investigation of prokaryotic phylogeny has produced dramatic results
Molecular systematics led to the splitting of prokaryotes into bacteria and archaea
Molecular systematists continue to work on the phylogeny of prokaryotes
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Figure 24.18
UNIVERSALANCESTOR
Dom
ainEukarya
Gram-positivebacteria
Cyanobacteria
Spirochetes
Chlamydias
Proteobacteria
Nanoarchaeotes
Crenarchaeotes
Euryarchaeotes
Korarchaeotes
Eukaryotes
Dom
ain Archaea
Dom
ain Bacteria
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The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes
A handful of soil may contain 10,000 prokaryotic species
Horizontal gene transfer between prokaryotes obscures the root of the tree of life
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Bacteria
Bacteria include the vast majority of prokaryotes familiar to most people
Diverse nutritional types are scattered among the major groups of bacteria
Video: Tubeworms
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Figure 24.UN01
Eukarya
BacteriaArchaea
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Figure 24.19a
Alpha subgroup Beta subgroup
Gamma subgroup Delta subgroup Epsilon subgroup
Rhizobium (arrows)(TEM)
Nitrosomonas(TEM)
Thiomargaritanamibiensis (LM)
Helicobacter pylori(TEM)
Chondromycescrocatus (SEM)
Proteo-bacteria
AlphaBetaGammaDeltaEpsilon
2.5
m
1 m
2 m
300
m
200
m
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Proteobacteria are gram-negative bacteria including photoautotrophs, chemoautotrophs, and heterotrophs
Some are anaerobic and others aerobic
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Figure 24.19aa
Proteobacteria
AlphaBetaGammaDeltaEpsilon
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Members of the subgroup alpha proteobacteria are closely associated with eukaryotic hosts in many cases
Scientists hypothesize that mitochondria evolved from aerobic alpha proteobacteria through endosymbiosis
Example: Rhizobium, which forms root nodules in legumes and fixes atmospheric N2
Example: Agrobacterium, which produces tumors in plants and is used in genetic engineering
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Figure 24.19ab
Alpha subgroupRhizobium (arrows)inside a root cell of a legume (TEM)
2.5
m
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Members of the subgroup beta proteobacteria are nutritionally diverse
Example: the soil bacterium Nitrosomonas, which converts NH4
+ to NO2–
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Figure 24.19ac
Beta subgroupNitrosomonas(colorized TEM)
1 m
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The subgroup gamma proteobacteria includes sulfur bacteria such as Thiomargarita namibiensis and pathogens such as Legionella, Salmonella, and Vibrio cholerae
Escherichia coli resides in the intestines of many mammals and is not normally pathogenic
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Figure 24.19ad
Gamma subgroupThiomargaritanamibiensis containingsulfur wastes (LM)
200
m
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The subgroup delta proteobacteria includes the slime-secreting myxobacteria and bdellovibrios, a bacteria that attacks other bacteria
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Figure 24.19ae
Delta subgroupFruiting bodies ofChondromyces crocatus,a myxobacterium (SEM)
300
m
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The subgroup epsilon proteobacteria contains many pathogens including Campylobacter, which causes blood poisoning, and Helicobacter pylori, which causes stomach ulcers
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Figure 24.19af
Epsilon subgroupHelicobacter pylori(colorized TEM)
2 m
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Figure 24.19b
Spirochetes Cyanobacteria
Gram-positive bacteria
Chlamydias
Leptospira(TEM)
Oscillatoria
Streptomyces(SEM)
Chlamydia (arrows)(TEM)
Mycoplasmas(SEM)
2.5
m
40
m
5 m
2 m
5 m
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Chlamydias are parasites that live within animal cells
Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission
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Figure 24.19ba
ChlamydiasChlamydia (arrows)inside an animal cell(colorized TEM)
2.5
m
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Spirochetes are helical heterotrophs Some are parasites, including Treponema pallidum,
which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease
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Figure 24.19bb
SpirochetesLeptospira,a spirochete(colorized TEM)
5 m
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Cyanobacteria are photoautotrophs that generate O2
Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis
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Figure 24.19bc
CyanobacteriaOscillatoria,a filamentouscyanobacterium
40
m
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Gram-positive bacteria include Actinomycetes, which decompose soil Streptomyces, which are a source of antibiotics Bacillus anthracis, the cause of anthrax Clostridium botulinum, the cause of botulism Some Staphylococcus and Streptococcus, which can
be pathogenic Mycoplasms, the smallest known cells
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Figure 24.19bd
Gram-positive bacteriaStreptomyces,the source ofmany antibiotics(SEM)
5 m
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Figure 24.19be
Gram-positive bacteriaHundreds of mycoplasmascovering a humanfibroblast cell(colorized SEM)
2 m
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Archaea
Archaea share certain traits with bacteria and other traits with eukaryotes
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Figure 24.UN02
Eukarya
BacteriaArchaea
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Table 24.2
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Table 24.2a
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Table 24.2b
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Some archaea live in extreme environments and are called extremophiles
Extreme halophiles live in highly saline environments
Extreme thermophiles thrive in very hot environments
Video: Cyanobacteria (Oscillatoria)
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Figure 24.20
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Methanogens produce methane as a waste product Methanogens are strict anaerobes and are poisoned
by O2
Methanogens live in swamps and marshes, in the guts of cattle, and near deep-sea hydrothermal vents
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Figure 24.21
2 m
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Figure 24.21a
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Figure 24.21b
2 m
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Recent metagenomic studies have revealed many new groups of archaea
Some of these may offer clues to the early evolution of life on Earth
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Concept 24.5: Prokaryotes play crucial roles in the biosphere
Prokaryotes are so important that if they were to disappear, the prospects for any other life surviving would be dim
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Chemical Recycling
Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems
Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms and waste products
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Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth
Prokaryotes can also “immobilize” or decrease the availability of nutrients
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Figure 24.22
Seedlings growing in the lab
Soil treatment
Upt
ake
of K
by
plan
ts (m
g)
Strain 1 Strain 2 Strain 3Nobacteria
1.0
0.8
0.6
0.4
0.2
0
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Figure 24.22a
Seedlings growing in the lab
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Ecological Interactions
Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont
Prokaryotes often form symbiotic relationships with larger organisms
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In mutualism, both symbiotic organisms benefit In commensalism, one organism benefits while
neither harming nor helping the other in any significant way
In parasitism, an organism called a parasite harms but does not kill its host
Parasites that cause disease are called pathogens
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Figure 24.23
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The ecological communities of hydrothermal vents depend on chemoautotrophic bacteria for energy
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Impact on Humans
The best-known prokaryotes are pathogens, but many others have positive interactions with humans
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Mutualistic Bacteria
Human intestines are home to about 500–1,000 species of bacteria
Many of these are mutualists and break down food that is undigested by our intestines
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Pathogenic Bacteria
Prokaryotes cause about half of all human diseases For example, Lyme disease is caused by a bacterium
and carried by ticks
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Figure 24.24
5 m
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Figure 24.24a
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Figure 24.24b
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Figure 24.24c
5 m
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Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins
Exotoxins are secreted and cause disease even if the prokaryotes that produce them are not present
Endotoxins are released only when bacteria die and their cell walls break down
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Horizontal gene transfer can spread genes associated with virulence
For example, pathogenic strains of the normally harmless E. coli bacteria have emerged through horizontal gene transfer
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Prokaryotes in Research and Technology
Experiments using prokaryotes have led to important advances in DNA technology For example, E. coli is used in gene cloning For example, Agrobacterium tumefaciens is used to
produce transgenic plants
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Bacteria can now be used to make natural plastics Prokaryotes are the principal agents in
bioremediation, the use of organisms to remove pollutants from the environment
Bacteria can be engineered to produce vitamins, antibiotics, and hormones
Bacteria are also being engineered to produce ethanol from waste biomass
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Figure 24.25
(a)
(b)
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Figure 24.25a
(a)
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Figure 24.25b
(b)
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Figure 24.26
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Figure 24.UN03
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Figure 24.UN04
FimbriaeCell wall
Capsule
Flagella
Sex pilus
Internalorganization
Circularchromosome
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Figure 24.UN05