CLASS 10 - origin of life (no movies).pptx.pdf

Primate Evolution  Rough Estimates Humans split from other primates 2 MYA Birds, Reptiles, Mammals become distinct – 200-500 MYA Multicellularity 1000 MYA Eukaryotes 2000 MYA First Prokaryotes 3500 MYA  Bacterial fossils (3.5 BYA!) Cyanobacteria – pigment le...

Primate Evolution  Rough Estimates Humans split from other primates 2 MYA Birds, Reptiles, Mammals become distinct – 200-500 MYA Multicellularity 1000 MYA Eukaryotes 2000 MYA First Prokaryotes 3500 MYA  Bacterial fossils (3.5 BYA!) Cyanobacteria – pigment leaves behind chemical signatures http://www.ucmp.berkeley.edu/bacteria/bacteriafr.html  Origins of Life Today all cells come from pre-existing cells The Earth formed as a hot mass of molten rock about 4.5 billion years ago (BYA) As it cooled, chemically-rich oceans were formed from water condensation We have evidence of really old cells? How and Why did they form? Many competing hypotheses, but no Theories  Beginnings… Some basic questions that need to be answered when discussing the origin of life. (1) Where did the raw materials for life come from? (2) How did an isolated cell form? (3) What did the early genome resemble? Hard to answer these questions. We have to study something that happened 4 billion years ago! NO THEORIES, ONLY HYPOTHESES! Where did all the building blocks necessary for life to evolve come from?  Earth 4.6-3.8 billion years ago (Hadean Earth). Journal of Cosmology, Volume 8, June 2010 Early Earth (4.5 BYA) had no atmosphere. Gases near the surface heated so quickly that they were immediately lost to space The planet Theia collided with the young earth and created our moon and part of a new atmosphere http://scijinks.jpl.nasa.gov/atmosphere-formation/ http://www.joetucciarone.com/joespace.html Continual bombardment by meteors produce violent volcanic eruptions. The volcanoes spewed water, C02, and NH3 into the atmosphere. Much of CO2 was dissolved into the newly forming oceans Synthesis of Organic Compounds on Early Earth Earth formed about 4.6 billion years ago, along with the rest of the solar system First organisms emerged between 3.8 and 2.5 BYA Early atmosphere composition not agreed on Initially hypothesized that it may have been a highly reducing atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)  A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment Would have made it easier to form carbon-rich molecules Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible Reduction is chemical reaction that involves the gaining of electrons by one of the atoms involved in the reaction. Here, Fluorine (F₂) gets reduced to hydrogen fluoride.  Results Found within a week that methane gas (CH₄) converted into other simple carbon compounds Compounds combined to form simple molecules and then more complex molecules Later experiments produced more than 30 carbon compounds including amino acids Adenine also produced Main problem: More recent studies argues that the earth’s gaseous atmosphere was not made of reducing gases. Miller-Urey’s experiment may be applicable to other environments Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents Iron-sulfur clusters, which are found in deep sea vents, may have catalyzed the first chemical reactions How did an isolated cell form?  Protocells Protocells are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Protocells exhibit simple reproduction and metabolism and maintain an internal chemical environment Replication and metabolism are key properties of life Miller-Urey experiment may explain the origin of compounds but now how they are properly assembled Need a membrane to surround organic material Need a simple mechanism of “division” and “growth”  Phospholipids are special molecules that can self arrange into encapsulating membranes! ? Lipids may have concentrated in those deep sea vents to form micelles Small channels mimic the narrow tubes of thermal vents The heating of the channel leads to convection Budin et al., 2009 An attempt to recreate the conditions of a hydrothermal vent The dye moves around the capillary like little race cars Budin et al., 2009 When a low concentration of lipids were added… You can see the formation of vesicles with encapsulated dye!!! If it can encapsulate dye, it could encapsulate amino acids, small molecules, even RNA!  How do vesicles replicate? Lipids form micelles Micelles fuse together to make a long tube The tube is agitated and breaks into man small vesicles Schrum et al. 2010  Panspermia – life exists throughout the universe Earth may have been “seeded” with life or materials for life from some other planet Meteor or cosmic dust may have carried complex organic molecules to earth Kicked off evolution of life Amino acids have been found on meteorites Different proposed hypotheses Direct experimental evidence is hard to obtain you have to catch a meteor or send satellites deep into space How did genomes come to be? Good question!!! (we don’t really know)  Self-Replicating RNA and the Dawn of Natural Selection The first genetic material was probably RNA, not DNA DNA is a fairly unreactive molecule. Without the the support of RNA and proteins, DNA is useless In contrast, RNA is very reactive and flexible due to its structure RNA molecules called ribozymes have been found to catalyze many different reactions For example, ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA The most famous Ribozyme is the Ribosome Image from Wikipedia.org  RNA could have originally directed protein synthesis prior to DNA  Early protocells may have had self-replicating, catalytic RNA RNA molecules that support and strengthen the protocell would have been selected for New Adaptations would have allowed RNA to coordinate protein synthesis thereby further raising fitness of the protocell The early genetic material might have formed an “RNA world” Ribozyme that can Catalyze the production of RNA PDB: 3HHN  Why DNA? RNA is less stable because it has an accessible -OH group. Via chemical reaction, this group can result in the destruction of RNA. DNA does not have this free OH group (“deoxy”) RNA DNA http://www.atdbio.com/content/22/RNA-oligonucleotide-synthesis http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04/DNA_bbone.jpg Time line BYA Sophie Petit-Zeman, Nature 2002