P10-Lecture 17- Origins of Life.ppt - March 22

P10-Lecture 17- Origins of Life.ppt - March 22 - The Origin...

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Unformatted text preview: The Origin of Life s s Recall: Tree Related concepts Origins - How did life arise? The Shape of the Tree x Diversity, abundance, and features of major groups s Factors influencing the Shape of the tree, e.g. x "Key Innovations" and their consequences (wings; flowers) x Major transformations x Major Radiations x Borrowing and merging - the tangled tree x Convergence What is life? Or, phrased another way ... What is the transition from chemistry to biology? Origins - How? Today Origin of Life - Three problems "The mother of all questions" x Instead, test plausibility of steps s 1) We can't observe, even indirectly, the earliest steps s 2) Even simplest forms of life very complex x How does this complexity form? s 3) Which, if either, came first? x DNA - Great for information storage, little else x Proteins - Do work, require information from DNA to be assembled At least four BIG steps to life (steps 3 & 4 order is not impt.) s 1) Formation of small organic compounds s 2) Formation of complex polymers s 3) Formation of liposomes to protect complex polymers (and more) s 4) Formation of a system of selfreplication At least four BIG steps to life s 1) Formation of small organic compounds x E.g. Amino acids, nucleotides, sugars, etc. x How? x Oparin and Haldane theory 3 Early 3 Early (in text) atmosphere had little oxygen atmosphere was reducing (lots of CH4, NH3, H2) 3 This favored reactions forming organic molecules At least four BIG steps to life s 1) Formation of small organic compounds x Miller and Urey - test x Created a reducing atmosphere, spark Fig. 3.1 At least four BIG steps to life s 1) Formation of small organic compounds x From elsewhere? x Asteroids have lots of organic material 3 E.g. amino acids x The early Earth was bombarded with meteors x Panspermia Hypothesis - Organic material (or Life itself!) from elsewhere At least four BIG steps to life s 2) Formation of polymers (p. 50) x Possible without cellular catalysts? x Need to concentrate monomers 3 E.g. Yes. by drying inorganics can do this - e.g. clays x Need to catalyze reaction inorganically 3 Many x Not a huge obstacle 3 Not hard to do experimentally At least four BIG steps to life s 3) Formation of liposomes x "aggregates (total/combined) of abiotically produced molecules" x Can spontaneously form Fig. 6.7a At least four BIG steps to life s 3) Liposomes: x Can carry out cell-like processes xStore energy across membrane xTake-up and release "metabolites" At least four BIG steps to life s 4) Formation of a system of self-replication x Information, and a means of replicating it x May have preceded association with liposomes x Problem: 3 Which came first - DNA or the proteins used to make it? Proteins 3 Perhaps there's an alternative DNA The "RNA world" s In 1989 Altman, Cech receive a Nobel Prize x 1982: found an enzyme that cut and spliced nucleic acids--but poorly! Okay, what's the big deal? s The enzyme was an RNA - not a protein!! x And so ...? The "RNA world" s RNA carries genetic information (like DNA) s RNA can catalyze reactions (including formation of RNA) s Phenotype and Genotype!! Selection can favor variants with effective replication! Back to Complexity and "Design" s Natural Selection xVariation xHeritable variation xStruggle xDifferential reproduction based on heritable variation xChanges in characteristics of the population - evolution RNA World - Three problems s 1) In the absence of cells, products of ribozyme activity would be shared x Liposomes help s 2) Self-replication of large RNAs - "The Holy Grail of Origins of Life Research" - has not been demonstrated x But seems increasingly plausible s 3) Initial formation of RNA - Tough to imagine x Pre-biotic clutter - especially left-handed nucleotides x Perhaps a "Pre-RNA" world? Pre-RNA World? s Proteins? x Can form abiotically x Can polymerize abiotically x Can catalyze their own replication Joyce, G. 2002. Nature 418:212-221 Origins of Life - Summary s Life is ..... s Four big steps to life x Organics, polymers, boundaries, information x DNA/protein world preceded by an RNA world 3 Ribozymes - Genotype, phenotype, selection x RNA world preceded by ? Prokaryotes--Diversity s They are everywhere! ubiquitous s Extreme metabolic diversity s Crucial for many global processes x We need them more than they need us! s Unlike eukaryotes, prokaryotes have: x No nuclear envelope x No membrane-bound organelles x Circular DNA, with relatively few genes "Prokaryotes" - Classification s Formerly all prokaryotes lumped together. This is wrong! Fig. 28.11 "Prokaryotes" - Classification s Formerly all prokaryotes lumped together: x Kingdom Monera is out. s Three Domains of life s Prokaryotes: x Bacteria x Archaea See www.tolweb.org for phylogeny 28.1 Prokaryotes - Two Domains Bacteria Archaea Eukarya Organelles, nucleus Linear chromosomes Mitosis and meiosis LUCA(C) RNA world? Abiogenesis DNA/Proteins RNA, ribosomes Circular Chromosome "Prokaryotic" Metabolic Diversity Why is this interesting and important? s 1) Appreciate diversity of prokaryotes s 2) Implications for early Earth environment and the early evolution of life s 3) A very specific point about evolution s 4) Implications for the origin of Eukaryotes s Unlike most Eukaryotes, Swapping Genes (Box 28.2) Lateral (= Horizontal) Gene Transfer "prokaryotes" can laterally transfer genes! x Very important for evolution s Various mechanisms x E.g. transformation, transduction, conjugation. Know general Energy and Carbon s Two Basic Requirements: x ENERGY x CARBON for synthesis of organic compounds s Needn't come from the same source s 1. Energy x Phototrophs use light x Chemotrophs use chemical compounds s 2. Carbon x Autotrophs use CO2 x Heterotrophs use organic compounds Some Basic Metabolism: Energy Transformations to make ATP s Glycolysis / Fermentation x Glucose (high potential energy) broken down x Energy used to produce ATP x Very widespread! Ancient! x Not particularly efficient x Anaerobic s Aerobic Respiration s Photosynthesis 9.17 Some Basic Metabolism: Energy Transformations to make ATP s Glycolysis s Aerobic Respiration x Continues breakdown started in glycolysis x Much higher yield of ATP! x Electrons passed down electron transport chain to an electron acceptor 3 Usually O2 3 Energy harnessed to produce ATP s Photosynthesis Some Basic Metabolism: Energy Transformations to make ATP s Glycolysis s Aerobic Respiration x Fig. 28.15 x See also 9.22 s Photosynthesis Some Basic Metabolism: Energy Transformations to make ATP s Glycolysis s Aerobic Respiration s Photosynthesis x Light energy transmitted to electron x Electron passed down electron transport chain 3 Energy harnessed to produce ATP 3 Electrons come from splitting water, resulting in release of O2 (usually) Some Basic Metabolism: Energy Transformations to make ATP s Glycolysis s Aerobic Respiration s Photosynthesis x Fig. 10.16 x Also, add P. 210 column one to reading Energy and Carbon - Combinations s Autotrophs x Photoautotrophs 3 Energy from light, carbon from CO2 3 E.g. plants, some prokaryotes e.g. cyanobacteria x Chemoautotrophs 3 Energy from organics, carbon from CO2. 3 Some prokaryotes, e.g. archaea (chemolithotrophs- oxidize inorganics like methane) Energy and Carbon s Autotrophs s Heterotrophs x Photoheterotrophs 3 Energy from light; Carbon from organic sources 3 E.g. Some prokaryotes x Chemoheterotrophs 3 Energy and Carbon from organic sources. 3 E.g. some prokaryotes, us. Photosynthesis Energy from the sun! s Use light as an energy source for making ATP (Light reaction) x O2 2 as a by-product 2 s Use ATP to create sugars from CO2 s These are now photoautotrophs s The oxygen revolution: x Good news, bad news The oxygen revolution: Good news, bad news s Origin of cynaobacteria x Increased Oxygen levels x Oxygen is very reactive - breaks bonds x Bad news for anaerobic organisms s But, allowed the evolution of aerobic respiration! Aerobic Respiration s Much greater yield of ATP s In some ways, the opposite of Photosynthesis x Photosynthesis: 3ATP (from Light rxn) + CO2 Sugar + O2 + O2 ATP + CO2 x Aerobic respiration: 3Sugar Evolution is a tinkerer s 1) Pathways for production of ATP in aerobic respiration apparently borrowed from photosynthesis s 2) Anaerobic origins of photosynthesis apparent even in modern plants x Enzymes used for fixing CO 2 are interfered with by O2 -- photorespiration Diversity of Prokaryotes - Bacteria s Very diverse and widespread s Occupy a wide range of habitats s Important to humans xCause many diseases xNutrient cycling 3E.g. Nitrogen xResearch Cyanobacteria Photoautotrophs Diversity of Prokaryotes - Bacteria Diversity of Prokaryotes - Archaea Diversity of Prokaryotes - Archaea s They can inhabit extreme environments: xMethanogens - Important decomposers 3Use H2 to reduce CO2 to methane in water 10x as salty as the ocean xHalophiles 3Thrive xThermophiles - up to 105 C xAcidophiles - in pH below 1.0! 31.0 is Battery acid s Prokaryotes 3 Archaea 3 Photo, Summary x Paraphyletic - Archaea closer to us! is monophyletic x Extremely diverse metabolism Chemo autotrophs; Photo, chemo heterotrophs x Arose in an anaerobic worldx Rise of photosynthesis allowed aerobic respiration 3 Evolution borrowed pathways from photosynthesis x Diversity of Bacteria 3 Examples x Diversity of Archaea 3 Examples ...
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This note was uploaded on 05/11/2010 for the course BIOLOGY 105 taught by Professor Richard during the Spring '10 term at George Mason.

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