Bio 100 Study Guide 14 http://www.swarthmore.edu/natsci/cpurrin1/evolk12/slm/origindayimages/06soup.jpg
The Origin of Life 1. Conditions on early earth 2. Abiogenic synthesis organic molecules 3. Hot rocks and clay help to form polymers 4. RNA world and aggregates 5. Why prokaryotes are critical to life on earth
The analogy of a clock can be used to place major events in the Earth s history in the context of the geological record Cenozoic Humans Land plants Animals Origin of solar system and Earth 1 4 Multicellular eukaryotes Proterozoic Eon Archaean Eon Billions of years ago 2 3 Single-celled eukaryotes Atmospheric oxygen Prokaryotes
Working Backwards the Age of the Earth Radioactive decay is consistent with an age of 4.5 Billion Years http://www.cbu.edu/~jholmes/n111/part24/sld018.htm
Conditions on early Earth made the origin of life possible Most biologists now think that it is at least a credible hypothesis That chemical and physical processes on early Earth produced very simple cells through a sequence of stages According to one hypothetical scenario There were four main stages in this process
Four Stages of Prebiotic Chemical Evolution Abiotic synthesis of small organic molecules Joining of monomers into polymers Origin of heredity RNA world Aggregation of o.m. into protobiont droplets
STRATIGRAPHY http://www.gobiernodecanarias.org/educacion/penelope/strat3.gif http://earthsci.org/fossils/palaeo/images/scale.gif
The earliest stromatolite of confirmed microbial origin dates to 2,724 million years ago. Modern stromatolites in Shark Bay, Western Australia. http://www.resa.net/nasa/images/mars/stromatolite.jpg
There are a variety of potential sources of the organic monomers that started life! a. Outer space b. The atmosphere c. Meteorites d. Oceans deep sea hydrothermal vents
Synthesis of Organic Compounds on Early Earth Earth formed about 4.6 billion years ago Along with the rest of the solar system Earth s early atmosphere Contained water vapor and many chemicals released by volcanic eruptions
Laboratory experiments simulating an early Earth atmosphere Show that organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere. Have produced organic molecules from inorganic precursors, but the existence of such an atmosphere on early Earth is unlikely
Apparatus for the Miller-Urey Experiment http://www.physics.hku.hk/~tboyce/sfseti/15origin.html http://upload.wikimedia.org/wikipedia/commons/4/40/ureymillerexperiment.jpeg
Instead of forming in the atmosphere The first organic compounds on Earth may have been synthesized near submerged volcanoes and deep-sea vents Figure 26.3
Extraterrestrial Sources of Organic Compounds Some of the organic compounds from which the first life on Earth arose May have come from space Carbon compounds Have been found in some of the meteorites that have landed on Earth
Looking Outside Earth for Clues About the Origin of Life The possibility that life is not restricted to Earth Is becoming more accessible to scientific testing
Abiotic Synthesis of Polymers Small organic molecules Polymerize when they are concentrated on hot sand, clay, or rock
Pyrite - FeS ORIGIN OF LIFE: Life as We Don't Know It Wächtershäuser Science 25 August 2000: 1307 Pyrite and the origin of life K. R. POPPER Nature 344, 387 (29 March 1990); doi:10.1038/344387a0
PYRITE World http://www.wellesley.edu/chemistry/chem227/origins/1307-1-med.gif
One reason why it is suggested that the initial formation of biological-like polymers must have taken place on the surfaces of minerals was: Minerals provide a dry surface for the dehydration reactions needed to produce biological polymers.
Optical Activity is an Issue http://www.btools.com/images/fig1.gif
Protobionts Are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Laboratory experiments demonstrate that protobionts Could have formed spontaneously from abiotically produced organic compounds For example, small membrane-bounded droplets called liposomes Can form when lipids or other organic molecules are added to water
20 m Glucose-phosphate Glucose-phosphate Phosphorylase Phosphate Starch Maltose Amylase Figure 26.4a, b (a) Simple reproduction. This liposome is giving birth to smaller liposomes (LM). Maltose (b) Simple metabolism. If enzymes in this case, phosphorylase and amylase are included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products.
Natural section could refine protobionts containing hereditary information Once primitive RNA genes and their polypeptide products were packaged within a membrane, the protobionts could have evolved as units. Molecular cooperation could be refined because favorable components were concentrated together, rather than spread throughout the surroundings. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.13
Early protobionts with self-replicating, catalytic RNA Would have been more effective at using resources and would have increased in number through natural selection
"Metabolism" of a Coacervate The properties of artificial coacervates are similar to some of the properties of living cells. They are held intact by a non-lipid membranelike coating. Chemical reactions take place in the interior in the presence of enzymes. http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/25.03.jpg
http://exobiology.nasa.gov/ssx/biomod/origin_of_life_slideshow/prebiotic_bio_path.big.jpg
Progression to a Protocell http://exobiology.nasa.gov/ssx/biomod/origin_of_life_slideshow/molecules.protocell.big.jpg
Misconception: Evolution is a theory about the origin of life. http://evolution.berkeley.edu/evosite/misconceps/iaorigintheory.shtml
The RNA World and the Dawn of Natural Selection The first genetic material Was probably RNA, not DNA
RNA molecules called ribozymes have been found to catalyze many different reactions, including Self-splicing Making complementary copies of short stretches of their own sequence or other short pieces of RNA 3 Ribozyme (RNA molecule) Template Nucleotides Figure 26.5 Complementary RNA copy 5 5
The first ribozymes found in bacteria were self-splicing introns. http://138.192.68.68/bio/courses/biochem2/rna/selfsplicingrna.html
A Ribozyme from a Protist The folded three-dimensional structure of this catalytic RNA, or ribozyme, enables it to catalyze chemical reactions during protein synthesis. RNA catalysis may have preceded enzyme catalysis in the evolution of life. http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/25.04.jpg
http://exobiology.nasa.gov/ssx/biomod/origin_of_life_slideshow/rnaworldcritique.big.jpg
The End