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1 The Origin and Early History of Life Chapter 4 Slide 2 2 Where the first cell came from? Or.Can life arise from non-life? Can we test this scientifically? Conditions on early earth Formation of organic molecules Chemical evolution Primitive cell Prokaryotes Eukaryotes Multicellular organisms warm little pond Slide 3 3 What do we know? Slide 4 4 Are we alone? A.Yes B.No Slide 5 5 Which one represents possible origin of life on earth? A. Extraterrestrial aliens brought it B. Came with meteors from other planets C. Some superhuman powers created it D. Chemicals from primordial soup combined to make life E. None of the above Slide 6 6 We dont know how life originated. Probably arose on Earth, but an alternate theory suggests it arose elsewhere and drifted through space to seed the Earth Slide 7 7 What does life need? Slide 8 8 A way of harnessing energy to do useful work, a way of storing and reproducing genetic information, a way to keep the inside separated from the outside. Which of these arose first is a matter of debate. Inheritance first or metabolism first? Or both simultaneously? However, once a genetic system is in place, natural selection will quickly improve the new life form. Slide 9 9 Some Theories Darwin thought life originated in a warm little pond. However, since his time we know that life can exist in a much larger range of environments, and many theories now focus on high temperature and pressure environments such as a the bottom of the ocean or deep underground. The RNA World: a theory that puts genetics at the center. Iron-sulfur world: puts metabolism first Clay minerals: life started as self- reproducing clay crystals Slide 10 10 Origins of Life The Scientific Story Slide 11 11 Prebiotic Earth Conditions on the primitive Earth were not the same as those present today No spontaneous generation of life today (Pasteur) because the necessary conditions no longer exist. 2010 Paul Billiet ODWSODWS J.B.S. Haldane (credit: Bassano and Vandyk Studios) Image Credit A.I. OparinA.I. Oparin Slide 12 12 Origin of the Universe and the Earth Life most likely emerged under high-temperature conditions. 15 billion years ago The Big Bang led to the formation of the stars of the universe The sun is the closest star to us 4.6 billion years ago Planets of our solar system were formed including our earth Slide 13 13 Conditions on Early Earth- Reducing Atmosphere Early atmosphere is often referred to as a reducing atmosphere on the primitive Earth. No free oxygen (O 2 ) exact conditions unknown ample availability of hydrogen atoms very little oxygen Slide 14 14 Conditions of the early earth: The Earths surface temperature probably hotter than today very hot, barren rock, volcanoes Lightning, ultraviolet radiation gases: Free hydrogen : hydrogen (H 2 ) (Hydrogen sulfide/Hydrogen cyanide saturated hydrides methane (CH 4 ) ammonia (NH 3 ) water vapor (H 2 O) Energy for chemical reactions between these gases could come from electric discharge in storms or solar energy (no ozone layer) Slide 15 15 Then what? The earths temperature cooled over many years resulting in condensation and huge rains. Oceans formed and covered the earth. These oceans were thought to be near boiling point. Chemical Evolution took place, rearranging the atoms of the gases of the atmosphere in to the building blocks of organic compounds. Slide 16 16 Organic Compound Building Block Protein Amino Acids Nucleic Acids Nucleotides Carbohydrates Simple Sugars Lipids Glycerol and Fatty Acids Slide 17 17 1950s Miller-Urey Experiment Attempted to reproduce early reducing atmosphere and produce organic compounds from inorganic materials hydrogen-rich electrical discharges After a week 15 amino acids in the mixture Other biologically important molecules had been formed including ethanoic acid, lactic acid and urea Later similar experiments were done using CO 2 that produced nucleotides. Slide 18 18 Urey and Miller Produced amino acids carbohydrates lipids Nucleotides Conclusion? Perhaps the building blocks of organic compounds could have formed on primitive earth (Chemical Evolution) Image Credit Stanley MillerStanley Miller Slide 19 19 Conclusion These experiments cannot reproduce the exact conditions on the primitive Earth We shall never know exactly what happened BUT it can be shown that the basic building blocks for the large macromolecules can be synthesised in vitro from inorganic compounds. 2010 Paul Billiet ODWSODWS Slide 20 20 Chemical Evolution If life originally arose from non-life, how might this have happened? Consider the following scenario Synthesis and accumulation of small organic molecules Joining of these monomers into polymers Aggregation of these molecules into droplets to form localized microenvironments Origin of heredity Slide 21 21 The Jump It is thought that these compounds began to cluster together held by lipid molecules accumulating.. These clusters were called coacervates, or proteinoid microspheres Scientists believe that these abiotic proteinoid microspheres made the jump to become the first living cell approximately 3.5 billion years ago. Spontaneous Generation?? Slide 22 22 Sidney Fox (University of Miami) demonstrated the abiotic polymerization of organic monomers Polymers were formed when dilute solutions of organic molecules were dripped onto hot sand, clay, or rock Proteinoids - Clay can serve to concentrate these molecules Monomers bind to charged sites on clay particles - Metal ions in clay have catalytic function Polymer Formation Slide 23 23 From monomers to polymers Amino acids into polypeptides, could have occurred when dry or highly concentrated monomers are heated Condensation reactions take place forming peptide bonds between amino acids or phosphodiester bonds form between nucleotides. 2010 Paul Billiet ODWSODWS Slide 24 24 Early catalysts As molecules adsorb to the clay mineral particles they become concentrated (stick to the surface particles) These clay particles (coacervates) may have been essential catalysts in the formation of polymers. 2010 Paul Billiet ODWSODWS Slide 25 25 The first polynucleotides Once formed polynucleotides show a tendency to copy themselves using complementary base pairing This was probably catalysed by the presence of clay particles and metal ions These single stranded polynucleotides would have been the equivalent of RNA. 2010 Paul Billiet ODWSODWS Slide 26 26 A.DNA B.RNA C.Protein DNA RNA PROTEIN (Genetic information) (Information and catalytic) (Catalytic and structural) ? Which came first Most Likely Slide 27 27 RNA World One possible solution to needing both DNA to store genetic information and proteins to carry out activities is to use RNA for both. RNA can store information, and it can act as an enzyme. Perhaps there was a stage in the development of life with nothing but self- replicating RNA molecules. Proteins, DNA, and cell membranes added later in this scenario. No real evidence for it, but RNA works as an enzyme in some of the most basic life processes, such as making proteins. Slide 28 28 Abiotic RNA Replication Remember RNA enzymes? Slide 29 29 The first hereditary information RNA was probably the first hereditary molecule having the ability to copy itself RNA shows enzymic (catalytic) properties called ribozymes Polynucleotides are very good molecules at storing and transmitting information but they lack the versatility for all the chemical functions of a cell. 2010 Paul Billiet ODWSODWS Slide 30 30 A great partnership Polypeptides, which can form complex 3-dimensional structures (proteins), are much better at complex cell functions A partnership must have formed between the polynucleotides and the polypeptides The polynucleotides directed the synthesis of the polypeptides Today it is clear that information only flows from polynucleotides to polypeptides. Translation had started. 2010 Paul Billiet ODWSODWS Slide 31 31 The origin of DNA Later the hereditary information was probably stored in the form of DNA which is more stable than RNA The passage of information from RNA to DNA is possible in nature The reverse transcriptase enzyme of the retro viruses shows this. Image Credit: DNA DNA 2010 Paul Billiet ODWSODWS Slide 32 32 The first membranes, the first cells If a piece of RNA codes for a particularly good protein then there is nothing to stop that protein being used by other RNA molecules If however the RNA is enclosed in a membrane then it can keep its protein to itself and gains a selective advantage So membranes probably pushed evolution by natural selection forwards. 2010 Paul Billiet ODWSODWS Slide 33 33 Membranes defined the first cell The phospholipids form lipid bilayers when they are surrounded by water All the components of a simple prokaryotic cell were now assembled They diversified in their metabolism By 2 billion years ago free oxygen was appearing in the atmosphere due to the activity of photosynthetic bacteria. 2010 Paul Billiet ODWSODWS Slide 34 34 What did this first cell look like? The first cell was likely: Aquatic Prokaryotic Anaerobic Heterotrophic (Oparin and Haldanes Heterotroph Hypothesis) Slide 35 35 Biological Evolution now begins The following time line describes some of the big events: 2 billion years ago photosynthetic prokaryotes evolve releasing O 2 into the atmosphere. This brought about two major changes Aerobic environment Formation of ozone (O 3 ) UV-rays 2O 2 O + O + O + O O 3 + O Aerobic environment led to aerobic organisms evolving With 18X more energy they could grow faster, reproduce faster and evolve faster. Slide 36 36 What Happened Next? 1.5 billions years ago eukaryotes evolved Large prokaryotic cell engulfs a smaller prokaryotic cell. Resulted in the first eukaryotic cell (mitochondria and chloroplasts have their own DNA!!) Slide 37 37 Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. evolution.berkeley.edu/evolibrary/article/0_0_0/endosymbiosis_03 ENDOSYMBIOSIS BEGINNING OF THE EUKARYOTIC CELLS EVIDENCE FOR ENDOSYMBIOSIS DNA Slide 38 38 What likely followed? - Aquatic multicellularity NFB EvolutionNFB Evolution - Terrestrial Autotrophs - Terrestrial Heterotrophs How Did Life Begin? How Did Life Begin 2 How Did Life Begin?How Did Life Begin 2 Slide 39 39 Slide 40 40 Iron-Sulfur World A metabolism first scenario involves naturally occurring iron sulfide (also called pyrite) crystals. These crystals can catalyze both oxidation- reduction reactions (producing energy) and polymerizations of amino acids. Works especially well at high temperatures and pressures, such as are found in deep ocean vents called black smokers. Very small pores in the rocks make good chambers that take the place of membranes. An active self-sustaining metabolic system in the absence of inheritance. Some nucleic acids randomly polymerized by the Fe-S crystals eventually colonized the pores and had the property of self-replication. Slide 41 41 Origin of protobiots Bubble theories (Oparin) Slide 42 42 PROTO-CELLS Chemical evolution ultimately led to the formation of proto-cells Membrane-surrounded sacs containing genetic material and metabolically-active molecules Such structures have been experimentally produced From these proto-cells, cells ultimately arose Slide 43 43 Earliest Cells Microfossils have been found in rocks as old as 3.5 billion years old. resemble prokaryotes Stromatolites Slide 44 44 EARLIEST LIFE The earliest cells were prokaryotic Lack a membrane-bound nucleus Early in the history of life, populations diverged into two major lineages bacteria archaea & eukaryotes Slide 45 45 Archaebacteria Extreme-condition prokaryotes lack peptidoglycan in cell walls methanogens extreme halophiles extreme thermophiles thought to have split from Bacteria 2 bya. Slide 46 46 Bacteria Second major group of prokaryotes strong cell walls simpler gene structure contains most modern prokaryotes includes photosynthetic bacteria cyanobacteria Slide 47 47 EARLIEST LIFE How do we know that domain Eukarya is more closely related to domain Archaea than to domain Bacteria? Analysis of rRNAs and other highly conserved genes and proteins provide the strongest evidence Slide 48 48 First Eukaryotic Cells Eukaryotes probably arose about 1.5 bya. Internal membrane-bound structures such as mitochondria and chloroplasts are thought to have evolved via endosymbiosis. Energy-producing bacteria were engulfed by larger bacteria. beneficial symbiotic relationship Slide 49 49 First Eukaryotic Cells Sexual reproduction Eukaryotic cells can reproduce sexually, thus allowing for genetic recombination. Genetic variation is the raw material necessary for evolution. Multicellularity arisen many times among eukaryotes fosters specialization Slide 50 50 What they have and what they dont Slide 51 51 What about this group? Slide 52 52 That is the end Slide 53 53 Summary Fundamental Properties of Life Origin of Life Hypotheses Chemical Evolution Cell Origin Theories Bubble Theories Prokaryotic Cells Archaebacteria Bacteria Eukaryotic Cells Extraterrestrial Life Slide 54 54 Slide 55 55 Development of new branches on the TREE Slide 56 56 TAXONOMY Slide 57 57 Extraterrestrial Life Universe has 10 20 stars similar to our sun. Conditions may be such that life has evolved on other worlds in addition to our own. ancient bacteria on Mars. largest moon of Jupiter, Europa, covered with ice. liquid water may be underneath Slide 58 58 The Domains and Kingdoms Slide 59 59 What have we learned so far? Cell theory All living organisms are made of cells, and all living cells come from other living cells. Molecular basis of inheritance DNA encodes genes which make-up and control living organisms. Evolutionary change Life-forms have evolved varying characteristics to adapt to varied environments. Evolutionary conservation Some characteristics of earlier organisms are preserved and passed on to future generations. Slide 60 60 Lets make something with those molecules Aggregations of abiotically produced molecules Preceded living cells Laboratory experiments have demonstrated their formation from organic compounds Protobionts and liposomes