THE ORIGIN OF LIFE HOW DID IT ALL BEGIN?

FORMATION OF THE EARTH 4.55 billion years ago Earth formed by accretion of matter. Constant bombardment heated the Earth and melted elements. Heavier elements sank to the center where nuclear decay released more heat. Gases were released by volcanic activity and incoming comets. NO LIFE WAS POSSIBLE

THE EARLY ATMOSPHERE A reducing atmosphere was present. Possible gasses: H 2 O, NH 3, CH 4, H 2, CO 2. Ammonia would have broken down: 2NH 3 N 2 + 3H 2 (escaped to space) Final content was probably H 2 O vapor, CO 2 and CO, N 2 (80%). NO OXYGEN

REQUIREMENTS FOR LIFE 1.Lack of oxygen (reducing atmosphere). 2.Appropriate chemicals (water, organic and inorganic molecules) 3.Sources of energy (U.V., heat, lightning) 4.Great amounts of time NO ENZYMES WERE PRESENT REACTIONS WERE SLOW

Investigating Pre-biotic Earth 1924, Oparin (Russian) and 1929, Haldane (American) Oparin’s Hypothesis – Conditions on the early Earth favored chemical reactions that synthesized organic molecules from inorganic components. Monomers Polymers Aggregates Coacervates exhibit emergent properties.

Sidney Fox’s Microspheres Fox mixed amino acids together with clay particles. Clay enhances polymerization process. Drying and heat formed polypeptides. Microspheres exhibit emergent properties: Accumulate monomers, catalyze rxn’s, bud, double-layer membrane, internal structure.

Haldane Oparin Fox

Urey & Miller’s Experiment 1953, Stanley Miller & Harold Urey, at the University of Chicago. Methane, ammonia, hydrogen, water. Energy sources were heat and continuous electric sparks. After 1 week, 15% of carbon was in the form of organic compounds. 2% of carbon formed amino acids. Showed abiotic synthesis was possible.

Miller & Urey’s Apparatus Miller

Juan Oro, 1961 Found that hydrogen cyanide and water could form amino acids in water. Produced large quantities of adenine

Murchison Meteorite Sept. 28, 1969, Murchison, Australia. 100 killograms recovered. Fragments showed 19 amino acids found in living things. Amino acids may have come to Earth from space (comets, asteroids, dust)

Possible Sites for the Origin of Life Extraterrestrial Seeding (Panspermia Theory). Deep sea hydrothermal vents Frozen Ocean Theory – Less luminous Sun 3 billion years ago. 300 meters of shielding ice over slightly saline oceans provided U.V. and meteorite protection. Organics accumulate. Combination of the above?

Many Processes Combined To Produce Life

What about genetic material Bases can be formed abiotically. Sugars and phosphates also form abiotically. Polymerization results in ribonucleotides. Further polymerization results in RNA. RNA has catalytic (enzyme) properties Ribozymes are common in cells. RNA can build DNA (Reverse Transcription)

Protocells A membrane must be present to concentrate chemicals. Membranes self-assemble from polymers like proteins phospholipids, and alcohols. Protocells must concentrate and hold higher concentrations of materials within them so reactions can take place efficiently. Metabolism results from molecular evolution and chemical selection. Protocells must be self-replicating – Budding?

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