Chapter 27- Prokaryotes and Chapter 27- Prokaryotes and the Origin of Metabolismthe Origin of Metabolism

Key Points:Key Points:

1)1) The evolution of Prokaryotic metabolism was The evolution of Prokaryotic metabolism was both cause and effect of changing both cause and effect of changing environments on Earthenvironments on Earth

2)2) Molecular Systematics is leading to Molecular Systematics is leading to phylogenetic classification of prokaryotesphylogenetic classification of prokaryotes

3)3) Prokaryotes are indispensable links in the Prokaryotes are indispensable links in the recycling of chemical elements in ecosystemsrecycling of chemical elements in ecosystems

4)4) Many Prokaryotes are symbioticMany Prokaryotes are symbiotic5)5) Humans use Prokaryotes in research and Humans use Prokaryotes in research and

technologytechnology

Evolving metabolism is a cause Evolving metabolism is a cause and effect of changing and effect of changing

environmentsenvironments Nutrition and Metabolic Pathways Nutrition and Metabolic Pathways

evolved before Prokaryotesevolved before Prokaryotes Met with constantly changing physical Met with constantly changing physical

and biological environmentsand biological environments The evolved metabolic characteristics, The evolved metabolic characteristics,

in response to the change, in turn in response to the change, in turn effects the environment.effects the environment.

Studied through molecular systematics, Studied through molecular systematics, comparisons to other prokaryotes, and comparisons to other prokaryotes, and geological evidence.geological evidence.

Origins of MetabolismOrigins of Metabolism

Similar metabolic pathways in Similar metabolic pathways in prokaryotes indicate that metabolic prokaryotes indicate that metabolic processes developed early from an processes developed early from an ancient ancestorancient ancestor– Glycolysis and ATPGlycolysis and ATP

The First Prokaryotes that originated 3.5 The First Prokaryotes that originated 3.5 to 4.0 billion years ago were anaerobesto 4.0 billion years ago were anaerobes

Traditional Evolutionary Traditional Evolutionary HypothesisHypothesis

Earliest cells were chemoheterotrophsEarliest cells were chemoheterotrophs Absorbed free organic compounds such as Absorbed free organic compounds such as

ATPATP This depleted supply of free ATPThis depleted supply of free ATP Natural Selection prefers those organism Natural Selection prefers those organism

that produce their own ATPthat produce their own ATP Led to evolution of glycolysis and Led to evolution of glycolysis and

generation of ATP by substrate generation of ATP by substrate phosphorylationphosphorylation

Modern HypothesisModern Hypothesis

Find it unlikely that early Earth Find it unlikely that early Earth produced as much free ATP to produced as much free ATP to support the chemoheterotrophssupport the chemoheterotrophs

Chemoautotrophs instead of Chemoautotrophs instead of chemoheterotrophschemoheterotrophs

May have made energy through May have made energy through reacting compounds of iron and reacting compounds of iron and hydrogen sulfidehydrogen sulfide

FeS + H2S = FeS2 + H2 + free FeS + H2S = FeS2 + H2 + free energyenergy

Early source of energyEarly source of energy The free energy was used to split H2 into The free energy was used to split H2 into

protons and electrons to establish proton protons and electrons to establish proton gradientgradient

This gradient must have drive synthesis of This gradient must have drive synthesis of ATPATP

Natural Selection prefers those cells that Natural Selection prefers those cells that can manipulate hydrogen and establish can manipulate hydrogen and establish electron transport chainselectron transport chains

Origin of PhotosynthesisOrigin of Photosynthesis

In early prokaryotes, light-absorbing In early prokaryotes, light-absorbing pigments may have absorbed excess pigments may have absorbed excess energy and coupled with membrane energy and coupled with membrane proteins involved in ATP synthesis. proteins involved in ATP synthesis.

Best seen in modern archaea known Best seen in modern archaea known as extreme halophilesas extreme halophiles

HalophilesHalophiles

Contain a pigment known as Contain a pigment known as bacteriorhodopsin that absorbs light.bacteriorhodopsin that absorbs light.

It uses this energy to pump H+ ions It uses this energy to pump H+ ions across the membrane and generate across the membrane and generate gradientgradient

Drives the synthesis of ATPDrives the synthesis of ATP Simplest known form of Simplest known form of

photophosphorylationphotophosphorylation

Cont. Origins of PhotosynthesisCont. Origins of Photosynthesis

In some prokaryotes, pigments and In some prokaryotes, pigments and photosystems evolved to use light to photosystems evolved to use light to move electrons from H2S to NADP+.move electrons from H2S to NADP+.

This allows the potential fixation of This allows the potential fixation of CO2CO2

Don’t necessarily produce O2 yetDon’t necessarily produce O2 yet

CyanobacteriaCyanobacteria

bacteria that could use H20 instead bacteria that could use H20 instead of H2S as a source of electrons.of H2S as a source of electrons.

Also known as blue-green AlgaeAlso known as blue-green Algae Their ability to make organic Their ability to make organic

compounds from H20 allows for O2 compounds from H20 allows for O2 to be releasedto be released

Changed our worldChanged our world

Cyanobacteria and Oxygen Cyanobacteria and Oxygen RevolutionRevolution

Evolved 2.5 and 3.4 years agoEvolved 2.5 and 3.4 years ago Lived in marine ecosystemsLived in marine ecosystems Geology- marine sediments 2.5 Geology- marine sediments 2.5

billion years old are iron oxidebillion years old are iron oxide Thus, infer that O2 only entered the Thus, infer that O2 only entered the

atmosphere when all the dissolved atmosphere when all the dissolved iron was percipitatediron was percipitated

Origin of Cellular RespirationOrigin of Cellular Respiration

Increasing oxygen levels caused Increasing oxygen levels caused extinction of many prokaryotes.extinction of many prokaryotes.

Some prokaryotes evolved into Some prokaryotes evolved into organisms that could tolerate oxygenorganisms that could tolerate oxygen

Some even used the oxidizing Some even used the oxidizing property of O2 to pull electrons down property of O2 to pull electrons down electron chains.electron chains.

Some bacteria gave up photosynthesis Some bacteria gave up photosynthesis to become solely chemoheterotrophs.to become solely chemoheterotrophs.

Molecular Phylogeny related to Molecular Phylogeny related to the classification of prokaryotesthe classification of prokaryotes

Researchers first realized that the Researchers first realized that the domains, Archaea and Eukarya are domains, Archaea and Eukarya are different because each prokaryotic different because each prokaryotic domain has unique signature domain has unique signature sequencessequences

Signature sequences are taxon-Signature sequences are taxon-specific base sequences at specific base sequences at comparable locations on the comparable locations on the ribosomal RNA or other nucleic acids.ribosomal RNA or other nucleic acids.

Domain ArchaeaDomain Archaea

They inhabit the more extreme They inhabit the more extreme environments of Earthenvironments of Earth

This would require them to adapt to This would require them to adapt to the new environmental situations, the new environmental situations, and thus may have unique energy and thus may have unique energy metabolism .metabolism .

Researchers classify Archaea into Researchers classify Archaea into three groups: methanogens, extreme three groups: methanogens, extreme halophiles, and extreme halophiles, and extreme thermophiles.thermophiles.

Archaea- methanogensArchaea- methanogens

Have unique form of metabolism, because they Have unique form of metabolism, because they use H2 to reduce CO2 into methane (CH4).use H2 to reduce CO2 into methane (CH4).

Are Anaerobes that are poisoned by oxygenAre Anaerobes that are poisoned by oxygen Live in swamps and marshes, where microbes Live in swamps and marshes, where microbes

have already used up all the oxygenhave already used up all the oxygen Important decomposers in sewage treatmentImportant decomposers in sewage treatment Farmers found that they could use Farmers found that they could use

methanogens to convert garbage and dung methanogens to convert garbage and dung into methane, which could serve as a valuable into methane, which could serve as a valuable fuel.fuel.

Some reside in the guts of certain animals, Some reside in the guts of certain animals, whose diet mainly relies upon cellulose.whose diet mainly relies upon cellulose.

Archaea- extreme halophilesArchaea- extreme halophiles

Live in saline places such as Great Live in saline places such as Great Salt Lake and the Dead Sea.Salt Lake and the Dead Sea.

Some species are tolerant to salinity, Some species are tolerant to salinity, while other species actually require while other species actually require high salinity to undergo metabolismhigh salinity to undergo metabolism

Form a purple scum, a resultant of Form a purple scum, a resultant of bacteriorhodopsinbacteriorhodopsin

Archaea- Extreme thermophilesArchaea- Extreme thermophiles Live in hot environmentsLive in hot environments Temperature in environments is ideally 60 to 80 Temperature in environments is ideally 60 to 80

degrees Celsiusdegrees Celsius Sulfolobus is an extreme thermophile that Sulfolobus is an extreme thermophile that

thrives in the hot sulfur springs of Yellowstonethrives in the hot sulfur springs of Yellowstone Others live at deep-sea hydrothermal vents Others live at deep-sea hydrothermal vents

where water temperature is around 105 degrees where water temperature is around 105 degrees CelsiusCelsius

James Lake of UCLA has a theory that extreme James Lake of UCLA has a theory that extreme thermophiles are prokaryotes that are most thermophiles are prokaryotes that are most closely related to eukaryotes.closely related to eukaryotes.

He calls them eocytes, or “dawn cells”He calls them eocytes, or “dawn cells”

Domain BacteriaDomain Bacteria

Majority of all ProkaryotesMajority of all Prokaryotes Since Bacteria have diversified very long ago, Since Bacteria have diversified very long ago,

evolutionary connections between different evolutionary connections between different phylogenetic groups of Bacteria have been phylogenetic groups of Bacteria have been hard to distinguishhard to distinguish

Through molecular systematics, scientists Through molecular systematics, scientists have studied gene sequences to further have studied gene sequences to further subdivide the Bacteria domainsubdivide the Bacteria domain

Recently, Domain Bacteria was subdivided Recently, Domain Bacteria was subdivided into Proteobacteria, Gram-Positive Bacteria, into Proteobacteria, Gram-Positive Bacteria, Gram Positive Bacteria, Cyanobacteria, and Gram Positive Bacteria, Cyanobacteria, and Spirochetes.Spirochetes.

Ecological Impact of Ecological Impact of Prokaryotes- recycling of Prokaryotes- recycling of

chemical elementschemical elements Basic Principle- atoms in our bodies were Basic Principle- atoms in our bodies were parts of the inorganic molecules such as parts of the inorganic molecules such as soil, air and watersoil, air and water

Therefore, to continue life on Earth, these Therefore, to continue life on Earth, these chemical elements need to be recycled chemical elements need to be recycled between biological (organic) and chemical between biological (organic) and chemical (inorganic) parts of ecosystem(inorganic) parts of ecosystem

Thus, Bacteria such as decomposers are Thus, Bacteria such as decomposers are required to convert carbon, nitrogen and required to convert carbon, nitrogen and other elements essential to life between other elements essential to life between biological and physical systems.biological and physical systems.

Many prokaryotes are symbioticMany prokaryotes are symbiotic

Prokaryotes interact in groups, and rarely Prokaryotes interact in groups, and rarely by themselvesby themselves

Symbiosis is the ecological relationship Symbiosis is the ecological relationship between different species that are in direct between different species that are in direct contactcontact

Sybionts ae the organisms involved in Sybionts ae the organisms involved in symbiosissymbiosis

There are three categories of symbiosis: There are three categories of symbiosis: mutualism, commensalism, and parasitismmutualism, commensalism, and parasitism

Evolutionary context of Evolutionary context of symbiosissymbiosis

Symbiosis played a major role in Symbiosis played a major role in prokaryotic evolution and the origin prokaryotic evolution and the origin of early eukaryotesof early eukaryotes

Mitochondria have their own DNA in Mitochondria have their own DNA in eukaryotic cells, so scientists believe eukaryotic cells, so scientists believe mitochondria were early prokaryotes mitochondria were early prokaryotes with a symbiotic relationship with the with a symbiotic relationship with the cell.cell.

Prokaryotes and DiseaseProkaryotes and Disease

For pathogens to affect the body, they For pathogens to affect the body, they must resist all internal defenses of body must resist all internal defenses of body and harm the hostand harm the host

Opportunistic pathogens are parasitic Opportunistic pathogens are parasitic prokaryotes that normally live inside the prokaryotes that normally live inside the host, but cause illness when the host’s host, but cause illness when the host’s immune system is alteredimmune system is altered

German physician, Robert Koch, proposed German physician, Robert Koch, proposed the Koch Postulates, which lay the the Koch Postulates, which lay the guideless for modern medical microbiologyguideless for modern medical microbiology

Koch PostulatesKoch Postulates

To propose that a certain pathogen is To propose that a certain pathogen is related to a certain disease:related to a certain disease:– Researcher must find the same pathogen in each Researcher must find the same pathogen in each

individual with the same diseaseindividual with the same disease– Isolate pathogen from the diseased subject and Isolate pathogen from the diseased subject and

grow the microbe in a pure culturegrow the microbe in a pure culture– Induce disease in Experimental animals by Induce disease in Experimental animals by

transferring pathogen from the culture to the transferring pathogen from the culture to the animalanimal

– Isolate the same pathogen from experimental Isolate the same pathogen from experimental animals after disease/symptoms developsanimals after disease/symptoms develops

There are certain circumstances where Koch There are certain circumstances where Koch Postulates don’t workPostulates don’t work

Disease- ExotoxinsDisease- Exotoxins

Exotoxins are proteins secreted by Exotoxins are proteins secreted by prokaryotesprokaryotes

Produce really strong poisons, such Produce really strong poisons, such as botulism toxin, where a gram of as botulism toxin, where a gram of this sample can kill million peoplethis sample can kill million people

Linked to Botulism, Cholera, and Linked to Botulism, Cholera, and traveler's diarrheatraveler's diarrhea

Disease- EndotoxinsDisease- Endotoxins

Endotoxins are certain components Endotoxins are certain components of the outer membranes of certain of the outer membranes of certain bacteria that cause diseasebacteria that cause disease

Related to Salmonella.Related to Salmonella.