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• Molly Hunter• 641C Marley• 621-9350• [email protected]• Will have office hours Wed. Feb 1,
Fri. Feb 3 (next week)• Or make an appt. by email or phone• Lecture style: questions, questions• Key concepts/outline posted before
lecture , ppt posted after lecture
Prokaryotes
• Why you should care aboutthe little stuff
• Today - two of the threedomains of life
Outline of lecture today
I. Prokaryotes - Bacteria andArchaeaA. The three domains of life,phylogenyB. MorphologyC. Physiology/metabolismC. Ecology and key adaptationsD. A few prokaryotic groups
II. The evolution of the eukaryoticcell
Just like organization of life (cells,tissues….populations,communities), the organization ofgroups of organisms is hierarchical
Dom
ain
King
dom
Phyl
umCl
ass
Ord
erFa
mily
Spec
ies
Gen
us
How can we reconstruct theevolution of living things?(Chapter 25…)
• Systematists study evolutionaryrelationships
• Look for shared derived(=different from ancestor) traitsto group organisms
• Evidence used: morphology,development, and molecular data(especially DNA sequences)
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Why can’t we figure it outperfectly?
• More distant history is obscuredby more changes
• Among oldest lineages ofBacteria and Archaea inparticular, lots of “lateral genetransfer.” Makes it difficult toinfer relationships fromphylogeny of single genes.
A. Phylogeny
• The three domains: Bacteria,Archaea, and Eukarya.
~3 billion years
~2 billion years
A. Phylogeny
The Archaea and Bacteria areboth prokaryotic,but differmore from each other than does theArchaea from the Eukarya(=plants, animals, fungi, protists).
How did we learn the existenceof the Archaea?
• Difference betweenprokaryotes andeukaryotes long beenknown.
• Bacteria and Archaea aresuperficially similar
• But they are geneticallydifferent:u The first Archaean genome
was sequenced in 1996 -most genes were verydifferent from bacterialgenes - birth of the “threedomain” concept
I. Prokaryotes - Bacteriaand Archaea• The prokaryotes are the most
numerous organisms on Earth
•With tremendous diversity in metabolism, habitats
B. Morphology of prokaryotes
What are theymissing?
NucleiMembrane-enclosed
organellesCytoskeletons (actin
and microtubules)What have they got
that’s different fromprotists and animals?
Cell wall
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B. Morphology of theprokaryotes
Prokaryotic cells areusually muchsmaller thaneukaryotic cells
Closer to the size of amitochondrion orchloroplast
Is that a coincidence?
EukaryoteCell
ProkaryoteCell
B. Morphology of theprokaryotes - Movement
cyanobacteria
Gas vesicles toadjustbuoyancy
spirochaete
Or glidingmechanisms
Simpleflagella
B. Morphology of theprokaryotes - Cell walls• Prokaryotic cell walls differ from
those of eukaryotes.• Cell walls of Bacteria contain
peptidoglycan (a polymer of aminosugars). Cell walls of Archaeacontain proteins.
Bacterialcell wall
C. Ecology of the prokaryotes
• How do prokaryotes reproduce?• Asexually by fission
C. Physiology/metabolism ofthe prokaryotes
• How do prokaryotes reproduce?• Asexually by fission• Exchange genetic information
(e.g. by conjugation). Inconjugation,DNA travelsfromdonor torecipientvia acytoplasmicbridge
C. Physiology/metabolism ofprokaryotes
• Prokaryotes - fairly narrow rangeof shapes and sizes, not veryexciting movement: What haveprokaryotes been doing for morethan 3 billion years?
• Learning chemical tricks
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C. Physiology/metabolism ofprokaryotes
• All ancestral prokaryotes wereanaerobic, and some still are:
• Anaerobic: metabolism in theabsence of oxygen
• Aerobic: metabolism that requiresoxygen
• Some can shift back and forth
C. Physiology/metabolism ofprokaryotes
• All living organisms need a sourceof energy and a source of carbon inorder to survive and grow
• What is the source of our energyand carbon?
• We ingest molecules for bothenergy and carbon, so we’reheterotrophs
• Most Bacteria and Archaea areheterotrophs as well
C. Physiology/metabolism ofprokaryotes
• What do plants do for energy andcarbon?
• They use light for energy and C02for carbon. Some prokaryotes doas well - e.g. Cyanobacteria. Theseare autotrophs
• Why wereCyanobacteria soimportant in thehistory of lifeon Earth?
C. Physiology/metabolism ofProkaryotes
• Others have completely uniquesolutions, not found in eukaryotes
• Some use simple nitrogen or sulfurcompounds for energy, but CO2 forcarbon (needing neither light nororganic compounds for food!).
• Called chemolithotrophs• Have enabled life in extremely
inhospitable places!
C. Physiology/metabolism ofthe prokaryotes
• Some chemolithotrophslive near deep seahydrothermal vents at upto 2,500 m deep wherethere is no light.
• Prokaryotes (mostlyArchaea)that use hydrogensulfide from deep seavolcanic vents for energyprovide food foran entire bizarrecommunity.
C. Physiology/metabolism ofthe prokaryotes
Lastly, someuse light for energy,
but need food forcarbon:photoheterotrophs
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C. Physiology/metabolism ofthe prokaryotes
• Other chemical tricks• Fix nitrogen from
atmosphere• Digest cellulose• Produce amazing
toxinslike polyketides(many antibiotics,e.g. tetracycline,anti-tumor drugs)
• Polyketide inPaederus Paederus beetle
C. Physiology/metabolism ofthe prokaryotes
• Paederus has longbeen known becauseif crushed againstskin causes rashes
• Produces pederin, apolyketide
• Pederin also hasanti-tumor activity
• Guess wherePaederus gets itspederin?
Paederus beetle
D. Ecology of the prokaryotes- extreme habitats
• Some Archaea areheat-loving and acid-loving.
• Some live in hotsulfur springs and dieof “cold” at 131°F(55°C) Archaea
insulfurousvolcanicvent
D. Ecology of the prokaryotes
• Some anaerobic Archaea producemethane from CO2 as a key part oftheir energy metabolism.
• They account for the methane in theatmosphere.
D. Ecology of the prokaryotes
Some of these methane producers live inthe guts of herbivorous animals
D. Ecology of the prokaryotesMore about those prokaryotes in
mammalian guts - the humangut flora
How many cells relative to othercells in our body?
About how many species ofbacteria?
How much of your weight isbacteria?
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D. Ecology of the prokaryotesRole of gut flora?Long thought to be commensal - i.e.
beneficial to the bacteria, neutral for usRecent research tells a very different
storyE.g. bacteria are important for digesting
carbohydrates, and variation inefficiencies between individuals mayexplain variation in tendencies towardsobesity
Also influence immune system (andautoimmune diseases) in development
D. Ecology of theprokaryotes
• Some prokaryotes play key roles inglobal nitrogen cycles. E.g., nitrogenfixers, nitrifiers, and denitrifiers.
Nitrogen fixation –out of the air
Fig. 37.8 in your text
Nitrification – from one solid form to another better for plants
Denitrification –back to the air
E. Important prokaryoticgroups - just a few
• There are far more knownBacteria than Archaea.
The BacteriaThe Proteobacteria• By far the biggest
group of Bacteria• Includes Rhizobium,
the nitrogen fixingbacterium found inlegume root nodules.
• Also Salmonella,cholera, and E. coli.
The BacteriaThe Proteobacteria
Mitochondria evolvedfrom Proteobacteriaby endosymbiosis.
• Cyanobacteria arephotosynthetic
The Bacteria:Cyanobacteria
•Chloroplasts evolvedfrom cyanobacteria byendosymbiosis
•They created the oxygen atmosphere
•Makes youthink differentlyabout “pond scum,” no?
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The Bacteria: Spirochaetes
• Spirochaetes arecorkscrew shaped
•Some are parasitesof humans, e.g.agent causingsyphilis, Lymedisease
•Move by axialfilaments
The Bacteria: Chlamydias
Chlamydia are amongthe tiniest livingthings.
Almost all parasites,e.g. a sexuallytransmitted disease ofhumans
Have complex lifecycle with two stages:a resting stage getstaken intohost cell, the othergrows and divides
E. Important prokaryotic groups :Summary of the Archaea
• Archeans differ from Bacteria:Cell wall: proteins notpeptidoglycans
•Archeans often live in extreme habitats: tolerate high temperature, salt, low pH, absence of oxygen.
•Very different genetically
II. The origin of theeukaryotic cell
• Step 1? (no one knows thesequence) Increase in size
• A central problem with being big isthat surface area doesn’t increase asfast as volume, yet surfaces areneeded for gas exchange andfeeding
• What’s the solution?
II. The origin of theeukaryotic cell
What’s the solution?
Lose the cell wall,allow infoldingof the plasmamembrane toincrease area
The origin of the eukaryotic cell
This allowed cell to change shape and move things around
Step 3? A primitive cytoskeleton of actin and microtubules evolved.
Step 2? Infolded plasma membrane attached to the chromosome may have led to a nuclear envelope.
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II. The origin of theeukaryotic cell
• The first eukaryotes wereanaerobic.
• But as oxygen increased, theoxidizing atmosphere waspoisonous to anaerobes.
• Step 4? Engulfing an aerobicproteobacterium resulted inmitochondria.
• (Step 5? For some) Someorganisms engulfedcyanobacteria and becomephotosynthetic(chloroplasts).