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Prokaryotes Outline of Lecture Today How Can We Reconstruct the Evolution of Living Things? (Chapter 25…)

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Prokaryotes Outline of Lecture Today How Can We Reconstruct the Evolution of Living Things? (Chapter 25…) • 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 Outline of lecture today I. Prokaryotes - Bacteria and Archaea • Why you should care about A. The three domains of life, the little stuff phylogeny • Today - two of the three B. Morphology domains of life C. Physiology/metabolism C. Ecology and key adaptations D. A few prokaryotic groups II. The evolution of the eukaryotic cell Just like organization of life (cells, tissues….populations, How can we reconstruct the communities), the organization of evolution of living things? groups of organisms is hierarchical (Chapter 25…) • Systematists study evolutionary relationships Domain Kingdom • Look for shared derived Phylum Class (=different from ancestor) traits Order to group organisms Family Genus Species • Evidence used: morphology, development, and molecular data (especially DNA sequences) 1 A. Phylogeny Why can’t we figure it out • The three domains: Bacteria, perfectly? Archaea, and Eukarya. • More distant history is obscured by more changes • Among oldest lineages of ~3 billion years Bacteria and Archaea in particular, lots of “lateral gene ~2 billion years transfer.” Makes it difficult to infer relationships from phylogeny of single genes. A. Phylogeny How did we learn the existence of the Archaea? The Archaea and Bacteria are • Difference between both prokaryotic,but differ prokaryotes and more from each other than does the eukaryotes long been Archaea from the Eukarya known. (=plants, animals, fungi, protists). • Bacteria and Archaea are superficially similar • But they are genetically different: u The first Archaean genome was sequenced in 1996 - most genes were very different from bacterial genes - birth of the “three domain” concept I. Prokaryotes - Bacteria B. Morphology of prokaryotes and Archaea What are they • The prokaryotes are the most missing? numerous organisms on Earth Nuclei Membrane-enclosed organelles Cytoskeletons (actin and microtubules) What have they got •With tremendous diversity in that’s different from metabolism, habitats protists and animals? Cell wall 2 B. Morphology of the prokaryotes B. Morphology of the prokaryotes - Movement Prokaryotic cells are usually much Simple smaller than flagella eukaryotic cells Eukaryote Gas vesicles to Cell Closer to the size of a adjust buoyancy mitochondrion or Prokaryote cyanobacteria chloroplast Cell Is that a coincidence? Or gliding mechanisms spirochaete C. Ecology of the prokaryotes B. Morphology of the prokaryotes - Cell walls • How do prokaryotes reproduce? • Prokaryotic cell walls differ from • Asexually by fission those of eukaryotes. • Cell walls of Bacteria contain peptidoglycan (a polymer of amino sugars). Cell walls of Archaea contain proteins. Bacterial cell wall C. Physiology/metabolism of C. Physiology/metabolism of the prokaryotes prokaryotes • How do prokaryotes reproduce? • Prokaryotes - fairly narrow range • Asexually by fission of shapes and sizes, not very exciting movement: What have • Exchange genetic information prokaryotes been doing for more (e.g. by conjugation). In than 3 billion years? conjugation, • Learning chemical tricks DNA travels from donor to recipient via a cytoplasmic bridge 3 C. Physiology/metabolism of C. Physiology/metabolism of prokaryotes prokaryotes • All ancestral prokaryotes were • All living organisms need a source anaerobic, and some still are: of energy and a source of carbon in • Anaerobic: metabolism in the order to survive and grow absence of oxygen • What is the source of our energy • Aerobic: metabolism that requires and carbon? oxygen • We ingest molecules for both • Some can shift back and forth energy and carbon, so we’re heterotrophs • Most Bacteria and Archaea are heterotrophs as well C. Physiology/metabolism of C. Physiology/metabolism of prokaryotes Prokaryotes • What do plants do for energy and • Others have completely unique carbon? solutions, not found in eukaryotes • They use light for energy and C02 • Some use simple nitrogen or sulfur for carbon. Some prokaryotes do compounds for energy, but CO for as well - e.g. Cyanobacteria. These 2 carbon (needing neither light nor are autotrophs organic compounds for food!). • Why were Cyanobacteria so • Called chemolithotrophs important in the • Have enabled life in extremely history of life inhospitable places! on Earth? C. Physiology/metabolism of C. Physiology/metabolism of the prokaryotes the prokaryotes • Some chemolithotrophs Lastly, some live near deep sea use light for energy, hydrothermal vents at up to 2,500 m deep where but need food for there is no light. carbon: • Prokaryotes (mostly photoheterotrophs Archaea) that use hydrogen sulfide from deep sea volcanic vents for energy provide food for an entire bizarre community. 4 C. Physiology/metabolism of C. Physiology/metabolism of the prokaryotes the prokaryotes • Other chemical tricks • Paederus has long • Fix nitrogen from been known because atmosphere if crushed against • Digest cellulose skin causes rashes • Produce amazing • Produces pederin, a toxins polyketide like polyketides • Pederin also has (many antibiotics, anti-tumor activity e.g. tetracycline, • Guess where anti-tumor drugs) Paederus gets its • Polyketide in pederin? Paederus beetle Paederus beetle Paederus D. Ecology of the prokaryotes D. Ecology of the prokaryotes - extreme habitats • Some Archaea are • Some anaerobic Archaea produce heat-loving and acid- methane from CO2 as a key part of loving. their energy metabolism. • Some live in hot • They account for the methane in the sulfur springs and die atmosphere. of “cold” at 131°F (55°C) Archaea in sulfurous volcanic vent D. Ecology of the prokaryotes D. Ecology of the prokaryotes Some of these methane producers live in More about those prokaryotes in the guts of herbivorous animals mammalian guts - the human gut flora How many cells relative to other cells in our body? About how many species of bacteria? How much of your weight is bacteria? 5 D. Ecology of the prokaryotes D. Ecology of the Role of gut flora? prokaryotes Long thought to be commensal - i.e. • Some prokaryotes play key roles in beneficial to the bacteria, neutral for us global nitrogen cycles. E.g., nitrogen Recent research tells a very different fixers, nitrifiers, and denitrifiers. story Fig. 37.8 in Nitrogen fixation – E.g. bacteria are important for digesting your text carbohydrates, and variation in out of the air efficiencies between individuals may Nitrification – from explain variation in tendencies towards one solid form to obesity another better for Also influence immune system (and plants autoimmune diseases) in development Denitrification – back to the air The Bacteria E. Important prokaryotic groups - just a few The Proteobacteria • By far the biggest • There are far more known group of Bacteria Bacteria than Archaea. • Includes Rhizobium, the nitrogen fixing bacterium found in legume root nodules. • Also Salmonella, cholera, and E. coli. The Bacteria The Bacteria: The Proteobacteria Cyanobacteria Mitochondria evolved • Cyanobacteria are from Proteobacteria photosynthetic by endosymbiosis. •They created the oxygen atmosphere •Chloroplasts evolved from cyanobacteria by endosymbiosis •Makes you think differently about “pond scum,” no? 6 The Bacteria: Spirochaetes The Bacteria: Chlamydias Chlamydia are among • Spirochaetes are the tiniest living corkscrew shaped things. •Move by axial Almost all parasites, filaments e.g. a sexually transmitted disease of •Some are parasites humans of humans, e.g. Have complex life agent causing cycle with two stages: syphilis, Lyme a resting stage gets disease taken into host cell, the other grows and divides E. Important prokaryotic groups : II. The origin of the Summary of the Archaea eukaryotic cell • Archeans differ from Bacteria: • Step 1? (no one knows the Cell wall: proteins not sequence) Increase in size peptidoglycans • A central problem with being big is •Very different genetically that surface area doesn’t increase as fast as volume, yet surfaces are •Archeans often live in extreme needed for gas exchange and habitats: tolerate high feeding temperature, salt, low pH, • What’s the solution? absence of oxygen. II. The origin of the The origin of the eukaryotic cell eukaryotic cell Step 2? Infolded What’s the solution? plasma membrane attached to the chromosome may Lose the cell wall, allow infolding have led to a nuclear of the plasma envelope. membrane to Step 3? A primitive increase area cytoskeleton of actin and microtubules evolved. This allowed cell to change shape and move things around 7 II. The origin of the eukaryotic cell • The first eukaryotes were anaerobic. • But as oxygen increased, the oxidizing atmosphere was poisonous to anaerobes. • Step 4? Engulfing an aerobic proteobacterium resulted in mitochondria. • (Step 5? For some) Some organisms engulfed cyanobacteria and become photosynthetic (chloroplasts). 8.
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